本帖最后由 龟山淬火 于 2013-5-5 15:15 编辑
A DIY Induction Heater.感应加热遵循高频磁场感应原理.电路非常简单，只需几个常用元器件. 如图的感应器及其电路只需15V,5A就可在30秒内把起子口烧红。
控制电路用的是零压切换的方法使3极管高效地完成能量变换而3极管几乎不发热，另外一个重要特点是系统频率自适应于电感和电容。
How Does Induction Heating Work?When a magnetic field changes near a metal or other conductive object, a flow of current (known as an eddy current) will be induced in the material and will generate heat. The heat generated is proportional to the current squared multiplied by the resistance of the material. The effects of induction are used in transformers for converting voltages in all sorts of appliances. Most transformers have a metallic core and will therefore have eddy currents induced into them when in use. Transformer designers use different techniques to prevent this as the heating is just wasted energy. In this project we will directly make use of this heating effect and try to maximise the heating effect produced by the eddy currents.
If we apply a continuously changing current to a coil of wire, we will have a continuously changing magnetic field within it. At higher frequencies the induction effect is quite strong and will tend to concentrate on the surface of the material being heated due to the skin effect. Typical induction heaters use frequencies from 10kHz to 1MHz.
DANGER: Very high temperatures can be generated with this device!
The CircuitThe circuit used is a type of collector resonance Royer oscillator which has the advantages of simplicity and self resonant operation. A very similar circuit is used in common inverter circuits used for powering fluorescent lighting such as LCD backlights. They drive a center tapped transformer which steps up the voltage to around 800V for powering the lights. In this DIY induction heater circuit the transformer consists of the work coil and the object to be heated.
The main disadvantage of this circuit is that a center tapped coil is needed which can be a little more tricky to wind than a common solenoid. The center tapped coil is needed so that we can create an AC field from a single DC supply and just two N-type transistors. The center of the coil is connected to the positive supply and then each end of the coil is alternately connected to ground by the transistors so that the current will flow back and forth in both directions.
The amount of current drawn from the supply will vary with the temperature and size of the object being heated.
From this schematic of the induction heater you can see how simple it really is. Just a few basic components are all that is needed for creating a working induction heater device.
R1 and R2 are standard 240 ohm, 0.6W resistors. The value of these resistors will determine how quickly the MOSFETs can turn on, and should be a reasonably low value. They should not be too small though, as the resistor will be pulled to ground via the diode when the opposite transistor switches on.
The diodes D1 and D2 are used to discharge the MOSFET gates. They should be diodes with a low forward voltage drop so that the gate will be well discharged and the MOSFET fully off when the other is on. Schottky diodes such as the 1N5819 are recommended as they have low voltage drop and high speed. The voltage rating of the diodes must be sufficient to withstand the the voltage rise in the resonant circuit. In this project the voltage rose to as much as 70V.
The transistors T1 and T2 are 100V 35A MOSFETs (STP30NF10). They were mounted on heatsinks for this project, but they barely got warm when running at the power levels shown here. These MOSFETs were chosen due to having a low drain-sorce resistance and fast response times.
The inductor L2 is used as a choke for keeping the high frequency oscillations out of the power supply, and to limit current to acceptable levels. The circuit might work without it, but it is less efficient, and could lead to damage of the power supply or control circuit. The value of inductance should be quite large, but also must be made with thick enough wire for carrying all the supply current. If there is no choke used, or it has too little inductance, the circuit might fail to oscillate. The exact inductance value needed will vary with the PSU used and your coil setup. You may need to experiment before you get a good result. The one shown here was made by winding about 8 turns of 2mm thick magnet wire on a toroidal ferrite core. As an alternative you can simply wind wire onto a large bolt but you will need many more turns of wire to get the same inductance as from a toroidal ferrite core. You can see an example of this in the photo on the left. In the bottom left corner you can see a bolt wrapped with many turns of equipment wire. This setup on the breadboard was used at low power for testing. For more power it was necessary to use thicker wiring and to solder everything together.
As there were so few components involved, we soldered all the connections directly and did not use a PCB. This was also useful for making the connections for the high current parts as thick wire could be directly soldered to the transistor terminals. In hindsight it might have been better to connect the induction coil by screwing it directly to the heatsinks on the MOSFETs. This is because the metal body of the transistors is also the collector terminal, and the heatsinks could help keep the coil cooler.
The capacitor C1 and inductor L1 form the resonant tank circuit of the induction heater. These must be able to withstand large currents and temperatures. We used some 330nF polypropylene capacitors. More detail on these components is shown below.
The Induction Coil and CapacitorThe coil must be made of thick wire or pipe as there will be large currents flowing in it. Copper pipe works well as the high frequency currents will mostly flow on the outer parts anyway. You can also pump cold water through the pipe to keep it cool.
A capacitor must be connected parallel to the work coil to create a resonant tank circuit. The combination of inductance and capacitance will have a specific resonant frequency at which the control circuit will automatically operate. The coil-capacitor combination used here resonated at around 200kHz.
It is important to use good quality capacitors that can withstand large currents and the heat dissipated within them otherwise they would soon fail and destroy your drive circuit. They must also be placed reasonably close to the work coil and using thick wire or pipe. Most of the current will be flowing between the coil and capacitor so this wire must be thickest. The wires linking to the circuit and power supply can be slightly thinner if desired.
This coil here was made from 2mm diameter brass pipe. It was simple to wind and easy to solder to, but it would soon start to deform due to excess heating. The turns would then touch, shorting out and making it less effective. Since the control circuit stayed relatively cool during use, it seemed that this could be made to work at higher power levels but it would be necessary to use thicker pipe or to water cool it. Next the setup was improved to tolerate a higher power level...
AVAILABLE PARTS: Resistors, Diodes, Capacitors, MOSFETs, Heatsinks, Ceramic support, 4mm Brass Pipe, 4mm Copper Pipe, Clear PVC Tubing, Large Bolt, 30A Cable, 12V Water Pump, 12V Regulator
Pushing it FurtherThe main limitation of the setup above was that the work coil would get very hot after a short time due to the large currents. In order to have larger currents for a longer time, we made another coil using thicker brass tubing so that water could be pumped through when it was running. The thicker pipe was harder to bend, especially at the center tapping point. It was necessary to fill the pipe with fine sand before bending it as this prevents it from pinching at the sharp bends. It was then cleared out using compressed air.
The induction coil was made in two halves as shown here. They were then soldered together and a small piece of pvc pipe was used to connect the central pipes so that water could flow through the whole coil.
Less turns were used in this coil so that it would have a lower impedance and therefore sustain higher currents. The capacitance was also increased so that the resonant frequency would be lower. A total of six 330nF capacitors were used to give a total capacitance of 1.98uF.
The cables connecting to the coil were just soldered onto the pipe near the ends, just leaving room for fitting some PVC pipe.
It is possible to cool this coil simply by feeding water through directly from the tap but it is better to use a pump and radiator to remove the heat. For this, an old fish tank pump was placed in a box of water and a pipe fitted the outlet nozzle. This pipe fed to a modified computer CPU cooler which used three heat-pipes to move the heat.
The cooler was converted into a radiator by cutting the ends off the heat pipes and then linking them with PCV pipes to the the water would flow through all 3 heatpipes before exiting and going back to the pump.
If you do cut some heatpipes yourself, make sure to do it in a well ventilated area, and not indoors as they contain volatile solvents that can be toxic to breathe. You should also wear protective gloves to prevent skin contact.
This modified CPU cooler was very effective as a radiator and allowed the water to remain quite cool.
Other modifications needed were to replace the the diodes D1 and D2 with ones rated for higher voltages. We used the common 1N4007 diodes. This was because with the increased current there was a larger voltage rise in the resonant circuit. You can see in the image here that the peak voltage was 90V (yellow scope trace) which is also very close to the 100V rating of the transistors.
The PSU used was set to 30V so it was also neccesary to feed the voltage to the transistor gates via a 12V voltage regulator. When no metal was inside the work coil, it would draw about 7A from the supply. When the bolt in the photo was added, this went up to 10A and then gradually dropped again as it heated up beyond curie temperature. It would certainly go over 10A with larger objects, but the PSU used has a 10A limit.
The bolt you can see glowing red hot in the photo took about 30 seconds to reach maximum temperature. The screwdriver in the first image could now be heated red hot in about 5 seconds.
In order to go to higher power than this, it would be necessary to use different capacitors or a larger array of them so that the current was more distributed between them. This is because the large currents flowing and high frequencies used would heat the capacitors significantly. After about 5 minutes of use at this power level the DIY induction heater needed to be switched off so that they could cool down. It would also be necessary to use a different pair of transistors so that they could withstand the larger voltage rises.
In all this project was quite satisfying as it produced a good result from just a simple and inexpensive circuit. As it is, it could be useful for hardening steel, or for soldering small parts. If you decide to make your own induction heater project, please post your photos below. Please read through the other comments before making your own as it could save you time later on.
If you wish to simulate this project for testing different inductance values or transistor choices, please download LTSpice and run this DIY Induction Heater Simulation (Right click, Save as)
TroubleshootingIf you have trouble getting this working, here are a few tips to help troubleshoot your home made induction heater project....
PSU (Power Supply)
If your PSU is unable to deliver a large surge of current when the induction heater is powered on, then it will fail to oscillate. The voltage from the supply will drop during that moment (although the PSU may not display this) and this will prevent the transistors from switching correctly. To help with this problem, you can place several large electrolytic capacitors in parallel with the supply. When charged they will be able to deliver a large surge current to your circuit.
Choke (inductor L2)
This limits the power to your induction heater. If yours is not oscillating, then you may need more inductance to prevent voltage drop in your PSU. You will need to experiment with how much inductance you need. Better to have too much, than too little as this will only limit the power of the heater. Too little may mean it wont work at all.
Wiring
Keep the connecting wires short to reduce stray inductance and interference. Long wires add unwanted resistance and inductance to the circuit and can result in unwanted oscillations or poor performance.
Components
The transistors chosen must have a low voltage drop otherwise they will overheat, or even prevent the system from oscillating. The capacitors must have a low ESR (resistance) and ESL (inductance) so they can tolerate the high current and temperatures. The diodes should also have a low forward voltage drop so that the transistors switch off correctly. They should also be fast enough to work at the resonant frequency of your induction heater.
Powering it up
When switching it on, do not have metal within the heating coil. This can lead to larger current surges which could prevent the oscillation from starting as mentioned above. Also do not try to heat large amounts of metal. This project is only suitable for small induction heaters.
Brain
You will need a brain that functions reasonably well to make this project safely. If you are one of those people who is known by your friends as "a bit thick", then congratulations on being able to use a computer and navigate to this page, but unfortunately this project is not for you. It can be very dangerous to build an induction heater, so if you are new to electronics, you should get someone to help you make it. Approach things logically; If it is not working, check the components used are not faulty, check connections are correct, read this whole article and all the comments, search Google if you do not understand any of the terms, or read through our Learn Electronics section. Remember: Hot things will burn you and can set things on fire; Electricity can electrocute you and also cause fire. Put safety first.
Comments and questions for DIY Induction Heater The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
Tommy - Wednesday, 26th October 2011 1:07pm - #4640
What is the red waveform on the scope?
RMCybernetics - Wednesday, 26th October 2011 6:04pm - #4641
The red waveform is the gate voltage of the other transistor.
Marcus - Thursday, 27th October 2011 11:07pm - #4642
Could I use a pancake coil to make a stove style heater?
RMCybernetics - Friday, 28th October 2011 12:25pm - #4644
Yes you can.
Rusdi - Sunday, 30th October 2011 1:01am - #4646
I intend to buy 3sets of all the parts from u guys to build this, but I am a newbie in electronics, is there any special considerations to build this other than then current and voltage hazard? And whats with the osciloscope? anything special with the osciloscope, like it has to be grounded in some particular way or anything else? Or any other particular considerations?
Surastyo - Sunday, 30th October 2011 3:46am - #4648
I build this today and ended with burnt FET. I use FQP60N06. I use 6 turn and 4 x 470nF capacitors. How can it happen? Should I use 7812 to feed Gate? Can you show the drawing? Or wrong pin connection of FET? is it G, D, S if read from front side? Thanks
RMCybernetics - Sunday, 30th October 2011 11:01am - #4649
Rusdi,
There is also the temperature hazard, and then potentially chemical hazards if components get burned. The scope is not needed, but was useful for seing the waveforms and frequency. The scope ground should be the same ground as your PSU. you can then measure at the MOSFET gate, or collector terminals. If you measure at the collector, remember that the voltage could be much higher than the supply voltage so set the scope accordingly.
Surastyo.
I can't seem to find the datasheet for that part number. What are its ratings? They are typically set as GDS, but you need to check the manufacturers datasheet. I also do not see any large inductor (L2) in your picture. I've attached a diagram showing the 7812 voltage regulator being used.
Garudadidada - Sunday, 30th October 2011 8:51pm - #4650
DELETED: No sending of secret messages in Indonesian or any other language.
Surastyo - Monday, 31st October 2011 3:20am - #4652
FQP60N06: I think its 60V, 18A.its chinnese and hardly to find the data sheet. The large inductor (L2)is behind the CAPs. see my new pic. Thanks for 7812 diagram. I'll try another other MOSFET I have, while waiting the the order from RMCybernetics arrived. BTW what is modification needed to make it a "Induction Furnace" to melt aluminum (700 deg. C)? Thanks
RMCybernetics - Monday, 31st October 2011 1:06pm - #4654
I think 60V is much too low of a voltage rating for the MOSFETs. THey are probably being destroyed by over voltage.
To get hotter temperatures, you need to use more powerful transistors and capacitors, and then use a higher supply voltage.
Rusdi - Monday, 31st October 2011 5:10pm - #4655
This is something else to use this as an induction furnace, but could you recommend stronger caps and transistors and how about the higher voltage power supply? I'd like to buy them from you, rmc
Rusdi - Wednesday, 2nd November 2011 8:26am - #4656
Rmcybernetics, could u recomend some "higher" transistors and caps? I intend to buy some sets from u but I think ill go for the "higher" components if they exist in ur site and with ur recomendations.
RMCybernetics - Wednesday, 2nd November 2011 9:43am - #4657
We don't have anything else available at the moment. You would just have to look for components with larger voltage and current ratings.
Martin - Tuesday, 8th November 2011 3:42pm - #4659
I've tried building an induction heater based on your schematic and it works quite well. However, my heater won't heat up to 'glowing point' (maybe due to my power supply, it's only 30V, 5A) and, a bigger problem, my FETs tend to become pretty hot. When i look at my coil voltage with a scope it's way more noisy and irregular than what you are having. Do you have any clue about what might be going on here?
joco - Tuesday, 8th November 2011 4:33pm - #4660
FET's going warm....Amps...up like hell...what is going on? I used irfpb4615, 4 pcs of 330n capacitor...the rest the same as yours...oh...with a 25V supply.
RMCybernetics - Tuesday, 8th November 2011 6:24pm - #4661
Martin, If you are not getting nice sinusoidal oscillations, this could be due to having too little, or even too much inductance in your choke (L2). You may need to experiment with different choke designs to find something that works well with your other parts. Your work coil should ideally be only a little larger than the object to be heated as this will maximise the concentration of magnetic flux. If that does not help, add a photo of your scope showing the gate voltage, and drain voltage waveforms.
Joco, I can't find that part number. Did you make a typo?
Tohooloo - Tuesday, 8th November 2011 9:06pm - #4662
What is the maximum capacitance for C1.
joco - Wednesday, 9th November 2011 6:45am - #4663
sorry for part number. it's irfb4615
RMCybernetics - Wednesday, 9th November 2011 8:38am - #4664
Tohooloo, C1 can be as large as you like. The combination of capacitance of C1 and the inductance of L1 form a resonant circuit. A larger capacitance or inductance will result in a lower frequency.
Joco, That MOSFET seems ok. Try using a larger choke (L2).
deyan - Friday, 11th November 2011 11:35pm - #4666
To get faster heating do i need higher or lower frequency
RMCybernetics - Saturday, 12th November 2011 9:55am - #4667
Neither. You need higher power.
deyan - Sunday, 13th November 2011 5:59pm - #4668
i am usinga 12 volt 10 amp power suply my trnsistor are p50n06 R1 R2 the dides and L2 are the same as yours. Is my suply weak because i cant get i to gloing point and a nother thing my car are burning in about a minute or so they are reatetd for 250-275 volts what shuld i change to get better reasults? Thank you.
deyan - Monday, 14th November 2011 5:14pm - #4669
can i use a IGBT such as BUP203 as the transistors they are reated for 1000volts and if yes are there any difernces in the schematic?
Stephen - Thursday, 8th December 2011 8:35pm - #4680
What voltage rating are your capacitors?
RMCybernetics - Sunday, 11th December 2011 4:32pm - #4684
Deyan,
It sounds like your capacitors have too much internal resistance (ESR). You need something that is better for high power, they are typically much larger in size for the same capacitance value. There are many types of transistors that may work, but it is up to you to test if the ones you have are ok. I suspect that a high voltage IGBT will have too large of a voltage drop between collector and emmiter which would mean that the opposite transistor would not switch off properly. I used these 100V, 35A MOSFETs which worked well.
Stephen,
I used these 1000V, 330nF capacitors.
Rob - Monday, 12th December 2011 8:01am - #4686
I sent an email, but I think I should just ask here. Would these parts work for this project? : 240 OHM 5W 5% METAL OXIDE 1N4007 FDA69N25 N-CH MOSFET 250V 69A TO-3P FILM Capacitor 2UF 700VDC B32794D3205K Also, will this circuit be able to handle 55V at 10A (with upgrades)? -Cheers
RMCybernetics - Wednesday, 14th December 2011 11:59am - #4687
I can only suggest you follow the instructions given. If you use other components, they may or may not work. That is up to you to work out.
Surastyo - Friday, 16th December 2011 11:10am - #4688
Hi again I try new coil, new caps, and new Mosfet. I burtn 5 or 6 of mosfets, it's happen because I didn't realize that one diode is sorted so HV directly goes to G pin. Now I use 30A, 30V power supply, IRFP260, 6A diode, 7812, 7T copper pipe coil,etc.I am quiet happy with the result, but it seems take to long to heat a thing. I plant to melt aluminum with it. my question are: 1. is coil turn, coil diameter, capacitor size affect heating power, or it just shaping the wave? 2. my wave is slithly different from yours, why? 3. is it ok to increase the V+ to 50V or 90V to increase power (yes I'll count the mosfet and diode power rate) ? 4. how to trim this to be most efficient? is wave form can determine that? let say clear simetrical wave is most efficient? 5. can we create sinusoidal wave? 6. is sinusoidal wave the most efficient wave for induction heating? Ohh... I hope it's not to much.. Thanks
Surastyo - Friday, 16th December 2011 11:12am - #4689
it makes things hot 100 or 200 deg C maybe.. here the other picture
RMCybernetics - Friday, 16th December 2011 11:39am - #4690
1. All those factors will vary the performance. The number of turns will determine the impedance of the coil and therefore how much current will flow for a given frequency. Less turns will allow for higher peak current, but too few and the transistors will blow.
The coil diameter should ideally be just slightly larger than the workpiece that is to be heated. This maximises the field coupling and is more efficient.
The capacitor size will also determine peak current. larger is better, but not too large or the resonant frequency will become too low. Physically larger capacitors will have low internal resistance too so they will perform much better. The bank of caps in your picture look way to small for the amount of metal you are trying to heat.
2. You should get a nice half sine waveform. You need to experiment witht the inductor (L2). Try different numbers of turns until you see some improvement. You could also add 15V Zener diodes between the gate and source pins of each transistor to help protect them from voltage spikes.
3. V+ can be as high as you like, just make sure your components are sufficioent to handle the voltage rise in the coil. You will also need to supply the gates from a stable 12V source.
4,5,6. See other answers.
Nicollas - Tuesday, 20th December 2011 12:10am - #4691
Hello I wonder if VDC power supplies used to feed the coil L2 and Gates/MOSFETS are two power suplies separates.
RMCybernetics - Tuesday, 20th December 2011 11:08am - #4692
You can use a single power supply, or seperate ones. If using a single supply it should be at most 15V, or 30V if you use the regulator as shown in another post.
Nicollas - Wednesday, 21st December 2011 8:21pm - #4696
HELLO, MY HILL ​​LOOP, BUT WHEN PUT IN POWER SUPPLY CIRCUIT, He behaves like a short circuit and the voltage drops too, IF I DISCONNECT THE CENTER OF TENSION COIL Normalize, BUT NOT THE NOTHING HAPPENS
RMCybernetics - Friday, 23rd December 2011 10:50am - #4697
Your power supply is not able to deliver enough current. You need a bigger supply, or many more turns on the work coil or choke.
Rob - Sunday, 25th December 2011 8:40am - #4698
Will this circuit work properly with a power supply of 12v at 30A?
RMCybernetics - Wednesday, 28th December 2011 2:25pm - #4699
Yes
Nicollas - Thursday, 29th December 2011 8:55pm - #4701
I would like to know a way to reduce current consumption, because my source is 10 amps.
RMCybernetics - Wednesday, 4th January 2012 11:15am - #4705
The current will depend on the voltage you apply, and the load impedance. More turns on your work coil, smaller capacitors, and larger choke inductance will reduce current.
Rob - Thursday, 12th January 2012 5:01am - #4707
Just posting to share that I've successfully made my own heater using the info here. Some details of what I used: - ~.3uH work coil -12v 30A power supply -IRFB59N10DPBF mosfets -4.2uf capacitor bank (100A pulse) -2mH choke I posted a Video Response to the original video: http://www.youtube.com/watch?v=AT_lRjYjzUg -Thanks for sharing this information.
RMCybernetics - Thursday, 12th January 2012 2:33pm - #4708
Nice job. Thanks for sharing Rob.
james - Friday, 13th January 2012 11:00pm - #4709
Hello, Would it be possible for you to show a bit clearer picture of the physical connections of the transistors themselves and to also indicate which pins are what for the electronically challengened among us ?
Chanil - Saturday, 14th January 2012 12:56am - #4710
Hi, is it possible to run this on 15V at 1A? For my application I only need it to achive 200 degrees celcius. But it has to run for days or even weeks at a time(it's for worlds largest 3d ABS printer). I'm currently using every component that is recommended, but all of them are getting hot... I have already roasted a capacitor(used a wrong one, would it explain the rise in temperture of the mosfets?)In my tests I've powered them with a 19V 5A psu(Im using a 12v regulator for the gates). I'm planning to use multiple heatsinks with a small fan to provide cooling. So to conclude will it reach the required temperture if only using 15V at 1A? Will the components stay cool if it would work? And if not any suggestions?
RMCybernetics - Sunday, 15th January 2012 12:08pm - #4713
James,
If you Google the part numbers you will find the manufacturer pdf datasheets. These will tell you which pins provide a particular function. I think it is best you try working this out yourself as you will gain a better knowledge and understanding. You can also check out the section on the site for helping to learn electronics as it will explain a lot about the components and the physics of the electronics involved.
Chanil,
Yes, if you want to limit the current to 1A, then you must increase the impedance of the circuit. Using many more turns in your work coil and the choke will limit the current.
Chanil - Friday, 27th January 2012 7:21pm - #4719
Check out my induction heater ^^. http://www.youtube.com/watch?v=iTIHvc6AohI I had a board made for it. This is one of the tests for it. Note: the cam can't read higher temps than 270 degrees celcius. And for my application only 205-210 is required. It reaches about 400-500 degrees celcius in the video.
RMCybernetics - Sunday, 29th January 2012 9:38pm - #4722
Chanil's video...
akram - Tuesday, 31st January 2012 9:26am - #4729
I used power supply 110 volt 60 A i want to design a circuit i want to know the kind of mosfet transistor and diode and resistors and capacitors so we want a quotation for the material
justin - Sunday, 5th February 2012 11:16pm - #4731
hi guys i built this thing and had a little truble it turned out to be the diodes i was useing (4007) and changed them to some smaller glass ones (don't know what they are) and with 1.8uf worth of caps it works great!! it was a lot of fun and i built two more to give away all the parts i had got from a broken flat screen tv. they run around 125k and i used IGBT. thanks for the project and a good rundown on it!!!!!!
ad - Monday, 6th February 2012 4:27am - #4732
RMCybernetics, I really like your coil design! I'm working on a project where I need to have a tank that resonates at about 1 MHz. Do you have suggestions for modifying C1, L1, and L2 for that purpose? As long as the FETS can switch fast enough the rest of the circuit can likely remain the same; but I'm not sure whether I'm better of decreasing C or L to get the right resonance. if you had any references for choosing those values that would also be great! thanks, a.d.
Eric - Friday, 10th February 2012 10:22pm - #4737
I've noticed some interesting behavior with this circuit and I am curious what you think. I used all the same components (The coil is similar and the caps are similar, same mosfet, diodes and resistors (I did use a 124 ohm resistors as well, with similar behavior)). Using a 30V 30A supply the circuit pulls a lot of Amps (15 to 30A) at a very low voltage and the supply simply can't increase the voltage beyond a few volts. Using a 25V .5A supply the circuit draws power at a low voltage, but I can increase the voltage. At about 5V (according to the analog meter on the supply, could be different given the load) the resonant circuit kicks in and we get a beautiful sine wave on the resonant circuit (but minimal heating). Using this I went back to the large supply. I connected a switch between the supply and the circuit and set the supply to 12V. Flipping the switch (providing a near instantaneous 12V) drove the sine wave just as before (now pulling a bit more current as the supply could handle it). So there seems to be some issue at low voltages. It may explain why @joco was getting 'amps like hell' at low voltages.
RMCybernetics - Monday, 13th February 2012 4:57pm - #4740
ad,
You can reduce C, but you will need t make sure that the remaining capacitors you have are able to take all the current. The advantage of using lots of capacitors is that the current is shared between them.
Eric,
What you describes just sounds like it is due to the limitations of your PSU. Remember that voltage and current are directly related and will be affected by the impedance of your load. If your PSU shows low volts, and high amps, this indicates that the impedance of your circuit is low and your PSU is dropping the volts to keep the current within its ratings.
Eric - Thursday, 16th February 2012 1:24am - #4744
RMC, What is odd is that the circuit has very low impedance at low voltage (1-2 volts) and normal impedance at 12 volts. This is using the same circuit and supply in both cases. The only difference is that in the 12 volt case I immediately apply the full 12 volts via a switch instead of hooking up the supply and turning up the voltage. Using my low amperage supply I was able to see that the harmonic circuit wasn't kicking in until about 5V. My guess is that at low voltages the harmonic L-C system isn't being driven and the DC load is passing through a single mosfet through the coil. In this case the impedance would be very low. I have observed just a single hot mosfet in this odd low voltage scenario.
RMCybernetics - Saturday, 18th February 2012 3:52pm - #4748
Yes, it would seem that you just have DC flowing at low voltages
javier - Wednesday, 14th March 2012 4:01am - #4759
DISCULPA YO HE CONSTRUIDO UN TU CIRCUITO PERO NECESITO MANEJAR 110V Y 25A, PERO CUANDO CONECTO EL CIRCUITO A LA FUENTE LOS MOSFET EXPLOTAN, LOS MOSFET QUE USO SON DE 600V Y 40A. AYUDAME POR FAVOR ES MUY URGENTE SORRY I HAVE BUILT A CIRCUIT BUT I NEED YOUR DRIVER 110V and 25A, BUT WHEN THE CIRCUIT CONNECTED TO SOURCE THE EXPLOIT MOSFET, MOSFET THE USE THAT ARE 600V and 40A. PLEASE HELP ME IS URGENT
RMCybernetics - Wednesday, 14th March 2012 5:53pm - #4762
Your MOSFET needs to be able to withtsand the peak current. Measure the DC current your coil draws from your supply whehn you apply 120V. I suspect you need more turns on your work coil and choke.
david - Saturday, 17th March 2012 4:10pm - #4769
can you use 12 volts for this project?
Hampus - Thursday, 29th March 2012 12:42pm - #4771
Which one of the diods are you actualy using? The 40V or the 100V?
RMCybernetics - Friday, 6th April 2012 9:04am - #4777
David, yes.
Hampus, Both. The first version uses the 40V ones, later when more power is used, the 1000V ones are used.
Benjamin - Monday, 9th April 2012 12:59am - #4780
RMC, I have managed to reproduce your induction heater using the same components and circuit, but mine isn't working. I powered it with a 19V 4,5Amps laptop power supply. Actually, all the voltage is shared between the two resistors and it's like no current flows in the control circuit. Do you have any idea about where the problem could come from ?
Chris - Monday, 16th April 2012 7:54am - #4782
Hi there. I built a smaller induction heater following as closely as I could to yours, and after a few unfortunate accidents, i got it working and loved it. I am now upsizing to a 110 volt version from wall power rectified through a bridge and a transformer with rectifier for 12 volts to the gates. My question is can I solely use the choke to limit current so that I could have a one turn work coil if I wanted, and if so, do I add that impedance to half or all of the work coil as it is center tapped. Thank you for your great work
RMCybernetics - Monday, 16th April 2012 9:47am - #4784
Benjamin,
Maybe it is the 19V supply. Make sure you use a regulator for the gates as shown in a previous post.
Chris,
Yes the choke will limit the current, but only as long as it is oscillating. You should work based on the impedance of half the work coil.
MrLeeh - Wednesday, 18th April 2012 12:13pm - #4787
Dear RMCybernetics, dear users thanks for this smart and very simple way of inductional heating. I tried it and eventually it worked very well. We can heat things up to 350°C and higher. At first we had problems with the MOSFETS getting hot and also switching through at a certain power voltage level (around 8V). So we couldn' t get any more then 40W of heating power. Then we discoverred that the wires we used to connect the SOURCE to the ground were simply to long and at the high frequency they produced lot' s of noise. So we decided to use only one thick wire as connection to the ground of the source and part it short-wired to the two MOSFETs. Now we still got some noise on the GATE but it works very well (15V, 10A). Greetings MrLeeh
nathan - Sunday, 22nd April 2012 5:44pm - #4792
amazing project. cant wait to try it out. I've seen some posts about upping the power with larger caps and higher rated mosfets with larger power supply but is it possible to use more of the same mosfets just hooked in parallel with a larger power supply and caps or would that cause issues with the gates. I've seen it done in certain types of sound amps but I'm a little unfamiliar with high voltage mosfets and want to make sure before trying
RMCybernetics - Tuesday, 24th April 2012 12:27pm - #4794
It might be possible to parallel some MOSFETs, but you would need to make short neat connections otherwise they may suffer from interference problems.
Deven - Tuesday, 1st May 2012 4:21pm - #4795
which type of FET used in 30v 10A Supply in your second case, and give the dimention copper tube and redious of turn.
RMCybernetics - Tuesday, 8th May 2012 12:10pm - #4796
The STP30NF10 is used in both versions. We used 4mm brass tube, with a coil radius of 25mm.
Gilles - Wednesday, 6th June 2012 3:34pm - #4804
Hi, Is it possible and what would it take to have a dimmer switch controlling the intensity of heat?
RMCybernetics - Tuesday, 12th June 2012 2:39pm - #4805
You would need some type of interrupter circuit and then vary the pulse width of the interrupter. For example; You could use one of our Power Pulse Modulators set to a low frequency to supply the power to the circuit. Adjusting the pulse width setting would proportionally adjust the power in the heater.
Hans - Tuesday, 17th July 2012 8:46pm - #4807
Hi Would it be possible to use a welding AC "buzz box" whith a suitable bridge rectifier as a power source ? ( no load voltage 57 V and 25 V at 100 A) Or maybe a inverter welder? I wan't some type of transformer etc since I'm not to fond of hooking up the mains 240 V to a barbed wire !!! Hans
whisk - Thursday, 19th July 2012 7:08pm - #4808
I am trying to build a small version of this using 12v power supply but the solder used to connect the coil to the capacitors keeps melting. Any suggestions. I believe the circuit is working but I can't be sure since it only stays on a few seconds before the solder melts. Perhaps something else is going wrong. Should the coil be getting this hot?
RMCybernetics - Thursday, 19th July 2012 10:21pm - #4809
Hans,
You would also need a very large smoothing capacitor, but it could work.
whisk,
If your solder is melting so quickly it is probably because your wire is too thin. You need to make the coil from very thick wire or copper pipe.
wellington - Sunday, 22nd July 2012 1:22am - #4810
thanks for the info my question is if I can use this circuit to 24 volts from a battery or 110 volts i also used to reduce a source is 24v 0 30v please ci there is a change in the circuit please give me ce can also use more parallel trancistores
wellington - Sunday, 22nd July 2012 1:34am - #4811
irf150n MOSFET can be used, or income tax or 54n 64n tanbien the iprf250n for use in parallel bariums
RMCybernetics - Friday, 27th July 2012 12:33pm - #4814
wellinton, I do not understand you. If you are using an electronic translator, make sure to use good punctuation and grammar for an accurate translation.
Aamer - Friday, 27th July 2012 8:42pm - #4815
I am planning to make this simple Induction Heater for heating Catheter Tipping Molds. Please see the attached picture of the mold for your reference. I plan to heat two molds simultaneously. Mold diameter 1/2" and distance between the molds would be 4". I have 2 questions: a)Is it important to have 1000v capacitors? What minimum voltage rating would be OK? b)The second picture shows 4 designs of work coils. Which of them would be more efficient to heat both the molds.
Aamer - Friday, 27th July 2012 8:46pm - #4816
Here are the four designs of work coils. Ah yes, another question: Does a solid copper wire coil would do the job?
kevin - Saturday, 28th July 2012 12:20am - #4817
Hey Guys, Ran some calculations on both of your heaters. In the first one, at about 200kHz, the inductor should be about 1 uH. Realize that the peak voltage that is ringing in the tank circuit is going to be pi* supply voltage, in this case about 47v. This yields a peak current of about 39 amps! (27.5 RMS amps) Given that 2mm brass tubing was used, this give the cross sectional area of about 3mm^2, and since it was tubing, most likely about 1mm^2 for current to flow, the approx. size of an 18 AWG wire. Passing 27 amps through 18 gauge wire would heat the wire up to well over 90C if it was pure copper, so being brass would increase the losses and it shows in the photo where unloaded the circuit is dissipating over 40 watts! no wonder the coild was starting to soften. The second circuit is a little better. It is using 1.98 uF of capacitance at 133 kHz. This gives us a coil inductance of about 0.723 uH. This yeilds a current in a tank of about 105 RMS A. Even though the tubing is larger and cooled, the losses before inserting the load was already at 210W. That being said, the current ringing in the work coil needs to be reduced. That can be done by one of two means, increase the inductance or reduce the capacitance or both. i(t)=v(t) sqrt (C/L). This is derived by setting the reactive power formula equal to one another and solving. KVAR = V^2/Xc = I^2*Xl. I would redesign to limit the resonant current in the work coil to be much lower and then see what quiescent losses are. Then put in your load. I bet the time to temperature would be greatly reduce because more power is going into the load and not be wasted in circulating current loses. Kev
RMCybernetics - Monday, 30th July 2012 6:40pm - #4818
Aamer, a) The capacitors voltage rating just needs to be larger than the voltage they might be exposed to. Remember to account for the resonant voltage rise. b) A would not be very good due to low coupling, but the others will be ok. Copper wire is only going to be ok at low power levels. Litz wire would be better, but water cooled pipe will be best.
RMCybernetics - Monday, 30th July 2012 6:41pm - #4819
Thanks for your comments Kev.
grant - Wednesday, 1st August 2012 3:58am - #4820
I would like a to make one that uses no more than 12V and 10A what size of capacitors and resisters etc. do I need. I need it to vaporize gasoline or diesel fuel in a metal pipe thats about 1/4 in ID max. (Goal temps around 140-200 F) I'm very green at this I need a lot of help with this science project
RMCybernetics - Friday, 3rd August 2012 2:23pm - #4821
Grant, You need to work out the values for yourself, we can not do your project for you.
john - Sunday, 5th August 2012 7:04am - #4822
Thank you for your time to answer this question...Is it possible to make an induction heater that would heat pieces of iron that are welded to a rotating drum as the individual pieces pass over the induction coil with say, 10 pieces of iron distributed around the circumference of this drum, and be able to heat the drum by this method quickly to around 460 degrees, with a wattage of in excess of 3000 watts? Again thank you for the time to tell me if I am barking up the wrong tree. John
RMCybernetics - Monday, 6th August 2012 1:20pm - #4823
It depends on how fast it is rotating, and how large the metal parts are.
Aamer - Thursday, 9th August 2012 10:10pm - #4824
Comparing my last proposal of work coils - B, C, and D, what do say about this modification?
RMCybernetics - Friday, 10th August 2012 6:40pm - #4825
It looks OK. Is there any reason the tips cant be closer together, or even placed end to end? Separating the two halves of the coil means that the field in each coil will oscillating in strength, rather than alternating polarity as you would have when the coils are together. You would really be better off having two separate circuits and coils as it would be most effective.
Hans - Friday, 10th August 2012 8:17pm - #4827
Hi I was thinking about Kevins post. I'm not an EE and can be totaly wrong but : In a self oscillating circuit like this the freqency tend to be where the capacitive and inductive reactance equals out eatch other ie: the voltage and current is in phase and the power factor is close to 1 . If this is true, then the losses must come from resistive load ie the resistance in the coil and copper would probably be a much better material for the coil ? Since it is a self resonant circuit, changing cap or coil would alter freqency : more inductance or less capacitance = higher freqency and less inductance or more capacitance = lower frequency. Now to my question : If I am right, what benefits would there be if I used higher (or lower) freqency? Would I get higher effeciency ? If I am wrong, where did I go wrong? Hans
Justin - Saturday, 11th August 2012 7:57pm - #4828
Is there a risk of shock with this circuit? -risk of shock by touching the element that is being heated in the coil with another metal rod? (or is it electrically isolated?) -risk of shock/spark/dangerous short by touching the element to be heated to the coil? -risk of shock by touching the brass coil? -anything else i might not be thinking of?
RMCybernetics - Saturday, 11th August 2012 8:45pm - #4829
Hans, Most losses will come from resistance in the components. Mostly in the coil in this case, but losses in the capacitor are not insignificant. It is important to use capacitors with a low ESR. You have things a little mixed regards to altering frequency. Increasing either inductance or capacitance will lower the frequency. At higher frequency there will be more losses in the capacitor dielectric, and also in the coil due to the skin effect. The skin effect would also mean that at high frequencies the heating would be concentrated in thinner layers on the surface of material sample.
Justin, Yes, the voltage rises as described in the article would mean that exposed terminals or the coil could have high voltages present. You should avoid letting the heated object touch the coil as it could short circuit and damage your transistors.
wellington - Thursday, 16th August 2012 9:40pm - #4830
thanks for the design I did 12 volt and perfect design I am interested in a dipocitibo de24volts acer 110 volts and 220 volts mofet which I can use or would have k k using thyristors and the condenser capacities thanks for the design is very cool I worked for one time and I'm interested in Majorcan efficient voltage for faster heating
Nicollas - Friday, 17th August 2012 11:12pm - #4831
I set up a circuit like this. but he is not working. one of the mosfets is very warming and the current is very high. put 12V but the current one seems Curco circuit. aumeitei as the number of windings L1 and L2 no more works. nothing changes that. I'm using mosfet IRFP250N what might be happening? my source is 12V/20AMPS.
RMCybernetics - Saturday, 18th August 2012 11:30am - #4832
wellington, I have no idea what you are talking about. Nicollas, I do not really understand all you wrote either, but it sounds like your circuit is not oscilating. If you are also using different diodes, it could be because they have too much voltage drop which prevents the transistors from being switched.
Mike - Friday, 24th August 2012 4:38am - #4835
Can stainless steel be used for the work coil?
RMCybernetics - Friday, 24th August 2012 9:04am - #4836
No. The resistance of the coil would be too high. The losses in the coil would cause it to get very hot and waste a lot of power. Copper is the best material to use. Brass was only used here because we had the pipe in our workshop and it was small enough for making this simple demonstration.
Nicollas - Saturday, 25th August 2012 12:13am - #4837
swapped for new 1N4007 diodes and still does not work, the voltage drops to 12 volts to 6 volts, and does not oscillate. 'm using 220ohm resistors, it interfere in the functioning of the circuit?
Mike - Monday, 27th August 2012 5:33am - #4838
Ok, great,one more question. I'm using your same circuit and I'm using a 12v 16.7A switching supply is this going to be a problem? I hooked it up and seemed to fry my diodes. I'm using a nte2396 FET with enhancement mode. I ordered the ones your using to see if that's the problem. it also makes my supply go into protection mode, almost like the supply saw the curcuit as a dead short, I'm hoping it's the transistors, or perhaps I need a bigger work coil, any help?
RMCybernetics - Monday, 27th August 2012 8:06pm - #4839
Nicollas, Mike; Use the diagram in post 4649 that includes a voltage regulator. Use a bigger choke, and place a large capacitor parallel to the PSU to help it cope with current surges.
Mike - Wednesday, 29th August 2012 4:22am - #4840
That's good avice, A: is there a calculation that I can use to determine the inductance for L2 based on the inductance/resistance of L1? Im using 3/8 inch copper pipe. B: do I stll need a 12V regulator in the circuit if I'm using a single 12V supply to drive the whole thing?
Andreas - Thursday, 30th August 2012 12:33am - #4841
Hello. In advance, sorry about my poor English! We bougth a inductive heater at work a last week it cost about 1500 dollars, and i said that i was wondering about building one myself, so all the guys i work with laught at me and said i could not do it... So i desided that i had to do it to shut them up by building one! ;) but there is a few problems... I`m really not a expert on electronics but i have a mild understanding of it so i think i understand most of the shematic you have drew, exept on the right of the shematic there is someting called "L2". Can you maybe try to explain it to me? And the second question: I have a 22V power supply, If make the inductor just as you have shown in the first part of your DIY, exept i use My 22V supply instead of 15V, the Diodes that you used on the "phushing it further" part of the DIY, the thicer brass tubing and maybe 4 capacitors (or do i need 6 on 22V allso?) Would this work??? I thing its great that i can buy all the parts from your DIY on your page! Best regards!
Andreas - Thursday, 30th August 2012 10:28pm - #4842
Hello, I am going to use a 22V power supply, will i need the 12V voltage regulator mentioned in the diy? where do i conect it? Are the Mosfet`s marked so i know witch leg on the transistor goes where?
wellington - Sunday, 2nd September 2012 10:21pm - #4843
is okey 12 volts 110volts ?mosfet? wat number plees
RMCybernetics - Monday, 3rd September 2012 11:55am - #4844
Mike, Andreas, The inductor L2 serves as a choke to prevent high frequencies reaching your power supply, and also as a ballast to limit current. The calulations will depend on your operation frequency and desired current. 22V is fine, but you will need to feed the gates via a regulator as shown in a previous post. You should probably use more than four capacitors.
Andreas - Monday, 3rd September 2012 9:50pm - #4845
Hello again. I have ordered 8 capasitors from you, is it best to use 6 like you have on your setup or will it be best to use them all?
reg - Friday, 7th September 2012 3:03pm - #4849
i make your schematic and it works very good! thanks just one question, my mosfets are very hot why ? thank you for answer
RMCybernetics - Friday, 7th September 2012 3:47pm - #4851
Andreas, 6 or 8 will work OK. Using 8 may share the current a little more and therefore not heat up so much. Reg, the temperature of the MOSFETs will depend on the current flowing and the frequency. If the frequency and current is quite high, it is normal for them to heat up. Try using a larger heatsink, or MOSFETs with a lower drain-source resistance.
reg - Friday, 7th September 2012 3:58pm - #4852
thanks for your answer i use mosfet irf 540, use 36V power supply and separate 12V supply for vgs 10 + 10 turns work coil with 680 nF capacitor 1000V , L2 2O turns it is good?
RMCybernetics - Friday, 7th September 2012 4:50pm - #4853
See the calculations posted by kevin in post 4817. With a 36V input and IRF540 transistor you are likely to blow the transistors. As shown in the article our 30V input was causing it to push close to the limits of the transistors used.
reg - Friday, 7th September 2012 6:06pm - #4854
ok ,i will try 25 volts power supply and greater heatsink , thank you for your fast answer bye...
reg - Tuesday, 11th September 2012 5:18pm - #4856
hello , do you know what it happen if the gates becomes less than 12V?
Nicollas - Wednesday, 12th September 2012 7:20pm - #4857
I am very pleased with the outcome of my induction heater. after many failed attempts I managed to solve the problem and now it works fine. Thank you all for the help.
Waheed - Thursday, 13th September 2012 12:11pm - #4858
Thanks for useful information. My circuit consists of IRF3710, 5x330nF/100V caps, 4 Turns of 3mm OD tubing at 12V. Draws 4 Amps. Tried it on higher voltage using 7812 but didnt work - no oscillation. Removed 7812 but with a large object in coil the current shoots up uncontrollably, burning FETs. What could be the reason. Thanks
Waheed - Thursday, 13th September 2012 12:13pm - #4859
Just wanted to show the waveforms.
RMCybernetics - Thursday, 13th September 2012 2:00pm - #4860
reg, if the gates are not switched on with a high enough voltage, the transistors will heat up significantly. Waheed, adding a large object in the coil will increase current demand a lot. if you want to limit the current, use a bigger choke (L2).
Aamer - Friday, 14th September 2012 6:17pm - #4861
For the choke L2, can a straight ferrite bar be used instead of toroidal core? For the capacitor bank, is it OK to use 28 x 68nF (400V)?
Aamer - Monday, 17th September 2012 2:47pm - #4862
Here is the work coil which I have designed for my application. I would like to know how shall I join the two ends encircled in red color for continuous flow of cooling water? Do I need to braze them with brass or simply connect them with PVC tube?
RMCybernetics - Tuesday, 18th September 2012 6:00pm - #4864
A straight bar is ok, but will need more turns compared to a toroid. Those caps should be ok as long as they are capable of withstanding large currents and high temperatures. You can just link the ends using some PVC pipe as long as the copper is connected together too.
Daniel - Wednesday, 19th September 2012 4:09pm - #4870
Hi I would like to make one that is about 500W Parts I have used: IRFP4768 transistor 1N4007 diodes 240 ohm resistor 12 turn work coil 7x0,15uF (total of 1,07uF) low ESR capacitors. About 2mH choke The powersupply is a 10A 30V lab supply. I use quite a big capacitor bank on the output of the powersupply to help it cope with the current surges. The problem is that when I crank up the voltage the transistor gets worm and shorts out (drain/source) I suspect it has something to do with the hairy coil since wave (blue trace)? I cannot figure out how to get rid of that noice, so i would really appreciate any help I can get on the subject. I tried mounting 12V zener diodes to protect the gate but haven't dared turning up the voltage again while the hairy sine wave is still there. I am on my last set of transistors. Thank you for sharing sutch a good project with us, and helping us all out.
Daniel - Wednesday, 19th September 2012 4:10pm - #4871
Here is a picture of the setup, I did not have my good camera here, so I can take a better picture later if that helps.
RMCybernetics - Thursday, 20th September 2012 10:17pm - #4873
Try using a much much bigger choke, and regulating the voltage used to feed the gates. Make sure the supply to the gates is well regulated and filtered.
grant - Sunday, 23rd September 2012 10:41pm - #4879
where did you get the radiator from?
Steve - Monday, 24th September 2012 3:05pm - #4880
What voltage should the 2uf capacitor be rated for? 15 V or 90 V?
RMCybernetics - Monday, 24th September 2012 10:15pm - #4881
Grant, The radiator is a modified CPU cooler from a computer. I think this one came from an old DELL PC.
Steve, The voltage rise in the circuit will be about 3.14 times your input voltage. But your capacitors voltage rating should be significantly larger so that they are not being pushed to their limits. I would suggest using one rated for at least 6 times your input voltage.
Andreas - Monday, 24th September 2012 11:14pm - #4882
Hi. I buildt a Induction heater. I used the same components as you, so you know the specs off the transistors, capasitors, voltage regulator, resistors and diodes. My induction heater will not heat any thing and the transistors heat up really fast? They are mountet on heatsinks... what can be wrong here? My coil is maked from brake lines, i have allso tried whit mutch thiner wiers... Would it help if i uploaded a picture?
RMCybernetics - Tuesday, 25th September 2012 12:16am - #4883
Are brake lines stainless steel? That has a high resistance, as do thin wires. You need to use thick cable or pipe that is highly conductive.
Andreas - Tuesday, 25th September 2012 11:46pm - #4885
The wire i used vas about 1,5 mm2... do you think that`s the problem?
Aamer - Friday, 28th September 2012 10:08am - #4886
Just to have everything in perfect order, here is the choke which I made with 2mm, SWG no. 14 copper enameled wire. Is it OK? The 28 x 68nF capacitors which I have mounted at the end of the work coil are MYLAR capacitors rated 400V but they are small size about 12mm x 8mm x 3mm. I wonder if they would do the job or should I replace them.
RMCybernetics - Friday, 28th September 2012 1:40pm - #4887
Looks ok. You can try the caps you have but they may overheat quite easily.
Andreas - Friday, 28th September 2012 11:21pm - #4888
hi, can anyone see any thing wrong whit this setup? this is my second inductor, but i am having the exact same problem... mosfets are getting real hot real fast? any ideas?
RMCybernetics - Saturday, 29th September 2012 1:09pm - #4889
Looks ok, but dont let your heatsinks touch together or you will just be causing a short circuit. Fit a capacitor to the output of your regulator too, that will help smooth out any noisy power line. Something like 330uF or more.
Daniel - Saturday, 29th September 2012 2:01pm - #4890
Hi I have tried different size inductors for L2 and it dosn't really seem to do any difference for the high frequency that is superimposed on the sinewawe. The biggest inductor I tried was about 40mH, The voltage in the LC circuit went down, but other than that there was little difference. I also have problems with the voltage spike in the beginning of the sine wawe being about double the voltage of the top of the sine.
Andreas - Monday, 1st October 2012 8:59pm - #4891
I cant get this to work... the non of the conections or heatsinks are touching. Here is a picture the wiering, are the diodes the right way, have i solderes them to the right legs on the transistors?
RMCybernetics - Monday, 1st October 2012 9:59pm - #4892
Daniel, Andreas,
Make sure the supply to the resistors is regulated and smoothed with a capacitor.
Check that your supply is capable of providing the peak current demanded by your coil.
Decouple the supply to the gates by placing a capacitor from 12V to GND while keeping the connections as short as possible.
Place a 12 to 15V zener diode between the gate and source of each MOSFET (cathode to the gate). This can help reduce noise and protects the transistors.
Aamer - Thursday, 4th October 2012 7:18pm - #4894
I have assembled the parts listed below as shown in the photo: MOSFET - STP30NF10 - 2 Pcs with Heatsinks DIODES - 1N4007 - 2 Pcs CAPACITORS - 330n x 6 (1250v) RESISTORS - 240 Ohms CHOKE L2 - SWG 14 (2 mm) Copper Wire 8 turns PSU - 12V 30A regulated, smoothed I switched ON the PSU for a few seconds, the MOSFET M1 in the photo started getting hot so, I switched OFF. Need your further assistance, please. One thing, the PSU is connected thru 50cm wires.
RMCybernetics - Friday, 5th October 2012 11:34am - #4895
Try replacing your choke with something with huge inductance so that power is limited significantly. You can use an ordinary mains transformer for this. Just use an output winding as the choke. If it still wont oscillate, make sure you don't have a dud transistor or diode somewhere.
Aamer - Friday, 5th October 2012 3:52pm - #4896
Before replacing the choke I checked the MOSFETs and found that my all the pins of my M1 are short. For M2, while connecting the negative probe of multimeter (on diode checking mode) to the center pin (DRAIN) and the positive probe to the left pin (GATE) the multimeter beeps for continuity. And touching the positive probe to the right pin (SOURCE) the multimeter shows 490. And if connecting the pins vice versa then no continuity. I can understand that M1 is bad but not sure about about M2. As for replacing the choke with an ordinary transformer, do you mean I can use secondary winding of any 220->3v, 6v, 9v, 12v transformer (less than 1 Ampere)?
RMCybernetics - Friday, 5th October 2012 4:39pm - #4897
You should just replace both MOSFETs in your induction heater to be sure. Yes, pretty much any low power transformer will have enough inductance to limit the current to a couple of amps or less. It will be useless for significant heating, but allows you to test if it is oscilating without blowing components. You may also want to add zener protection to the transistor gates.
Frank - Saturday, 6th October 2012 12:59am - #4901
Couple questions. 1. Obviously if you push the voltage up, the Mosfet gate must be protected with a reg, but where are you putting that because it appears you are shorting the drain and gate?? 2. You mention using alt caps for this. Would I need the lowest ESR caps possible? IE poly or film/foil caps? 3. There was a question above regarding tubing choice. It would seem that copper might be better for this. Is that accurate? Why did you select brass?
RMCybernetics - Saturday, 6th October 2012 9:20am - #4902
See post #4649 for a diagram including a regulator. Yes, the capacitors in your induction heater must be low ESR otherwise resistance losses will soon heat them to destruction. Yes, copper is better due to lower resistance. Brass was used simply becasue we had some available at the time. I've since built one with copper which I will post later, but I did not see any noticable performance difference and the heater coil still needed to be water cooled.
Paul - Saturday, 6th October 2012 11:06pm - #4903
Hi, Just an experimenter in electronics but think I will have to try this! Two questions 1) I see people generally heating iron or steel. Are there other common materials which might heat even more efffectively and is there a simple answer to predict which materials will heat well (I am guessing high permeativity, high hysteresis?) 2) Is the heating effect uniform throughout the interior of the coil? Or is it concentrated more towards the center or periphery? Lets say you were trying to heat the water in the copper tubing, would a hollow metal tube fit to the diameter of the coil work? Well I guess that is more than two questions, In any event thanks this looks like a great project.
RMCybernetics - Sunday, 7th October 2012 12:25pm - #4904
Iron based metals heat well because of hysteresis losses and conduction losses. Metals like copper and aluminium can be more difficult to heat partly due to higher conductivity.
The magnetic field is strongest at the inside edge of the coil. The skin effect also forces heating to concentrate on the surface of a material.
Aamer - Monday, 8th October 2012 3:02pm - #4905
I have replaced the MOSFETs. And also have replaced the choke with a low power transformer. I do not have an oscilliscope so how do I know if the circuit is oscillating or not.
RMCybernetics - Monday, 8th October 2012 3:19pm - #4906
Place something metal in the coil and see if it gets any warmer.
Frank - Monday, 8th October 2012 5:47pm - #4907
RM, Thanks for the reply regarding the voltage reg. I did notice the diagram with the 7812 but thought it was imcomplete because the drains of each mosfet still feed back to the gate of the other after the voltage reg. I was wondering if this should be done with two regs, both right at the gate and after the diodes? Just not sure how this configuration will work?
Aamer - Monday, 8th October 2012 9:32pm - #4908
Okay, I have made the test replacing the choke L2 with a low power transformer. Initially, the work coil became warmer and warmer so I circulated water in it. Finally I was able to notice that the iron rod inside the coil has become warm. However, when I replaced the transformer with the choke L2, the MOSFETs became hot quickly. And nothing happened to the iron rod inside the work coil. By the way, I haven't yet introduced zener protection for the transistor gate.
RMCybernetics - Tuesday, 9th October 2012 7:46pm - #4909
Frank, The diagram is ok. You should only use one regulator. The way the connections switch on and off the gates is described in the article.
Aamer, Show us your work coil and iron rod.
Aamer - Tuesday, 9th October 2012 8:58pm - #4910
You can see the work coil at post no. 4862. You can see the circuit at post no. 4894. The iron rod was not a particular one. I tested on an iron nail, an 8mm iron rod and 5mm rod.....all three got warm.
RMCybernetics - Wednesday, 10th October 2012 5:05pm - #4911
I still think you need a bigger choke. The huge inductance of the transformer winding is allowing it to oscillate, so you just need to find the right iinductance value for your setup. When powering up the induction heater, I would suggest that you do so without any metal within the coil, then add the metal after.
Aamer - Wednesday, 10th October 2012 6:22pm - #4912
Do you mean I should increase the number of turns in my choke shown in post no. 4886? How many more turns do you suggest? How do we find out the matching coil size other than actual trails? By the way, does every new circuit we build (with same parts) needs different choke setting (inductance)?
RMCybernetics - Wednesday, 10th October 2012 8:01pm - #4913
Yes, I think you will need to experiment with what works best with your specific PSU and heating coil. You could also try using a Power Pulse Modulator between your PSU and the induction heater circuit. This would allow you to vary the power to the heater. You woild set the frequency settng to a low value like 20 Hz, then you can adjust the duty setting from 0 to 100% to give you a 0 to 100% adjustment in heating power.
paul - Sunday, 14th October 2012 10:12am - #4917
Hi. I did exactly as instructed here and used all the same components but mine doesnt seem to work. Only one mosfet gets really warm. The PSu which was initially set to 15v and 5 amps drops to below 5 volts once the control circuit is connect. Any idea on what seems to be the problem? The PSU is rated at 30V and 10A. Thanks.
RMCybernetics - Sunday, 14th October 2012 2:59pm - #4918
Your PSU is not able to meet the peak current demaned by your setup. When you first connect power, there will be a surge of current which is mostly limited by your choke (L2). Use a bigger choke, and add some large capacitors to your PSU.
Aamer - Monday, 15th October 2012 7:07pm - #4919
I increased the size of choke L2 from 8 to 9 turns. It increased the amperes and blew off 30A fuse of my PSU. Now, as per your suggestion to introduce Power Pulse Modulator, I have just finished the "SQUARE WAVE SIGNAL GENERATOR WITH PULSE MODULATION" for my Induction Heater. I am confused how would it withstand heavy amperes. Please guide me how should I use it so that I can tune my Induction Heater.
RMCybernetics - Tuesday, 16th October 2012 12:05pm - #4921
See the troubleshooting section I've added to the end of the article. You don't tune your induction heater. It automatically works at the resonant frequency. The link I gave you is to a product which will allow you to limit and control the input power so that you do not blow your transistors while testing it. I don't think adding another DIY circuit is going to help you, as it just increases complexity. Adding 1 turn to your choke is going to make little difference. Add something like 20 turns. I really do not think there is anything else left to suggest to you. If you are following the article and all the advice, but it is still not working, then you must have faulty parts, wrong connections, or a PSU that is not up to the job.
Allen - Saturday, 20th October 2012 11:42am - #4922
Since you guys have a bit more experience then myself with induction heating devices, I wanted to ask how well might an MTY100N10E N ch. Mosfet work for an induction heating application as far as the drive transistors? This transistor is rated for 100A @ 100v the on-resistance is quite low as well @ 0.011ohms, the only thing I see that is quite different from the recommended transistor pair, is the switching times (rise / fall) are quite a bit higher, but I suspect that to be normal for such high currents possibly? I'd like to get some feedback from someone with a bit more experience to see if I can use these transistors for my induction heating tests. I'm interested in heating a bit larger objects and a bit faster. Thanks -Allen
RMCybernetics - Saturday, 20th October 2012 12:10pm - #4923
While I can't comment on every individual transistor model anyone might use, I can suggest that if you use one with longer rise/fall times, you could compensate by using a larger capacitance to lower the resonant frequency of the system.
Allen - Saturday, 20th October 2012 7:41pm - #4924
Is there a ratio of rise / fall times to capacitance values? I'm curious to know the mathematics behind the circuit.
RMCybernetics - Saturday, 20th October 2012 8:44pm - #4925
It only becomes an issue if the rise/fall times are a significant value compared to the period of the operating frequency of the circuit. The transistors are switching when the voltage (between source and drain) is almost zero. Just work out what the switching time is as a percentage of the period. By minimising this value, the switching losses are reduced. In this circuit you would probably be more concened with conduction losses due to high currents unless you need it to operate at some very high frequency for some reason.
Joe - Monday, 22nd October 2012 9:49am - #4927
Hi...I have been looking for a circuit like this wit a straight forward explanation..Kudos RMCybernetics. Will the caps (pictured) work with this project. .003uF 4Kv (302K4M) I am seeing in my calculations that my project will resonate near 400Khz. And if I am right, not an engineer, would mean I can heat larger objects.
RMCybernetics - Monday, 22nd October 2012 1:42pm - #4928
No they wont. That looks like a polystyrene capacitor and judging by the thickness of the wires, it is not meant for high currents. You need to use polypropylene capacitors or an equivalent that is specifically made for high currents. For larger objects you need more power.
Joe - Monday, 22nd October 2012 7:02pm - #4930
Thank you, I had guessed they werent going to work..wanted to ask before I released the magic smoke out of them
Joe - Tuesday, 23rd October 2012 8:07pm - #4931
Last question: What is, if any, the difference between polypropylene and mylar caps?
RMCybernetics - Wednesday, 24th October 2012 4:05pm - #4932
This link should answer that for you.
Aamer - Thursday, 25th October 2012 10:07am - #4933
Good day Richard.....Appreciate your devotion to guide others. Just for reference, I posted my Work Coil design at #4862 and the choke at #4886. I had to replace one faulty STP40NF10 with IRFP150. Now my circuit is oscillating with STP40NF10 + IRFP150 but the trial load (4mm iron nail) only gets warm. As per your advice, I re-designed my choke with 20 turns of 2mm wire and then reduced gradually 18, 16, 14, 12, 11, 10, 9, 8, 7, 6, 5 turns but no significant change. However, at 9-8-7-6 turns the load got warmer + the STP40NF10 dispersed more heat. By the way, I inserted the load for 5-10 seconds.
Aamer - Thursday, 25th October 2012 10:16am - #4934
Another question: I want to understand the behavior of this circuit and hence plan to simulate it in LTspice. How should I check if my simulation is correct......I mean to say, at what points I should check for the waveforms and what type of waveforms?
RMCybernetics - Thursday, 25th October 2012 1:43pm - #4935
You should allow more time for your load to heat up. I've added a spice simulation to the article just above the troubleshooting section. The STP40NF10 was not in the library so I just chose something else in the library. Run the simulation then check out the collector waveforms and inductor current. The simulation does not include any load, but you can add this if you wish. I'm not here to answer questions on how to use LTSpice though.
Aamer - Thursday, 25th October 2012 2:31pm - #4936
As per my results on various turns of the choke, the intensity of heat (as I felt) was almost the same. Of course, keeping the load for more time will make it hot. But, pardon me, my trial load is not thicker than the screwdriver shown in your article, which turned red hot in just 5 seconds.
RMCybernetics - Thursday, 25th October 2012 3:34pm - #4937
You are using different components and some kind of DIY power supply. You will of course not get the same results.
Aamer - Thursday, 25th October 2012 8:34pm - #4938
Thanks for your swift response. Okay, I shall change the STP40NF10 to IRFP150 and then re-try with my existing PSU which is functioning quite OK. But, I shall definitely not ignore your tip to change the PSU. By the way, what do say about the 12V 30A SMPS, will it be OK?? Your netlist could not be simulated because LTspice is giving an error "Multiple instances of Flag". Would you please check it. Thanks for your attention.
RMCybernetics - Thursday, 25th October 2012 11:22pm - #4939
Lol, the spice file is fine, I really don't know what you must be doing. You will need a higher input voltage than 12V to get heating like shown in the video (I used 30V). Have you also considered that your capacitors may be damaged, or just not up to the job?
Aamer - Friday, 26th October 2012 12:08pm - #4940
I have limited knowledge/experience of electronics. I am simply following the instructions as well the experience of other fellows. I knew you used 30v 10A. But you also confirmed in post #4698 that the circuit will work with 12v 30A PSU, and Bob was successful (post # 4894). Anyway, I can increase the voltage to 24V at 30A, will it be OK? As far as the capacitors are concerned, frankly, when the circuit is oscillating, I understood that the caps are working fine. I will try again with 24v, if unsuccessful then will check the caps. I renamed the spice file extension to "*.cir" and opened it in LTspice and then clicked RUN icon. If you think I am wrong, can you provide the "*.asc" file??? Lastly, thanks for your guidance.
Nicollas - Sunday, 28th October 2012 1:07am - #4941
This is the result obtained by me. was very good and oscillates at frequency of 75kHz. Thanks for the help RMcybernetics and friends.
Charles - Sunday, 28th October 2012 2:12am - #4942
> > > > two questions < < < < 1. In a water cooled installation would one still need brass induction coils instead of plain copper tubing? 2. I see where the coil configuration can be modified. So for tempering knives one could have an egg shaped coil allowing 1/4" clearances on all 4 sides. Correct? . . .thank you chas. ps. great site.
RMCybernetics - Sunday, 28th October 2012 2:52pm - #4943
Aamer, It is already an asc file. I don't know why you renamed it. Yes 12V will work but of course less powerful than 30V. As mentioned multiple times, the capacitors need to be quality polypropylene or equivalent. It may oscillate when using other caps, but the performance will be poor. If they are damaged by voltage spikes, that will also prevent proper operation.
Nicollas, Thanks for sharing. Nice build quality.
Charles, please read through the other comments. As mentioned already, brass was only used because it was available at the time. Copper pipe would be better. Yes you can use whatever coil shape you like. However the heating effect may not exactly match the shape as the magnetic interactions and shape of the object will dominate the effect.
ad - Tuesday, 30th October 2012 10:20am - #4944
Hello i build you heater, and it works ok....Now i want more power....but i hav one question... If i use bigger FET's / IGBT,up to 600v and 150A (MG150Q2YS40).. Can is use the same diodes to the gate, i think the power over the gates will be more than 20 volts....
RMCybernetics - Tuesday, 30th October 2012 11:13am - #4945
You can not just replace the transistors with power IGBTs. The saturation voltage of the transistors would be too high, preventing proper switching as explained in the article. A different and more complex circuit would be needed.
Aamer - Tuesday, 30th October 2012 2:14pm - #4946
Hi Richard. (1) The link for simulation opens NETLIST in another window which deceived me that you are providing netlist instead of asc file. Anyway, I have opened your asc file and compared with mine which wasn't simulating. The main difference was that you used 2 power supplies. Now my simulation results are same as yours. (2) In the simulation, I noticed that the circuit (except the capacitors and inductors) is drawing less than 1 Amp. So, I physically connected 12v-2A supply to the MOSFETs and 12V-30A to the choke. No oscillation, one MOSFET burnt. Maybe no oscillation because MOSFET burnt. Am I wrong somewhere? I plan to use 24v-30A for the choke and 12v-2A for the MOSFETs. (3) Mosfets IRFP150 + 6 x 330n Polypropylene Caps still oscillating at 12v-30A (but not red hot). Shall I use 24v-30A supply and add 7812 for the MOSFETs?
RMCybernetics - Tuesday, 30th October 2012 2:46pm - #4947
The link is directly to an asc file. You can click to view it, or right click and save it to your computer.
The simulation does not include any load and is not accounting for the losses in the system which is why it only draws a low current. You should observe the voltage on the 30V supply. During the first moments it will drop very low which could prevent oscilation in a single supply system if not accounted for. You should also consider the initial voltage spike as this could blow any of your components. Try this simulation. It will not oscilate becasue the PSU has too much internal resistance. Run it, you will only see DC, then alter the resistance to something lower and you will see it begins to oscilate.
Yes, add the regulator and zeners as suggested.
IntroductionInduction加热是一种非接触式加热过程。它使用高频电加热材料的导电。因为它是无触点,加热过程不污染物料被加热。它也是非常有效的自热实际上是内部生成的工件。这可以与其他加热方法生成的热量在火焰或加热元件,然后应用到工件。由于这些原因感应加热有助于一些独特的应用在工业上。
感应加热是如何工作的?一个源的高频电是用于驱动一个大的交变电流通过线圈。这个线圈被称为工作线圈。看到这幅画相反。通过电流通过线圈产生一个非常强烈的和快速变化的磁场在空间内的工作线圈。需要加热的工件放置在这强烈的交变磁场。根据工件材料的性质,许多事情发生…
交变磁场引起的电流在导电工件。安排的工作线圈和工件可以被认为是一个电子变压器。工作线圈就像主,电能是美联储,工件就像一个单匝的二次,是短路。这将导致巨大的电流流到工件。这些被称为涡流。此外,高频率用于感应加热应用程序产生一个现象称为趋肤效应。这集肤效应迫使交流电来流在一个薄层对表面的工件。皮肤效应增加了有效电阻的金属通道的大电流。因此该方法极大地提高了加热效应所引起的电流感应的工件。
(尽管加热由于涡流是可取的在这个应用程序中,有趣的是要注意,变压器制造商竭尽全力避免这个现象在他们的变形金刚。层压变压器铁芯、铁粉芯和铁氧体都是用来防止涡流流入变压器铁芯内。在一个变压器通过涡流是非常不可取的,因为它会导致加热的磁芯和代表力量,是浪费了。)
和黑色金属?对黑色金属如铁和某些类型的钢,有一个额外的加热机制发生的同时,涡流上面提到的。强烈的交变磁场在工作线圈和de-magnetises反复magnetises铁晶体。这种快速的翻动的磁域导致很大的摩擦和加热内部的材料。由于这种机制是加热称为磁滞损耗,是最大的材料,有大片的土地在他们的磁化曲线。这是一个大因素在感应加热所产生的热量,但仅发生在黑色金属材料。因为这个原因黑色材料借给自己更容易通过感应加热比有色金属材料。有趣的是,我们注意到其磁性钢失去大约700°以上加热时C。这个温度称为居里温度。这意味着超过700°C,不可能有加热的材料由于磁滞损耗。任何进一步的加热的材料必须是由于感生涡电流孤独。这使得超过700°C加热钢的挑战感应加热系统。事实上,铜和铝都非磁性和很好的导电体,也可以使这些材料热有效地挑战。(我们将会看到,最好的行动过程的这些材料是频率夸大损失由于集肤效应)。
感应加热是什么用的?感应加热可以用于任何应用程序,我们想热导电材料在一个清洁、高效、可控的。一个最常见的应用是为密封的防篡改海豹被卡到顶部的医学和饮料瓶子。一个箔密封涂有“热熔胶”是插入塑料帽和螺纹到顶层的每个瓶在制造。这些箔密封然后快速加热下的瓶子通过感应加热器在生产线上。所产生的热量融化胶和海豹的烘托到在瓶子的顶部。当盖被删除,箔仍然提供了一个密封的密封,防止任何篡改或污染的瓶子的内容直到客户穿透箔。另一个常见的应用程序是“getter发射“消除污染从疏散管如电视画面管、真空管、和各种气体放电灯。一个环的导电材料称为“getter”放置在疏散玻璃容器。自感应加热是一种非接触过程中,它可以用来加热getter,已经在一个密封的容器。一个感应工作线圈靠近getter外面的真空管和AC电源打开。在几秒内启动感应加热器,吸气剂加热白热,化学反应在其涂层与任何气体在真空。结果是,任何剩余的吸气剂吸收微量的气体在真空管,提高了纯度的真空。
另一个commonapplication对感应加热的过程称为带净化使用在半导体制造行业。这是一个过程中,硅ispurified通过一个移动的区熔材料。互联网搜索问题出现在这个过程的更多细节,我知之甚少。其他应用包括熔炼、焊接和钎焊或金属。Inductioncooking滚铣刀和电饭煲。金属淬火的弹药,齿轮的牙齿,sawblades和传动轴等也是常见的应用程序,因为inductionprocess加热表面的金属非常迅速。因此它可以用来forsurface硬化,硬化的金属部分的局部地区由“逃脱”热热传导深入部分稀稀拉拉的周边地区。非接触感应加热的性质也意味着它可以用于热材料在分析应用没有riskof污染标本。类似,金属医疗器械可能besterilised通过加热到高温,而他们仍然sealedinside已知的无菌环境,以杀死细菌。
什么是需要forInduction加热吗?理论上只有3样东西是必要的来实现感应加热:源的高频电源、工作线圈产生交变磁场,导电工件被加热,虽然这么说,但实际的感应加热系统通常是一个小工作更加复杂。例如,一个阻抗匹配网络往往是必要的一个通道高频源和工作线圈为了确保良好的powertransfer。水的冷却系统也普遍在大功率感应heatersto消除废热从工作线圈,其匹配网络和电力电子领域有着。最后一些控制电子产品通常是用来controlthe强度的加热作用,和时间来ensureconsistent加热循环的结果。控制电子也能保护神经系统由大量的不良操作条件。然而,基本原理的运作任何感应加热器仍describedearlier一样。
实际implementationIn实践工作线圈通常是纳入一个谐振回路电路。这有许多优点。首先,它使要么当前或thevoltage波形成为正弦。这最小化损失在逆变器byallowing它受益于要么零电压开关orzero-current-switching取决于确切的安排选择。Thesinusoidal波形在工作线圈也代表了一个更纯粹的信号andcauses少射频干扰到附近的设备。这之后pointbecoming非常重要的高性能系统。我们会发现有许多谐振计划的设计师一个感应加热器可以choosefor工作线圈:串联谐振回路circuitThe工作线圈是在预期的操作频率产生共鸣,我们一个电容器放在系列它。这使电流通过线圈的工作组是正弦。该系列共振也放大了voltageacross工作线圈,远高于单独的逆变器输出电压。看到一个正弦变频器负载电流,但它必须携带完整的currentthat流在工作线圈。因为这个原因工作线圈通常由金属丝只其实转几安培或数以安培流动。Significantheating功率是通过允许谐振电压上升的workcoil系列共振装置同时保持电流通过thecoil(逆变器)以一个合理的水平。这样的安排是常用的东西像电饭煲,powerlevel低,和逆变器位置紧邻对象需要加热。本系列的主要缺点是,逆变谐振安排mustcarry相同的电流流入工作线圈。除了这thevoltage上升由于串联谐振可以变得很明显如果有背板明显大小的工件出现在工作线圈抑制电路。这不是一个问题在应用程序像电饭煲,工件总同样的烹饪容器,它的属性是众所周知的在一次次的设计系统。坦克电容器一般是额定为高电压的电压升高theresonant因为经验的系列调谐谐振电路。它mustalso携带完整的电流由工作线圈,虽然这不是一个问题istypically在低功率应用程序。
平行resonanttank circuitThe工作线圈是在预期的操作频率产生共鸣,我们一个电容器放置在与它。这使电流通过线圈的工作组是正弦。并行磁共振也放大了currentthrough工作线圈,远高于输出电流能力的theinverter孤独。看到一个正弦变频器负载电流。然而,比如这件事它只有携带的部分,实际上realwork负载电流。这个逆变器不需要携带完整的循环电流在线圈的工作组。这是非常重要的因为功率因素在感应heatingapplications通常是低的。这个属性的并联谐振circuitcan让一个十倍减少电流,必须由theinverter和电线连接到工作线圈。传导损失通常与电流的平方,所以减少10倍loadcurrent代表一个重要的储蓄在传导损失inverterand相关的布线。这意味着工作线圈可以放置在alocation远程从逆变器不引起巨大的损失feedwires。工作线圈使用这种技术通常包括只有少数变成一个thickcopper大电流的导体,但许多数百或数千ampsflowing。(这是必要得到所需的安匝做对入门加热。)水的冷却是常见的,但是ofsystems最小。这是需要删除多余的热量通过thelarge产生的高频电流通过工作线圈及其相关的tankcapacitor
在parallelresonant储能电路工作线圈可以被认为是一个很感性负载功率因数校正”电容器连接在它。这个PFCcapacitor提供无功电流流大小相等、方向相反的电流largeinductive著作的吸引线圈。要记住的关键一点是那种巨大的电流是本地化工作线圈和电容器,merelyrepresents无功功率冲激两者之间来回。Thereforethe唯一真正的电流从逆变器是相对小的损失amountrequired克服“PFC“电容器和工作线圈。总是有一些损失在这个柜电路由于介电损耗在thecapacitor和趋肤效应导致电阻电容和workcoil损失。因此一个小电流总是来自逆变器即使noworkpiece礼物。当一个损耗件插入到工作线圈,thisdamps并联谐振电路的引入进一步损失到该系统。因此当前制定由平行谐振槽circuitincreases当工件进入线圈。
阻抗matchingOr只是“匹配”。这指的是电子产品,sitsbetween源高频功率和工作线圈我们使用forheating。以热一块实心的金属通过感应加热我们需要引起巨大的电流流表面的金属。然而thiscan对比与逆变器产生的高频功率。变频器一般作品更好的(和设计显得容易些)如果itoperates在相当高的电压,但一个低电流。(通常是问题在电力电子areencountered当我们试图开关大电流在很短的时期andoff上。)增加电压和减少currentallows常见的开关模式场效电晶体(或快速IGBTs)使用。这个comparativelylow电流使逆变器没有那么敏感,strayinductance布局问题。它的工作匹配网络和工作线圈本身对于高压/低电流逆变器的thelow-voltage /大电流加热工件所需有效。我们可以把坦克电路合并工作线圈(Lw)及其电容器(连续波)作为一个并联谐振电路。这有一个电阻(R)由于损耗件工作coildue耦合的两个导体之间的磁耦合。看到对面的示意图。在实践工作线圈的电阻,电阻的tankcapacitor,反射的电阻的工件都引入一个lossinto坦克电路和抑制共振。因此它是有用的combineall这些损失成一个单一的“损耗电阻。“对于aparallel谐振电路这损耗电阻直接出现在我们的模型tankcircuit对面。这个电阻代表唯一的组件,可以消耗传统实权,因此我们可以认为这个损耗电阻作为theload,我们正试图驱动功率在一个有效的方式。
当驱动atresonance当前绘制的坦克电容和工作线圈是equalin级和反相的,因此彼此抵消作为动力之源faras而言。这意味着只有负载被力量源在共振频率是在tankcircuit损耗电阻。(注意,当驱动两侧的共振频率,产生了一个额外的“相”组件当前byincomplete造成取消工作线圈电流和坦克capacitorcurrent。这种无功电流增加总级的电流beingdrawn从源但并不导致任何有用theworkpiece加热。)匹配网络的工作就是改变这个相对largeloss电阻在振荡回路推到一个较低的价值,更好的suitsthe逆变器试图驱动它。有许多不同的方式来achievethis阻抗变换包括攻丝工作线圈,使用ferritetransformer、电容分压器代替坦克电容器,或matchingcircuit如l匹配网络。对于一个l匹配网络它可以改变相对较高的loadresistance储能电路到10欧姆左右,bettersuits变频器。这个图是典型的允许逆变器运行fromseveral几百伏而保持电流降到一个中等水平所以thatstandard开关模式场效电晶体可以用于执行切换操作。网络包含的l匹配组件和Cm显示相反的,是不是
networkhas的l匹配几个非常可取的属性在这个应用程序中。在输入电感l匹配网络提出了一个逐步上升的inductivereactance所有频率高于谐振频率的tankcircuit。这是非常重要的,当工作线圈是美联储从avoltage-source逆变器,生成一个squarewave电压输出。这是anexplanation为什么是这样的…squarewave所产生的电压和论文之全桥式半circuitsis最丰富的高频谐波以及想要fundamentalfrequency。直接连接的这样一个电压源和一个平行resonantcircuit会导致过度的谐波电流流在所有的drivefrequency !这是因为坦克电容的并联谐振circuitwould呈现出逐渐降低increasingfrequencies容抗来。这可能是非常损害一个电压型三电平逆变器。Itresults在大电流峰值在开关转换为invertertries快速充放电电容器的坦克和fallingedges squarewave上升的。将l匹配网络和储能电路之间theinverter否定这个问题。现在输出的theinverter看到感抗的Lm在匹配网络第一,所有的谐波驱动波形看到一个逐渐上升的电感阻抗。这意味着最大电流流在预定频率只有和littleharmonic电流流动,使逆变器负载电流成
最后,correcttuning l匹配的网络能够提供一个轻微的电感负载到theinverter。这稍微滞后逆变器负载电流可以facilitateZero-Voltage-Switching(ZVS)的场效应管在逆变桥。Thissignificantly减少开机开关损失由于设备输出capacitancein mosfet在高电压下操作。总的结果是少thesemiconductors加热,增加寿命。总之,包含一个l匹配网络的逆变器和theparallel之间的谐振回路电路达到两件事。阻抗匹配,这样所需数量的电力供应从逆变器到工件,陈述的崛起的感抗,高频谐波变频器保持安全与快乐。看着前面的原理图我们可以看到,电容器在thematching网络(Cm)和坦克电容器(连续波)都是在平行。在现实世界中这两种函数通常是由一个purposebuilt完成电力电容器。它的大部分电容可以看成是inparallel共振与工作线圈,少量提供theimpedance匹配动作与匹配电感器(Lm)。这些twocapacitances梳理成一个引领我们到达工作coilarrangement LCLR模型,一种常用的行业为感应加热。
工作安排的LCLR coilThis包含工作卷成一个并联谐振circuitand使用l匹配网络之间的储能电路和逆变器。Thematching网络是用来使储能电路显示为一个更suitableload到逆变器,其推导了上面的部分。这个LCLR工作线圈有很多可取的属性:一个巨大的电流在工作线圈,但逆变器只有提供向下电流。大型循环电流是仅限于工作线圈和itsparallel电容器,它通常位于非常接近对方。只有相对较低电流沿传输线从theinverter到储能电路,所以这可以使用更轻的责任电缆。任何杂散电感的输电线路简单地成为matchingnetwork电感(Lm)。因此热站可以位于从逆变器了。看到一个正弦变频器负载电流所以它可以受益于ZCS或ZVSto减少开关损耗,因此,运行冷却器。该系列匹配电感可以被改变来迎合不同的负载placedinside工作线圈。坦克电路可以通过几个匹配电感美联储从许多invertersto达到功率水平高于与单个逆变器实现的。Thematching电感提供固有共享的负载电流theinverters之间,同时使系统宽容一些失配在theswitching瞬间的逆变器并联。为更多的信息的行为LCLR谐振网络看到新章节标记“LCLR网络频率响应。“LCLR的另一个优点是,它工作线圈安排不requirea高频变压器提供阻抗匹配函数。铁氧体变压器能够处理几千瓦是大型、重型andquite昂贵。此外,变压器必须冷却到removeexcess所产生的热量的高电流的导体。Theincorporation的l匹配网络的LCLR工作线圈arrangementremoves变压器的必要性以匹配逆变器工作线圈,节约成本,简化了设计。然而,设计师应该appreciatethat 1:1隔离变压器还需要在逆变器和输入LCLR工作线圈安排如果电气隔离isnecessary从电源供应。这取决于隔离是重要的,主要的事业单位是否在感应加热器已经提供了sufficientelectrical隔离来满足这些安全要求。
概念schematicThe系统示意图下部显示了最简单的变频驱动其LCLR workcoil安排。注意,这个原理并不显示MOSFET的栅极驱动电路andcontrol电子!在这个演示样机的逆变器是一个简单的两MTW14N50 half-bridgeconsisting mosfet使我在半导体(formerlyMotorola。)这是美联储从一个平滑的直流供电与去耦电容器的rails支持交流电流要求的逆变器。然而,它应该认识到,质量和调节电源inductionheating应用程序并不是关键。全波整流(但联合国平滑)电源可以工作以及平滑和直流稳压heatingmetal时,但峰值电流是较高的相同的平均加热功率。有很多参数的大小保持直流母线电容器降到最低。特别是它提高了功率因数的电流供应来自themains通过整流器,它也最小化存储能量,以防offault条件在逆变器。这个直流阻断电容仅仅被用来阻止直流输出half-bridgeinverter造成电流通过工作线圈。这是sizedsufficiently大,它不参与阻抗匹配、死了,没有不良影响的操作LCLR工作线圈的安排。
在高功率designsit是共同使用一个论文之全桥式(定速)4或更多的开关设备。书的设计匹配电感通常平均分担twobridge之间的双腿,以便驱动电压波形与尊重toground是平衡的。这个直流阻断电容也可以消除如果当前modecontrol是用来确保没有净直流流桥腿之间。(Ifboth腿定速的可独立控制还有scopefor控制功率吞吐量使用移相控制。看到点6在下面这部分关于“功率控制方法”获得更多细节)。在更高权力可以使用几个独立的inverterseffectively并联在一起,以满足高负荷电流的要求。然而,独立逆变器没有直接关系的outputterminals并行的h桥。每个分布式逆变器连接到远程工作线圈通过自己的一双匹配电感器,以确保总负载均分所有的逆变器。这些匹配电感还提供许多额外的好处wheninverters以这种方式是平行的。首先,任何twoinverter输出之间的阻抗等于两次匹配电感的值。Thisinductive阻抗限制“射之间“当前,flowsbetween逆变器并联,如果他们不perfectlysynchronised切换瞬间。其次,这个相同的感应电阻率之间limitsthe逆变器故障电流上升如果逆变器的一个展览,从而完全消除了devicefailure失败进一步设备。最后,因为alldistributed逆变器已经连接通过电感器,逆变器之间的任何additionalinductance仅仅增加了这种阻抗和只有略微的降解效果目前共享。因此,对感应加热distributedinverters不一定坐落physicallyclose对方。如果隔离变压器是包含在设计然后他们甚至不需要运行从相同的供应!
故障toleranceThe LCLR工作线圈布置很好表现在各种各样的possiblefault条件。打开电路工作线圈。短路工作线圈,(或槽电容器。)在工作线圈短路转。开路罐电容器。所有这些失败导致增加阻抗被呈现到逆变器,因此相应的下降来自theinverter当前。作者亲自用螺丝刀短路betweenturns的工作线圈携带几百安培。尽管火花飞溅在位置的应用短路、负载的逆变器是系统的reducedand轻松度过这待遇。最糟糕的事情是,储能电路变得显著提升其自然共振频率失谐就在上面操作频率是逆变器。自驱动频率仍接近共振那里依然重要的电流的逆变器。但根据功率因数由于失谐,逆变器负载电流开始thevoltage铅。这种情况是不可取的,因为负载电流被theinverter变化方向施加电压变化之前。结果是,目前这是力整流二极管和场效应晶体管之间靠惯性滑行theopposing每次MOSFET是打开的。这导致了一forcedreverse复苏的随心所欲行事二极管同时他们已经carryingsignificant正向电流。这个结果在一个大电流冲击通过boththe二极管和对立,是打开MOSFET。而不是一个问题对于特殊快恢复二极管,这迫使recoverycan导致问题如果场效电晶体固有体二极管用于提供thefree-wheel二极管函数。这些大电流峰值功率损耗和仍然是乳癌的威胁可靠性。然而,它应该berealised,适当控制逆变器的工作频率应该保证它跟踪谐振频率的振荡回路。因此theleading功率因数条件应该不起来,应该certainlynot持续一段时间。谐振频率应该被跟踪到它的极限,然后系统关闭如果它已经在外边闲逛的容忍的频率范围。
功率控制methodsIt常常希望控制能量的量inductionheater中处理的。这决定了速度,热能转移到theworkpiece。这种类型的权力设置的感应加热器可以controlledin许多不同的方法: 1． 改变直流环节电压。逆变器的功率处理均可降低supplyvoltage到逆变器。这可以通过运行逆变器从avariable电压直流供应如可控整流器使用晶体闸流管的直流电源电压tovary来自交流电源。对逆变器的impedancepresented基本上是常数在不同功率水平,所以力量吞吐量的逆变器大致成正比的平方的供应电压。改变直流环节电压允许完全控制powerfrom 0�0到100�t应该注意但是,准确的功率吞吐量在kilowattsdepends不仅在直流供电电压的逆变器,但也在loadimpedence工作线圈礼物到逆变器通过matchingnetwork。因此如果精确功率控制是必需的实际inductionheating功率必须测量,而要求“powersetting”操作符和一个误差信号反馈给continuallyadjust直流环节的电压在一个闭环方式错误降到最低。这是需要保持恒功率的workpiecechanges因为阻力大大因为它升温。(这个理由闭环powercontrol也适用于所有的方法,遵循下面。)
2。不同的dutyratio中的设备的逆变器。逆变器的功率处理均可降低准时在交换机逆变器。权力只有采购工作线圈在时间,设备开启。负载电流是通过设备就离开tofreewheel身体二极管在空载时间当两devicesare关掉。改变占空比的开关允许完全控制在权力从0 0到100��20然而,该方法的一个明显的缺点是重电流整流设备和他们的free-wheeldiodes之间活跃。迫使反向恢复的二极管,可以发生随心所欲行事当占空比是大大减少。因为这个原因占空比控制不是通常用于大功率感应加热逆变器3。不同的操作频率的逆变器。这个电源供给逆变器工作线圈可以减少detuningthe逆变器从自然共振频率的坦克circuitincorporating工作线圈。随着工作频率的逆变器ismoved远离共振frquency的储能电路,有lessresonant增加储能电路,电流在工作线圈减少。因此少循环电流感应到工件和向效果下降。为了降低功率吞吐量的逆变器通常是在一侧的失谐高柜电路自然共振频率。这导致theinductive电抗在输入匹配电路成为increasinglydominant随着频率增加。因此当前theinverter来自由匹配网络开始相位滞后和减少inamplitude。这些因素都有助于减少在现实powerthroughput。除了这些滞后功率因数确保thedevices在逆变器仍然打开与零电压,有不随心所欲行事二极管恢复问题。(这可以与形势,将发生如果逆变器是失谐偏低的线圈的谐振频率的工作组。ZVS丢失,随心所欲行事二极管反向恢复seeforced同时载有重要的负载电流)。
该方法通过控制功率水平失调是非常简单的,因为大多数感应heatersalready控制操作的频率逆变器为了tocater不同工件和工作线圈。缺点是它onlyprovides有限范围的控制,因为是有限度的powersemiconductors多快可以开关。尤其是在高powerapplications设备可能已经接近maximumswitching速度。高功率系统使用该功率控制方法需要基于深思热分析的结果,在不同的powerlevels切换损失,确保设备的温度始终保持在可承受的范围。对于更详细的信息关于功率控制由解谐看到下面newsection贴上“LCLR网络频率响应”。4。电感的值不同的匹配网络。这个电源供给逆变器工作线圈可以因正在改变整个价值的匹配网络组件。网络之间的l匹配inverterand坦克电路技术包含一个电感和一个capacitivepart。但电容部分是与工作线圈的tankcapacitor,实际上这些通常是一个和相同的部分。Thereforethe只是部分匹配网络,可用来调整是theinductor。匹配网络是负责把负载阻抗的theworkcoil到合适的负载阻抗是由逆变器。正在改变整个电感匹配电感器调整值loadimpedance是翻译。一般来说,减小电感的matchinginductor导致工作线圈阻抗要转换到一个lowerimpedance。这个较低的负载阻抗被呈现给逆变器causesmore权力是来源于逆变器。相反,增加theinductance匹配电感会导致更高的负载阻抗,bepresented到逆变器。这轻负荷导致更低的功率流从逆变器工作线圈。功率控制的程度成为可能通过改变匹配电感ismoderate。还有一个转变的共振频率的overallsystem——这是必须付出的代价结合l匹配电容andtank电容组成一个单元。网络的l匹配实质上是借一些电容从水槽电容器执行匹配操作,thusleaving坦克电路产生共振,更高的频率。因为这个原因thematching电感器通常是固定或调整粗步骤适合theintended工件被加热,而不是提供用户一个fullyadjustable电源设置。
5。阻抗matchingtransformer。这个电源供给逆变器工作线圈可以个别coarsesteps通过使用一个抽头的射频功率变压器进行阻抗变换。虽然大多数的利益LCLR安排在消除abulky和昂贵的铁氧体电力变压器,它可以满足大型系统参数变化的方式是不会频率依赖性。这个ferritepower变压器也可以提供电气隔离以及performingimpedance转换任务设置功率吞吐量。另外如果铁氧体电力变压器的逆变器之间放置产出带来帮助和输入电路设计的l匹配约束是悠然自得很多方面。首先,定位在这个位置的变压器意味着theimpedances两绕组相对较高。即电压高和currentsare comparitively小。它是容易设计传统的铁氧体powertransformer对于这些条件。大规模的循环电流在workcoil保存的铁氧体变压器大大减少冷却问题。其次,尽管变压器将方波输出电压从theinverter,绕组电流是正弦曲线的携带。缺乏高频谐波减少加热在变压器由于集肤效应andproximity效应在导体。最后,变压器设计应该是专为最低inter-windingcapacitance和良好的绝缘牺牲增加漏电感。其原因是,任何漏电感由transformerlocated展出在这个位置也仅仅是增加了匹配电感在输入到l匹配电路。因此在变压器漏电感不asdamaging性能作为国米绕组电容。
6。Phase-shiftcontrol定速的。当工作线圈驱动电压美联储论文之全桥式(定速)inverterthere是另一种方法实现功率控制。如果switchinginstants两桥臂的可独立控制的可能性,然后打开对话的控制功率吞吐量通过调整阶段shiftbetween两桥臂。当两桥臂开关到底在阶段,他们都samevoltage输出。这意味着没有电压工作线圈安排和有关工作线圈流过。相反,当两个桥臂switchin反相最大电流流经工作线圈和最大heatingis实现。功率水平介于0和100��0 0可以通过不同thephase转变的驱动到一个一半的桥梁0度和180年相比,degreeswhen驱动其他桥腿。这种技术是高度有效的功率控制可以实现在低收入功率控制侧。功率因数被逆变器总是remainsgood由于逆变器不是从共振频率的失谐的工作组线圈,因此无功电流流过二极管isminimised随心所欲。感应加热CapacitorsThe要求电容器用于大功率感应加热areperhaps最苛刻的任何类型的电容器。银行使用的电容器在振荡回路的感应加热器必须携带完整的电流,flowsin工作线圈长时间。这是典型的有上百安培的电流在数十或数百千赫。他们也exposedto重复100�0电压反转在同样的频率和看到fullvoltage发达整个工作线圈。高工作频率causessignificant损失由于介电加热,由于趋肤效应在theconductors。最后杂散电感必须保持绝对的最小以便电容器出现作为一个集总电路元件thereasonably相比低电感的工作线圈连接。
正确的选择ofdielectrics和扩展箔施工技术是用来减少很大的热生成和保持有效串联电感最小。然而,即使有这些技术感应加热电容器仍然exhibitsignificant功耗由于巨大的射频电流必须携带。因此在他们的设计的一个重要因素是允许有效的removalof热内的电容器来延长其寿命介质。下面的制造商生产的目的建立组件:高能源公司(英国分配器是AMS技术。)威世组件。Celem电力电容器。总部设在以色列。范围的大功率感应加热电容器从高能源集团高功率传导冷却的云母电容器从Celem电力电容器。Celem(图片由史蒂夫·康纳)注意大表面积的连接板的Celemconduction-cooled组件和无功功率等级(千乏)印刷在评级标签。更高的功率单位上图在铝情况下对水haveconnections冷却水管内部移除所产生的热量。
LCLR networkfrequency responseThe LCLR网络是一种三阶谐振系统由两个电感,一个电容和一个电阻。下面的波德图显示了这些方法在网络中电压和电流的变化,驱动frequencyis改变。绿色的痕迹代表当前通过matchinginductor,因此负载电流被逆变器。红色的tracesrepresent整个柜电容的电压,这是thevoltage一样在感应加热工作线圈。ACmagnitudes顶部图显示了这两个量,同时底部图显示了relativephase的信号相对于交流输出电压的逆变器。从振幅部分的波德图可以看出,整个工作的最大电压富饶线圈(顶部红色痕迹)在一个频率只有。在thisfrequency电流通过工作线圈也最大,最大的heatingeffect是发达在这个频率。可以看出,这frequencycorresponds最大负载电流来自逆变器(顶部绿色痕迹。)值得注意的是,巨大的逆变器负载电流有一个nullat频率仅略低于使最大加热。Thisplot显示精度的重要性在一个感应heatingapplication调优。对于一个高Q系统这两个频率非常接近。最高功率之间的区别和最小功率可以只有一个fewkilohertz。从底部图我们可以看到,对于频率低于最大powerpoint,工作线圈电压(绿色)是同相的输出电压从逆变器。随着工作频率增加了workcoil电压相角的变化突然通过180度(逆相)对最大功率点,在被加工。这个阶段的角度workcoil电压然后仍然旋转了180度从逆变器outputvoltage对于所有频率高于最大功率点。
从底部graphwe还可以看到,从逆变器的负载电流展品不是一个而是twoabrupt相位变化的操作频率是逐渐增加的。逆变器负载电流滞后于逆变器的最初输出电压90度在低频段。负载电流突然也通过180度相位超前的去往90度随着工作频率通过“零频率”的网络。逆变器电流仍然领先by90度直到达到最大功率点,再通过180度abruptlyslews并返回到90度滞后阶段再次。当我们考虑,只有电流的逆变器输出电压同相,与导致真正的权力转移,我们可以看到,theseabrupt转换从-90度到90度显然需要一个更detailedexamination……上面的波德图显示了兴趣的区域在零频率和最大功率点更多的细节。它还显示了一个家庭的行为curvesdepicting感应加热储能电路各种不同工件的礼物。这允许我们去感受一下该networkbehaves大损耗工件,工件没有出席所有,所有负载之间。没有工件安装,损失是低和Q值高。这givesrise急剧的峰值电流和电压在顶部的图,和theabruptly改变相移在底部图。作为一个有损耗的工件isintroduced整体品质因数的LCLR网络瀑布。这导致lessresonant增加逆变器负载电流和电压workcoil对面。共振峰变得不那么高,和更广泛的品质因数下降。同样的相位逆变器电流波形和工作线圈voltageslew迅速降低问因素少。
从这些图表我们candeduce几个影响任何控制系统,必须跟踪resonantfrequency LCLR的安排和控制功率吞吐量。首先产生了更多的共振提高LCLR网络当没有工件礼物。因此当前交付从逆变器应降低预防工作线圈和坦克电容电流等值的任何重大损失的带不带系统。其次,逆变器负载电流不存在流体载荷必须跟踪非常准确如果逆变器并不是看到要么领导或滞后负载电流,因为它也通过zerodegrees如此迅速。相反,我们可以说,有一个很大的损耗件礼物,就声称这次逮捕共振固有的崛起LCLR安排和逆变器将不得不提供更多的负载电流以达到所需水平的currentin工作线圈。然而,控制电子产品现在不需要跟踪theresonant频率如此密切自减弱问给负载电流thatshifts阶段更悠闲的态度。最后一个点的数量是值得考虑的一个自动控制whenconsidering阴谋以上战略跟踪谐振频率的一LCLR感应加热器。对于非常有损工件材料,(或大型volumesof金属,引入一个重要的总体损失)我们可以看到,theinverter负载电流相位(底绿色情节)有时未能曾经crossthrough零摄氏度的主要阶段。这意味着逆变器负载currentwith沉重的工作量不能同步和总是滞后一些金额。此外,逆变器负载电流不单调频率扫。因此直接反馈从电流互感器(CT)在inverteroutput不是一个可行的选择。虽然它可能似乎工作好与noworkpiece安装或只有温和的热负荷,它没有跟踪resonantfrequency正确和将无法操作满意作为workloadincreases和网络问瀑布!(直接从逆变器输出反馈currentusing CT形成一个自由运转的功率振荡器产生一个设计whichoscillates在低负载但掉出来的自激振荡工作负载时isincreased。)相比之下我们可以看到工作线圈电压(和坦克电容电压)阶段(底红图)是单调增加的频率。此外itconsistently经过-90度相位滞后点到底在频率使最大功率无论如何工作线圈isloaded严重。这两个优点使坦克电容电压波形一个excellentcontrol变量。总之变频器频率应控制soa实现一致的90度间隔柜电容电压和逆变器输出电压以达到最大功率的吞吐量。我们现在标签一些地区的兴趣在波德图下面。白色的垂直线表示频率的坦克capacitorvoltage(还有工作线圈电压)滞后于逆变器输出电压90度。这也是点了最大电压和最大电流在线圈的工作组流经它。白色的线是你想要开发的最大可能加热效应在工件。如果welook在逆变器负载电流相位(底绿色情节)我们可以看到那种总是0度至-90度之间当它穿过了白色它们分别为lineno怎么突然或慢慢地它也。这意味着一个负载电流的逆变器alwayssees,要么是同相或在最坏的inpower略滞后因素。这种情况是理想的支持ZVS软切换在逆变器和防止随心所欲行事二极管反向恢复问题。看右边的白线我们有面积阴影在蓝色标记“感应负载区域。“随着工作频率是increasedabove最大功率点的电压,工作线圈减少少热效应产生的工件。这个逆变器负载currentalso瀑布和开始相位滞后相对于输出电压的theinverter。这些特性使蓝色阴影区域的理想场所tooperate为了达到控制感应加热功率。通过detuningthe逆变器驱动频率在高端的最大功率点,powerthroughput是可以减少的,逆变器总是看到一个滞后功率因数。
相反地,左的白线我们有一个频率带标记“CapacitiveLoad地区。“随着工作频率降低maximumpower下面点,工作线圈电压也下降,少takesplace热效应。然而,这是伴随着逆变器负载电流possiblyslewing知名相角当损失在工件很低,Qfactor高。这是不受欢迎的许多固态逆变器作为theleading负载电流引起损失的ZVS和导致强迫offree-wheeling二极管反向恢复引起的开关损耗和电压超调量提高。因此,电容性负载区域是不推荐用于实现powerthroughput控制。垂直的紫色线标志着另一端的电容性负载区域,那里的逆变器负载电流转换再落后”归纳“负载电流。这是littleinterest第二感应区域,因为它没有达到显著的功率吞吐量,并不能bereached没有通过潜在的破坏性regionanyway电容性负载。当LCLR网络从squarewave驱动逆变器voltagethere也面临巨大的电流在一个谐波的drivefrequency。它被标记在图在这里仅仅是为了完整性。
注意:这个阶段是坦克电容电压被认为是一个控制变量和discussedextensively上面的情节。这是因为这个电压可以easilysensed使用高频电压互感器和提供所有必要的控制信息。同时它具有90度相位shiftrelative到逆变器输出电压(可能首先出现不良),它仍然是一个更好的控制变量要比坦克capacitorcurrent感。虽然坦克电容电流同相的电流可以inverteroutput这几百安培使闭合铁心铁素体CTsimpractical。此外90度相位偏移的坦克capacitorvoltage波形意味着它的零交叉故意流离失所的亲密的远离潜在的嘈杂的开关瞬间的逆变器。这- 90度移相的电压反馈信号可以被允许在设计的控制电子和是一个小的代价,easedsensing和增加免疫力的噪音了。
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波形 这表明theinverter输出电流波形当驱动LCLR工作线圈arrangementclose其共振频率。这个点对应于最大powerthroughput,因此最大加热效应。注意如何在逆变器loadcurrent几乎是一个纯粹的正弦曲线。这显示了逆变器输出电流波形的LCLR开车时工作coilarrangement大大高于其自然共振频率。这operatingpoint给降低功率吞吐量和降低热效应。Atfrequencies高于自然共振频率的工作coilarrangement LCLR的感抗的主导和theinverter匹配网络的负载电流滞后于应用的电压。注意到三角loadcurrent感性负载引起的squarewavevoltage结合逆变器输出。这显示了电压工作线圈在正常操作时,drivenclose共振。注意,电压波形是一个纯正弦曲线inshape。这也适用于当前波形和最小化harmonicradiation和射频干扰。在这种情况下的电压,工作线圈也高于直流总线电压提供给逆变器。这两theseproperties出自高q值因素的感应加热储能电路。 他显示了outputvoltage从逆变器当它是一个频率,数目低于谐振频率的原始工作线圈。注意到非常快的上升和falltimes squarewave伴随着过度电压超调、振铃。这些都归功于迫使反向恢复的MOSFET的身体diodeswhilst持久这不良的操作模式。(过度和振铃是dueto反向恢复电流峰值冲击激动人心的杂散电感在theinverter布局成寄生振荡)。这显示了输出电压的逆变器当它是调谐非常slightlyabove自然共振频率的工作线圈。注意,andfall崛起时代的squarewave更可控,有comparativelylittle过头或振铃。这是由于零电压开关(ZVS)举行当变频器运行在这个有利的操作模式。这显示了逆变器输出电压的精确调整时对谐振频率的工作线圈。虽然这种情况actuallyachieves最高功率吞吐量,并不完全实现零VoltageSwitching的mosfet。注意小等级的上升,fallingedges电压波形。这些发生的原因的中点bridgeleg尚未完全转换到相对供应铁路在thedead-time MOSFET在下次打开。在实践中少量ofinductive电抗呈现给逆变器帮助提供requiredcommutating电流,实现ZVS。因为这个原因情况describedfor前面的照片比被精确一致。
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