MOSFET KILLER
New Member
Hello Everyone,
I have started this thread to post schematics, pictures, block diagrams and questions regarding my 10,000 watt induction heater project. I will outline most of the major components of the circuit and describe their function.
So, lets start with the power supply, I have a 240VAC, 60 Ampere line (14.4kVA). This is then passed through soft start resistors to charge the filter capacitors and prevent a massive current surge from tripping fail safes. Since a bridge rectifier distorts the current waveform I have included an active power factor correction circuit. I have chose to limit the output power by varying the DC inverter supply voltage. To do this I have placed a buck regulator on the ~400VDC output of my PFC pre-regulator. The buck regulator will give me control of the output power from 0 to 10,000 watts.
On to the frequency control circuitry, the two inputs are from a current transformer and the high side oscillator. They are compared by a type II phase detector and filtered by an RC network. As you can see it is essentially a phase locked loop that keeps the oscillator (a TL494) on the resonant frequency of the series resonant tank which can vary with loading. I also have control over the phase angle to keep the power factor low (as close to 1 as possible).
The IGBTs in my half bridge inverter are driven by a pair of identical IGBT drivers that consist of optically coupled TC4422 IGBT driver ICs, undervoltage lockout, and antisaturation detection circuits. Both the high and low side IGBT drivers are coupled to the oscillator with optocouplers for equal timing. The antisaturation detection circuits compare the IGBT collector voltage to a reference voltage and will give a high output if the collector and gate are both high at the same time.
My current detector provides feedback to the buck regulator to limit output power if the current becomes too high. This circuit will also trip an overcurrent latch if the current is high enough to indicate a fault.
I have also included safety interlocks since I am building a commercial model induction heater. They cover things such as cooling water and component temperatures.
The IGBT drivers drive a half bridge of IGBTs that turn the ~400VDC output of the power supply into high frequency AC (about 20 kHz). The inverter output supplies the primary of a ferrite transformer with a 10:1 turns ratio. The secondary is stepped down in voltage and isolated from the mains. The secondary supplies AC to a series resonant LC circuit, I opted to use series resonance after discussions with **broken link removed**. He told me that the capacitor in a parallel resonant circuit will periodically short circuit the inverter during switching, but in series switching is better.
I have covered most of the important components of this induction heater, questions, comments, suggestions are welcome.
Thank You,
Alex Sears
I have started this thread to post schematics, pictures, block diagrams and questions regarding my 10,000 watt induction heater project. I will outline most of the major components of the circuit and describe their function.
So, lets start with the power supply, I have a 240VAC, 60 Ampere line (14.4kVA). This is then passed through soft start resistors to charge the filter capacitors and prevent a massive current surge from tripping fail safes. Since a bridge rectifier distorts the current waveform I have included an active power factor correction circuit. I have chose to limit the output power by varying the DC inverter supply voltage. To do this I have placed a buck regulator on the ~400VDC output of my PFC pre-regulator. The buck regulator will give me control of the output power from 0 to 10,000 watts.
On to the frequency control circuitry, the two inputs are from a current transformer and the high side oscillator. They are compared by a type II phase detector and filtered by an RC network. As you can see it is essentially a phase locked loop that keeps the oscillator (a TL494) on the resonant frequency of the series resonant tank which can vary with loading. I also have control over the phase angle to keep the power factor low (as close to 1 as possible).
The IGBTs in my half bridge inverter are driven by a pair of identical IGBT drivers that consist of optically coupled TC4422 IGBT driver ICs, undervoltage lockout, and antisaturation detection circuits. Both the high and low side IGBT drivers are coupled to the oscillator with optocouplers for equal timing. The antisaturation detection circuits compare the IGBT collector voltage to a reference voltage and will give a high output if the collector and gate are both high at the same time.
My current detector provides feedback to the buck regulator to limit output power if the current becomes too high. This circuit will also trip an overcurrent latch if the current is high enough to indicate a fault.
I have also included safety interlocks since I am building a commercial model induction heater. They cover things such as cooling water and component temperatures.
The IGBT drivers drive a half bridge of IGBTs that turn the ~400VDC output of the power supply into high frequency AC (about 20 kHz). The inverter output supplies the primary of a ferrite transformer with a 10:1 turns ratio. The secondary is stepped down in voltage and isolated from the mains. The secondary supplies AC to a series resonant LC circuit, I opted to use series resonance after discussions with **broken link removed**. He told me that the capacitor in a parallel resonant circuit will periodically short circuit the inverter during switching, but in series switching is better.
I have covered most of the important components of this induction heater, questions, comments, suggestions are welcome.
Thank You,
Alex Sears
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