12kW PFC Boost Converter

  
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The project is a continuation of the 5kW Boost converter project. After a few failed attempts, I realized that I was really after more power, perhaps 10kW or so. I changed the title from 12kW to 8kW. While the converter is designed for 12kW, its very unlikely that I will ever run at that power level. So I expect the maximum output power to be 800V
12kW PFC Boost Converter - schematic

DC at 10ADC, so 8kW. Discontinuous current, power factor correcting boost converter. 2 converters are interleaved, each operating at 6kW maximum input power. There is an "active" snubber circuit that recycles snubber energy, this greatly reduces IGBT switching loss. Because the converter operates in a discontinuous mode, this implies 2 particular conditions. Firstly, the peak current will be about twice that of a continuous mode converter. Secondly, because the IGBTs don`t turn on with any current, we only care about the turn OFF losses, which will be quite high if not taken care of. The Turn OFF loss is caused by the instantaneous overlap of the IGBT voltage and current (in this case 850VDC and 100A). This overlap is very short, but can cause quite a bit of loss, which equates to hot IGBTs. The trick is to then place a capacitor across the IGBT so that the instantaneous voltage at shut off, is 0V, that is, until the capacitor gets charged. There is a diode in series with the capacitor, so that it could never discharge back through the IGBT when it turns ON. The problem then becomes: what to do with the energy in this capacitor A typical snubber places a resistor in parallel with this capacitor to drain off the charge. In this case, we are basically shifting the IGBT losses to power dissipated in this resistor. The nice thing is that we can locate said resistor remotely, but still, we have to get rid of that heat. My...



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