Analysis of turn-off behavior and switching losses of a 1200 V/50 A zero-voltage or zero-current switched IGBT

The authors describe the development of the basics for the determination of the maximum obtainable switching frequencies of a 20 kW, 820 V/50 V full-bridge DC-DC converter designed with (second-generation) 1200 V/50 A IGBTs (insulated-gate bipolar transistors). Because the turn-on losses can be almost completely avoided by phase-shift PWM (pulse-width modulation), emphasis is placed on the determination of the turn-off losses. The dependencies of the switching power losses per switching cycle on the load condition and on the junction temperature are investigated for the following cases: simple PWM (switching without snubber), switching with capacitive parallel branch (turn-off snubber network), and force commutation of the power electronic switches using a commutation circuit (zero-current switching). The results obtained indicate the possibility of rating the overall effort linked to a given operating mode of the power electronic devices. The limits of the operating region of the converter system can also be determined.<>