Series connection of 3.3 kV IGBTs with active voltage balancing

Application of IGBTs (insulated gate bipolar transistors) to high voltage power electronics systems is today becoming an attractive solution because of low cost and low complexity. Semiconductor manufacturers are making efforts to design chips with higher blocking voltages, but for reliability and cost purposes, an easier solution today would be to use standard IGBTs. This paper describes the behaviour of 3.3 kV, 100 A chips connected in series and driven with an active gate control circuit which balances the voltage during both static and dynamic phase. The first part of the article presents the theoretical description of the principle and some design recommendations. The second part contains experimental results. These tests demonstrated that it is possible to safely turn off two times the nominal current under 4 kV DC link voltage. Finally, short-circuit turn-off has been also successfully tested, showing a good balancing of the overvoltages, even under such emergency conditions.