Alternating switching of inductive decoupled IGBTs in Voltage Source Inverters

A new switching scheme for ZVS of inductive decoupled high voltage IGBTs is proposed. Each half bridge, consisting of two IGBT and two diodes, is split into two parallel half-bridges. The outputs of these half-bridges are decoupled by an inductance. An alternating switching scheme leads to hard switching turn-off and zero voltage switching turn-on. The IGBT turn-on losses can be reduced to less than 10% compared to hard-switching. The reverse recovery stress for the free-wheeling diode determines the size of the decoupling inductor. As the IGBT turn-on and diode reverse-recovery losses are dominating at high voltage IGBT, the output current of the inverter can be significantly increased. In the paper, the different switching schemes for inductive decoupled inverter legs are compared. For the alternating switches scheme, the effect of the diode reverse recovery and the current redistribution during the conduction phases are explained in detail. Experimental results are given for 6.5 kV IGBT, the dependence of the diode reverse recovery stress on different operation parameters is discussed.