This paper demonstrates a unique voltage overshoot phenomenon of keep-off state devices in three level simplified neutral point clamped (3L-SNPC) inverter which comprises a DC-DC chopper and a three-phase two-level (2L) inverter. The issue is found to be related to the switching action of the DC-DC chopper and will introduce voltage overshoot on the constant keep-off state devices in the 2L-inverter. The switching transients of different switching cases are analyzed to reveal the mechanism of the voltage overshoot phenomenon. Based on the analysis, a snubber circuit is used to suppress the voltage overshoot. Simulations using LTspice software validate the analysis and the solution.
 

3L-SNPC, voltage overshoot, keep-off state devices, switching transients, snubber circuit