Experimental Study Based Switching Sequence for Reduction of Peak Voltage Transients in GaN-based 3L-ANPC Inverter

The high dv/dt and di/dt operation of GaN HEMTs lead to high turn-on and turn-off transient voltage overshoot (TOV). In a 3L-ANPC topology with redundant states of operation, the severity of transients also depends on the switching sequence. Multiple critical power commutation loops in a 3L-ANPC topology make the power loop design optimization a challenging task. Therefore, in cases where further design optimization is not possible, effective use of the different possible switching sequences can achieve lower peak voltage transients. Various possible switching sequences are compared in this work based on the severity of TOV. A modified full-mode formed by an additional high-frequency operation of the clamping switch is presented as an overvoltage mitigation strategy at high voltage and high current. A turn-on and turn-off transient severity analysis is shown for all considered switching modes based on an experimental three-level double pulse test. The test results present a GaN HEMT-equipped three-level ANPC phase leg operating at 700 V DC. Based on the analysis, a current-dependent switching sequence selection is presented to minimize the resulting peak voltage transients for continuous inverter operation.