Research on eliminating common-mode voltage of cascaded medium-voltage variable frequency driver with phase-difference SVPWM

For application to cascaded multi-level inverter, three phase-difference SVM (PD-SVM) schemes based on left and right bridge vectors are proposed firstly. For these three schemes, equivalent SPWM components are deduced, and unipolarity or bipolarity of output waveforms is analyzed. Use sampling time staggered SVM (STS-SVM) for reference, improved PD-SVM - STS PD-SVM can be applied to cascaded medium-voltage variable speed driver (MV-VSD). The mechanism of eliminating two sorts of CMV by one of improved PD-SVM schemes - STS 2pi/3 PD-SVM is analyzed in detail. Through the simulation results in the end, this modulation scheme can effectively eliminate CMV without reducing the utilization of the dc voltage excessively in contrast with conventional 3d-order harmonic injection SPWM.