Synchronous Space Vector Voltage Modulation of Three-phase Inverter with Low Switching Number

For high-speed or high-power motor drive systems, it is difficult to use conventional pulse width modulation because of the high harmonic current. These harmonic currents are caused by the low-frequency beat phenomenon that occurs because the rotation flux and switching timing are not synchronized. In this paper, an N pulse synchronous voltage modulation method with low switching frequency is proposed based on variable time step control. Unlike the previous study, the variable time step current controller is analyzed in the z-domain and designed in a polar coordinate system. The plant model shows the cross-coupling effect between dq- currents. To solve this problem, the current decoupling controller is added to the feedback system. In order to obtain better harmonic characteristics, an N pulse synchronous space vector modulation method is also presented. The proposed method has better harmonic characteristics than the six-step operation in the region where the voltage modulation index is 0.85-1. The effectiveness of the proposed method is demonstrated by the simulation results.