Variable time step control for six-step operation in SMPMSM

Six-step operation has many advantages in Permanent Magnet Synchronous Machine (PMSM) drives such as extended utilization range of the inverter output voltage. However, the error in the voltage modulation can be occurred when the PMSM runs at ultra-high speed (above 50krpm), that is, the ratio of the sampling frequency to the fundamental frequency (F_ratio = f_samp/f_fund) is small. In this paper, the realization of the six-step operation in Surface Mounted PMSM (SMPMSM) with the variable time step control is proposed. The control variable is the time step in the proposed method. The torque is controlled by manipulating the time step. By updating the inverter output voltage on every time step, beat phenomenon caused by small F_ratio can be solved. The proportional and integral gains of the current controller are determined with consideration of the system stability. The feasibility of the proposed method has been verified by experiments.