DC-biased SPWM voltage control for six-phase switched reluctance motor drive based on N+2 power electronic converter

The converter of six-phase switched reluctance motor (SRM) requires both less switch devices and independence between phases. So instead of the frequently-used asymmetric half-bridge converter, N+2 power converter is employed in this paper. In N+2 power converter, SRM works in voltage chopping mode. While under common fixed duty-cycle PWM (FDPWM) voltage control, the torque ripple is high and the efficiency is low nearby the rated speed, during which the phase currents can hardly reach the chopped level and the angle position control of SRM is conducted. Besides, the torque sharing function (TSF) control is regarded as not suitable for this case. Therefore, in this paper a DC-biased SPWM (DSPWM) voltage control for SRM is proposed. The equivalent implemented voltage of each phase varies with rotor position according to the modulating wave of DSPWM. With parameters of DSPWM set appropriately, the active currents of each phase are lowered at the beginning and enhanced at the rest of conduction time. As a result, the efficiency of SRM will increase and the torque ripple will descend. Moreover, the DSPWM control can also help to lower the maximum current of switch devices and is easily realized. Finally, an 800W, 500 rpm, six-phase 24/20 SRM for electric bicycle is used as application objective and the simulation results are presented to verify the effectiveness of the proposed DSPWM voltage control.