A Low Switching Frequency SPWM Strategy for Open-winding Machine with Low Current Harmonics

In this paper, a novel sinusoidal pulse width modulation (SPWM) strategy with simple implementation is proposed for an open-winding machine fed by isolated DC-bus dual two-level three-phase inverters to reduce PWM switching frequency and current harmonics. A novel zero sequence voltage injection method is injected to the reference voltage of dual inverters in this strategy to reduce current harmonics and improve the voltage utilization of SPWM strategy. Moreover, an unbalance reference voltage distribution method is applied to generate different reference voltages for two inverters. In the proposed strategy, only three of six legs of dual inverters are switched in a PWM cycle, and thus the switching frequency is halved, while the current harmonic characteristic can be improved, compared with the conventional SPWM strategy. The superiority of the proposed SPWM strategy is validated by simulation and experiment results.