Synchronous SVPWM over-modulation method based on zero-sequence voltage injection in locomotive traction

High speed motor control is a key technology in the locomotive traction system. Because of the limitation of the switching frequency and voltage level in high power inverter, modulation method with high voltage utilization ratio and lower low-frequency harmonics is necessary. In this paper, a novel PWM method equivalent with the traditional SVPWM method is proposed, which is realized by the comparison of zero-sequence voltage injected modulation wave and carrier-waves. The over-modulation and smooth transition to six-step square wave modulation was realized by the adjustment of the modulation wave. Moreover, the synchronous modulation can be applied to reduce low-frequency harmonics by the adjustment of the carrier-wave frequency. The corresponding motor control method including flux-weakening control and current open-loop control are also proposed in coordination with the modulation method. The validity of the proposed method has been verified by both simulation in MATLAB and experiments on an industrial 160kW, 750V experimental platform.