Variable switching frequency PWM strategy for inverter switching loss and system noise reduction in electric/hybrid vehicle motor drives

In order to reduce the inverter switching loss and system noise of electric vehicle (EV) and hybrid electric vehicle (HEV) motor drives operating in high output torque region, while preventing over-heating and demagnetization of the electric motor, this paper proposes variable switching frequency PWM (VSFPWM) strategies based on on-line prediction of current ripple RMS value for two typical motor drive systems of EV/HEV. First, the instantaneous output current ripple of three-phase inverter with SVPWM is analyzed in the time-domain. Then the current ripple prediction based VSFPWM strategies are proposed for both traction motor drive topologies to meet the current ripple RMS value requirement. Compared with constant switching frequency PWM (CSFPWM) method, the inverter switching loss and noise reduction capabilities of the proposed VSFPWM methods are analyzed. The effectiveness of the proposed methods is verified by both simulation and experiments.