A Near-State PWM Method With Reduced Switching Losses and Reduced Common-Mode Voltage for Three-Phase Voltage Source Inverters

The near-state pulsewidth modulation (NSPWM) method, which reduces the common-mode voltage/current, is proposed for three-phase pulsewidth modulation (PWM) inverter drives. The method is described, its optimal voltage vectors are found, and the sequence that these vectors are applied is determined. Its voltage linearity and DC bus and AC output PWM current ripple characteristics are studied. Its output line-to-line voltage pattern is carefully studied with regard to switching transients that may cause overvoltages at the motor terminals, particularly for long-cable applications. The NSPWM method is thoroughly investigated, and its performance is compared to conventional PWM methods. Theory, simulations, and experiments show that NSPWM exhibits superior common-mode performance and satisfactory input/output PWM ripple performance characteristics. It is also illustrated that even though the method has bipolar line-to-line output voltage pulses, due to the sufficient zero-voltage time intervals for the switching transients to settle, these pulses do not cause additional overvoltages at the motor terminals compared to the conventional methods. The method is feasible for motor drives, particularly for operation in the high modulation index range, where its overall performance exceeds the performances of the state-of-the-art PWM methods.

I. Introduction

Three-Phase voltage-source inverters (VSIs) are widely utilized to drive ac motors with high motion control quality and energy efficiency, provide clean current waveform and regenerative operation in ac–dc power converter applications, and supply high-quality power in uninterruptible power supply ac–dc–ac power converter units. Pulsewidth modulation (PWM) is the standard approach in operating the inverter switches in order to generate the required output voltages. Conventional continuous PWM (CPWM) methods, such as space vector PWM (SVPWM), [1] and discontinuous PWM (DPWM) methods, such as DPWM1 [2], perform satisfactorily in terms of voltage linearity, output current ripple, dc bus current ripple, and average switching frequency requirements [3], [4]. However, they have poor common-mode voltage (CMV) and common-mode current (CMC) characteristics [5].