Evaluation of the Output Voltage Harmonics of Typical PWM Methods in a Dual-inverter Fed Open-End Winding Induction Motor with a Floating-capacitor

This study aims to reduce the voltage harmonics caused by the pulse-width modulation (PWM) in a dual-inverter with a floating-capacitor (FC) topology in a partial-load condition. The system has more degrees of freedom, such as modulation indices (MIs) and phase angle difference, than the single-inverter system. This paper provides an analysis strategy for the output voltage harmonics when using various carrier-based PWM (e.g. sinusoidal-PWM (SPWM), third-harmonic-injection-PWM (THIPWM), discontinuous-PWM (DPWM), and space-vector-PWM (SVPWM)). The validity of the analysis was confirmed by simulations and experiments using an open-end winding induction motor (OEWIM). The voltage THD is reduced by maximizing MI of both inverters; experimental results show that the DPWM reduced the voltage THD from 1.29 to 1.18 and 2.06 to 1.89 at 0.50 p.u. and 0.25 p.u. of the rated-voltage compared with using SPWM, respectively. The waveform evaluation and the modulation method can contribute to waveform improvement and high-efficiency operation in the partial-load.