Reduction of Voltage Harmonics in an Open-End Winding Induction Motor Driven by a Dual-Inverter with Floating-Capacitor in the Low-Speed Region

A control method to reduce the voltage harmonics in an induction motor is proposed in this paper. This study aims to reduce the carrier harmonics, especially caused by the inverter switching in the low-speed region. The system consists of an open-end winding induction motor (OEWIM) and two voltage-source inverters (VSIs); the dual-inverter is powered by a single DC voltage source and has a capacitor bank. The motor losses, which are caused by the harmonics of the voltage applying to the winding, increase when the inverter outputs a pulse-width modulated (PWM) voltage at a low modulation index. In the proposed method, the use of the output voltage difference between the inverters constituting the dual-inverter lowers the harmonics by keeping the modulation index at high value in each inverter. The theoretical analysis indicates that when the OEWIM is driven at the low-speed condition in the case of using sinusoidal PWM, the voltage total harmonic distortion (THD) can be reduced compared with the single-inverter drive. The performance of the proposed method is simulated and experimentally verified. The results show that the voltage THD of the motor winding are reduced in the low-speed region by 13.9 % at a fundamental frequency of 10 Hz.