Control Method for Reducing the Motor Loss of Dual-inverter Fed Open-end winding Induction Motor in the Low-speed Region

Abstract

This paper proposes a method for improving the output voltage waveform of dual-inverter fed open-end winding induction motors in the low-speed region. The system consists of two isolated DC power supplies, an open-end winding induction motor, and two voltage source inverters, which are connected to the opposite terminals of the open-end winding with unequal DC-link voltages. The motor losses, which are caused by the harmonics of the voltage applied to the winding, increase when the inverter outputs a pulse-width modulated voltage at a low modulation index. The aim of this paper is to reduce the motor loss at low motor speeds by improving the winding voltage waveform. In the proposed control method, the use of the output voltage difference from the inverters constituting the dual-inverter lowers the peak voltage. In order to obtain the proposed waveform, a method for the space-vector pulse-width modulation of the dual-inverter is presented. Furthermore, this paper presents the commutation sequence of the PWM pattern considering the dead-time and switching device characteristics, especially the turn-off delay time. The proposed method is verified experimentally by driving a dual-inverter fed open-end winding induction motor. The experimental results confirm that the harmonic component of the output voltage, which is related to the switching frequency (5kHz), is reduced from 18.9V to 4.4V by using the proposed method at a motor speed of 300rpm and load torque of 1.43Nm.