Low Torque Ripple Drive of Induction Motor by Multi-step PWM Inverter

Abstract

In this paper, we propose a novel multi-step PWM inverter useful for the torque ripple reduction of an induction motor. The PWM waveform can be easily obtained by exchanging alternately neighbour two voltage vectors among six output voltage vectors together with a zero voltage vector every 60 degree interval.
The basic principle and characteristics of the PWM inverter are shown at first. It is introduced that the harmonics C_n of the PWM voltage waveform approximately has the enough relation of _??_C_6m-1/(6m-1)=C_6m-1/(6m+1)_??_ to reduce the torque ripple of an induction motor by the cancellation of the 6m order power ripple components arising from the product of a fundamental component and 6m±1 harmonic components of the PWM waveform.
And then, the driving characteristics of an induction motor by the proposed PWM inverter are investigated from some simulation and experimental results comparing with the conventional PAM, rectangular PWM and sinusoidal PWM inverter.
The features of the PWM technique are high efficiency and low acoustic noise operations for the low torque ripple drive of an induction motor.
The PWM technique may be suitable for the induction motor drive using relatively slow and large switching power devices such as GTOs.