Implementation of nondeterministic PWM for inverter drives

Abstract

A single-phase power factor pre-regulator to improve the power quality in the input side of the AC/DC/AC converter and a random PWM to reduce the emitted acoustic noise and the mechanical vibration for induction motor drive is presented in this paper. The hysteresis current control (HCC) technique for a voltage source PWM rectifier is adopted. A control scheme is presented that ensures that the line current is driven to follow the reference current which is derived from the DC bus voltage regulator and the output power estimator. A random pulse position technique for a three-phase PWM inverter system for an induction motor control to reduce the annoying tonal noise and resonant vibration from AC machine drive is described. By randomly varying the instantaneous pulse position from one cycle to the next, the frequency distribution of harmonics is spread in a wide frequency range. The major advantage for using such a strategy is nonrepetitive output spectral characteristics, which results in reduction of torque pulsations in motor drive systems. Experimental results show the nearly unity power factor at the PWM rectifier and the absence of acoustic noise concentrated at the specific tones which is usually present with conventional sinusoidal modulation.