Implementation of nondeterministic pulse width modulation for three-phase inverters

This paper presents an AC/DC/AC converter with a power factor correction to improve the power quality in the AC mains and a pseudorandom noise generator to reduce the emitted acoustic noise for induction motor drive. The space vector modulation with hysteresis current regulator is adopted to simplify the control algorithm. The control scheme is proposed to force the line current in phase with the source voltage. The current reference for the pulse width modulated (PWM) rectifier is derived from the DC bus voltage regulator and the estimated output power. In order to reduce the annoying tonal noise and resonant vibration from the drive, random switching frequency technique for a three-phase induction motor control is described. By randomly varying the instantaneous PWM switching frequency from one cycle to the next, the frequency distribution of harmonics is spread in a wide frequency range. Experimental results show the nearly unity power factor at the PWM rectifier and the absence of acoustic noise concentrated at specific tones which is usually present with conventional sinusoidal modulation.