Adaptive reference voltage generator for firing angle control of

Abstract

A control system for a permanent-magnet motor (10) driven by a multiphase line-commutated inverter (12) is provided with integrators (24) for integrating the back EMF of each phase of the motor for use in generating system control signals for an inverter gate logic (30) using a sync and firing angle (.alpha.) control generator (26) connected to the outputs of the integrators. A precision full-wave rectifier (16) provides a speed control feedback signal to a phase-delay rectifier (14) via a gain and loop compensation circuit (20) and to the integrators for adaptive control of the attenuation of low frequencies by the integrators as a function of motor speed, whereby as the motor speed increases, the attenuation of low frequency components by the integrators is increased to offset the gain of the integrators to spurious low frequencies. The .alpha.-control signals are produced by the firing angle control generator by means (48, 50) for combining 120.degree. segments of the integrated back EMF signals symmetrical about their maxima into composite positive and negative waveforms, and means (45, 46) for sampling the maxima of each waveform every 120.degree.. These samples are then used as positive and negative .alpha.-control signals, whereby any change in amplitude of the integrated back EMF signals will not affect a change in the operating power factor of said motor and inverter.