Patent ID: 6329785
Filing Date: 2001-12-11
Classification: H02P

Abstract:
A 4-step PWM switching controller for a variable speed induction motor having a stator and a rotor, the stator having main and auxiliary coils, comprising:a) four transistors arranged as two bidirectional switches, one switch controlling current to an inductive load and a second switch controlling a freewheeling path for inductive current when the first switch is not conducting;b) a power supply with only two isolated secondaries for receiving a single phase AC voltage and generating power for the controller;c) a digital controller having a PWM signal generator for accepting environmental demand signals dictating motor speed and generating PWM signals therefrom operative to create a duty cycle for the current path sufficient to bring the motor to the dictated speed;d) the digital controller further having commutation logic for switching the transistors in a set pattern with switching delays effective to allow use of the current path and the freewheeling path;e) two isolated gate drives for switching one of the bidirectional switches on and off in proper sequence;f) two non-isolated gate drives for switching the other of the bidirectional switches on and off in proper sequence; andg) the switches being connectable to at least some of the coils of the stator.