VARIABLE-SPEED DRIVE FOR SINGLE-PHASE MOTORS

摘要

A single-phase variable-frequency power supply (1) with two output voltages (3, 4) drives a single-phase AC motor (6) that has a start circuit (7) and main winding (5). For permanent split-capacitor motors, the power supply (1) maintains a constant voltage to the start winding (7) while it reduces the voltage to the main winding (5) at lower frequencies. The power supply (1) can similarly control the speed of capacitor-start and split-phase motors. For fans and pumps and other variable-torque applications, the power supply (1) maintains approximately a constant ratio of main-winding voltage to the square of frequency. The power supply (1) is preferably an electronic pulse-width modulated inverter.