Variable-speed drive for single-phase motors

摘要

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