Patent ID: 6570778
Filing Date: 2003-05-27
Classification: H02P

Abstract:
An adjustable speed drive for single-phase induction motors having a main winding and an auxiliary winding comprising:(a) first and second input lines connectable to single-phase AC power lines; (b) a pair of DC bus lines; (c) a rectifier connected to the first and second input lines and to the DC bus lines: such that, AC voltage applied to the input lines is rectified to a DC voltage applied on the DC bus lines; (d) an inverter comprised of two gate controlled switching devices connected together across the DC bus lines; (e) a first output line connected to the first input line, a second output line connected to the second input line and a third output line connected to a node between the two gate controlled switching devices; and (f) a transfer switch circuit connected to the second and third output lines, and connected to a main winding supply line and an auxiliary winding supply line that may be connected to the main winding and auxiliary winding, respectively, of an induction motor, wherein the first output line may be connected to both the main winding and the auxiliary winding to complete the circuit therethrough, and a phase-shifting capacitor connected to the transfer switch circuit, the transfer switch circuit having switches switchable between a first position in which the second output line is connected directly to the main winding supply line and the third output line is connected to the auxiliary winding supply line and a second position in which the third output line is connected directly through the transfer switch circuit to the main winding supply line and is also connected by the transfer switch circuit through the phase-shifting capacitor to the auxiliary winding supply line.