Patent ID: 8878480
Filing Date: 2014-11-04
Classification: H02P

Abstract:
1. A synchronous motor drive system comprising an inverter connected to a three-phase synchronous motor and comprised of a plurality of switching elements, and a controller for selecting two energized phases of the three-phase windings of said three-phase synchronous motor and controlling the energization of said inverter according to six different energizing modes by means of pulse-width modulation; wherein said controller comprising an energizing mode switching means for detecting at least either a terminal voltage of a de-energized phase of said three-phase windings or a connection point voltage of a stator winding of said three-phase synchronous motor and sequentially switching said energizing mode according to the detected voltage, and a rotation count computing means for retaining an instantaneous value one or more samples earlier of an instantaneous voltage which is detected on a predetermined sampling period, calculating a difference value between said voltage retained at the time when the sign of said detected voltage was inverted and a currently detected voltage, and calculating the number of rotations of said three-phase synchronous motor based on the difference value, in an area where the rotation speed of said three-phase synchronous motor is from zero through low speed.