AC MOTOR ROTATION DIRECTION DETECTING METHOD AND ELECTRIC POWER CONVERSION DEVICE FOR AC MOTOR USING SAME

摘要

Provided is an AC motor rotation direction detecting method for rapidly and accurately detecting the rotation direction when the AC motor is restarted after the occurrence of an instantaneous power failure and also provided is an electric power conversion device. The electric power conversion device comprises: a power rectifier (21); a smoothing capacitor (22); an inverter (23) for converting the DC power output from the power rectifier to three-phase AC power with a desired frequency; and a control driving unit (4) for controlling the drives of switching elements constituting the inverter. In the rotation direction detecting method used in the electric power conversion device for the AC motor for supplying the AC power with the converted desired frequency to the AC motor, a timing (tA) or timing (tB) is detected, at which the AC voltages of the U-phase and V-phase of three-phase AC induced electromotive force from the AC motor are intersected with each other. When the three-phase AC power is supplied again to the AC motor after the output of the electric power conversion device is interrupted, some of the switching elements constituting the inverter are selectively driven responsive to the detected timing to form the flow path of a back-flow current between the inverter and the AC motor, thereby determining the rotation direction of the motor from the detected back-flow current.