| 摘要 |
PURPOSE:To correct offset voltage, by retaining a current value in case that a motor keeps stopping for a fixed time or longer, and by subtracting the retained value from current feedback signal at the time of operation, to set the current value. CONSTITUTION:So far as a three-phase induction motor is concerned, a three- phase AC power source is converted to direct current by a converter, and by a PWM inverter, the direct current is turned into the AC output of variable voltage/variable frequency to drive the motor. A controller is composed of a coordinate converter circuit 15 to which the input of current feedback signals 12a-14a accommodated to the each-phase primary-current of the motor is provided, and the like. In this case, the coordinate converter circuit 15 is provided with current feedback signal retaining circuits 91A-91C and subtracters 92A-92C. Then, the control signal 93 of a retaining circuit 91 comes to a level H at fixed intervals at the time of stopping, and then, by the retaining circuit 91, the current feedback signal 12a-14a are respectively sampling-retained. As a result, their retaining values 95a-95c are to have no offset. |
