| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to perform a stable, highly reliable operation without causing a communication failure by monitoring the speed and voltage of a motor. SOLUTION: A converter 1 capable of performing a regenerative operation which converts the voltage of an AC power supply to a constant DC voltage, and an inverter 3, which converts a DC voltage to an AC voltage with variable frequency and variable voltage, are provided. Power running and regenerative operation is performed by lowering the DC voltage below the rated voltage in ordinary operation; and when the speed of an AC motor 4 exceeds a predetermined speed, the DC voltage is raised to a rated voltage and the regenerative operation of the converter 1 is prohibited by raising the DC voltage to a rated voltage. When performing deceleration, means 37 and 39 are provided, which perform deceleration after returning the DC voltage to a low voltage and then releases the prohibition of the generative operation of the converter 1. |
