DIRECT-CURRENT DAMPING OF INDUCTION MOTOR BY USE OF INVERTER

摘要

PURPOSE:To avoid the phenomenon of reverse rotation of a rotor near a state of stoppage by a method wherein a pulse-shaped output direct-current voltage of an inverter for driving an induction motor is subjected to a step-down control in accordance with the number of revolutions of a rotating system of the induction motor at the time of damping of the rotating system. CONSTITUTION:When a direct-current impression voltage is changed over in two stages from a high voltage to a low one in accordance with the number of revolutions in direct-current damping, the number N of revolutions is lowered by the direct-current damping in conformity with a damping torque curve L1h at a direct-current impression voltage Va11. When the number Ns of revolutions is reached at the time ts, a change-over is made to a voltage Va12 lower than the voltage Va11, and the direct-current braking in conformity with a braking torque curve L1n is conducted till stoppage. Accordingly, the phenomenon of reverse rotation of a rotor can be avoided. In the case when the number N of revolutions at the time point of start of the direct-current damping is prescribed and a time required for the number of revolutions to lower to the number Ns of revolutions can always be estimated, the change-over of the direct-current impression voltage can be made at the time ts. Besides, a control is executed by CPU of a control circuit of an inverter with the detected number of revolutions or the time elapsed used as parameters.