PURPOSE: To improve follow-up to a speed command by computing a required value of the input or outlet current from the operating command signal and the load characteristics of an electric motor, and setting it as the output value of an integrator or the primary delay factor in a voltage control part.
CONSTITUTION: Torque increases with the square of the speed in an electric motor, so it is possible to obtain a current command value which maintains speed at the time of restarting operation as an output when a speed command value is inputted in a square-law operating device 27 with coefficient. The current command value is inputted in a switch 28, and is set as the output of the operating device of a proportional integrator 17 during stopping. Because a required value to maintain a speed is given beforehand as the output of the proportional integrator 17 generated at the time of restarting operation, response delay is shortened, and the current required to maintain a speed is injected with only the response delay of the proportional integrator 20 for current control. It is thus possible to enhance the speed response characteristics of an induction motor 7 and improve it regardless of the response characteristics of the proportional integrator 17 for voltage control.
YAMAGA YOSHIHARU
KUBO KENJI
AZUSAZAWA NOBORU
