초록 ▼

An apparatus and method controls the speed of an AC induction motor by varying the frequency and current to the motor from an inverter power supply. A Counter EMF regulator receives a reference signal corresponding to the desired speed, and a signal proportional to CEMF for feedback. The output of t

An apparatus and method controls the speed of an AC induction motor by varying the frequency and current to the motor from an inverter power supply. A Counter EMF regulator receives a reference signal corresponding to the desired speed, and a signal proportional to CEMF for feedback. The output of the CEMF regulator is provided to the power supply to control the current to the motor. The CEMF feedback signal is also utilized to vary the output frequency of the power supply in accordance with the magnitude of the CEMF. This maintains the magnetizing component of stator winding current at a constant value for all operating frequencies of the motor. A signal corresponding to the load current component of the stator winding adds to the speed reference signal to the CEMF regulator to increase CEMF and frequency with increasing load, thereby to compensate for increased slip and maintain constant speed. The phase displacement between CEMF and stator winding current is determined. If the phase displacement is less than 90°, the motor is in the motoring condition and the frequency of the power supply is determined solely by the CEMF. If the phase displacement is greater than 90°, the motor is regenerating, and the frequency of the power supply is increased to prevent regeneration, and to avoid the need for the power supply to absorb regenerative energy.

대표청구항 ▼

A control for controlling the speed of the rotor of an AC induction motor and avoiding regenerative operation of the motor; said motor having a stator winding electromagnetically coupled to the rotor, the stator winding having input terminals by which the motor is coupled to an AC power means; the A

A control for controlling the speed of the rotor of an AC induction motor and avoiding regenerative operation of the motor; said motor having a stator winding electromagnetically coupled to the rotor, the stator winding having input terminals by which the motor is coupled to an AC power means; the AC power means providing a stator winding current having an operating frequency to the stator winding of the motor, the magnitude of the stator winding current and its operating frequency being determined by current command and frequency command signals, respectively, for the AC power means; there being a synchronous speed of the motor corresponding to the operating frequency of the stator winding current, said control comprising: means for providing a signal corresponding to the desired speed of said motor; means for providing a signal corresponding to the CEMF developed in the stator winding as a result of the flow of the magnetizing current component of the stator winding current through the stator winding, said CEMF signal comprising a frequency command signal for the AC power means for varying the operating frequency of the stator winding current in direct proportion to the magnitude of the CEMF signal, so that the magnetizing current component of the stator winding current, and thus the stator flux, may be maintained at a constant value at all operating frequencies; regulating means having input means receiving said desired speed signal as a reference signal and said CEMF signal as a feedback signal, said regulating means having an output providing a signal for the AC power source that comprises the current command signal for establishing the magnitude of the stator winding current; means for ascertaining the load current component of the stator winding current and providing a signal proportional to the magnitude thereof, said load current component signal being applied to said input means of said regulating means in a manner additive to said desired speed signal; means for determining whether the phase displacement between the CEMF and the stator winding current is less than, or greater than, a predetermined phase displacement amount, said predetermined phase displacement amount being the phase displacement existing between the CEMF and the stator winding current when the speed of the rotor is at the synchronous speed of the motor; and means for allowing the frequency command signal for the AC power means to be determined solely by the magnitude of the CEMF signal when the phase displacement between the CEMF and the stator winding current is less than the predetermined phase displacement amount and for increasing the frequency command signal for the AC power means when the phase displacement between the CEMF and the stator winding current is greater than the predetermined phase displacement amount, thereby increasing the operating frequency of the stator winding current and avoiding regenerative operation of the motor.