Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1995-06-13
1997-05-13
Cabeca, John W.
Electricity: motive power systems
Induction motor systems
Primary circuit control
318802, H02P 541
Patent
active
056295987
ABSTRACT:
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 voltage on a DC bus in the inverter power supply is compared to a reference signal, the magnitude of which corresponds to the voltage on the bus when the motor is operating at synchronous speed. If the bus voltage is less than the reference voltage, the motor is in the motoring condition and the frequency of the power supply is determined by the CEMF. If the bus voltage is greater than the reference voltage, 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.
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