Power factor control system for inverter-driven a-c induction motor
AssigneeBorg-Warner Corporation
InventorEdward C. Siemon
Life of this patent
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Abstract
The power factor in an inverter-driven induction motor is held relatively constant at a desired optimum value, despite variations in mechanical loading on the motor, by monitoring the d-c bus current to determine the ratio of real and reactive currents, thereby to detect the actual power factor. The actual and desired power factors are then effectively compared and the resulting error signal is fed back to the inverter's d-c power supply to adjust the inverter output voltage to change the reactive current to the extent necessary to maintain the desired power factor.
Claims9
A control system for controlling the power factor in an a-c induction motor driven by the output a-c voltage from an inverter which in turn is energized by a d-c voltage received over a d-c bus from a d-c power supply, the d-c bus current alternately flowing through the inverter to the motor as real current and back from the motor and through the inverter to the d-c power supply as reactive current, said control system comprising:
- means for sensing the d-c bus current and developing therefrom an alternating voltage which varies around a zero axis and reflects the actual power factor in the induction motor, the voltage above the zero axis representing the real current to the motor while the voltage below the axis represents the reactive current from the motor;
- means for providing a reference voltage representing the desired power factor in the induction motor;
- means for comparing said alternating voltage with said reference voltage to produce an error voltage which varies as a function of the difference between the desired power factor and the actual power factor;
- and control means responsive to said error voltage for varying the amplitude of the a-c inverter voltage to change the reactive power in order to maintain the desired power factor.
Dependencies are inferred from the claim text.