| 摘要 |
A circuit and method to improve power efficiency of AC induction motors is described for adopting an AC PWM chopper method in power input controls. For a period of several seconds after initially supplying power source voltage, the starting voltage is bypassed by a relay switch to prevent malfunctioning of devices. A PWM waveform is provided by a microcomputer and it is combined with a zero crossing signal of the power source voltage. The combined signal is controlled and buffered by photo couplers, by which power source voltage is controlled with transistors of a power controller unit. A current flow through the motor is detected and store into memory of the microcomputer. In a next sequence, another PWM waveform is provided to again detect other current flow through the motor and its detected value is compared with the previous value store in the memory. These sequences are repeated to search for a minimum current value according to variation of loading on the motor.
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