MICROPROCESSOR BASED MOTOR CONTROL SYSTEM WITH PHASE DIFFERENCE DETECTION

摘要

The present invention involves a control system for a motor having a main winding and an auxiliary winding disposed on a stator. A microprocessor determines the phase difference between the line voltage and the voltage between the main winding and the auxiliary winding to determine the rotational status of the rotor. In a moving rotor, a measurable phase difference exists. This phase difference can be measured by monitoring the zero crossings of the respective voltages. One method of measuring the phase difference is to check the logic state corresponding to the voltage between the main and auxiliary windings when a predetermined time period has elapsed after a zero crossing of the line voltage. Another method measures the time delay between the zero crossings of the two voltages. The control system of the present invention is particularly adapted for use with single phase AC motors having a main winding and an auxiliary winding disposed electrically out of phase on the stator. The control system of the present invention is also particularly adapted for use with compressors and appliances associated with a refrigeration system having a cabinet temperature detector. The refrigeration system of the present invention includes a motor housing detector to deenergize and prevent motor start if an overheat condition exits, and a user setting device to allow a user to manually add an offset to the temperature setting. Additional control functions can be easily added using extra input and output leads provided on the microprocessor.