System and method for protecting a single phase motor from circulating currents

摘要

A single phase motor system and method for preventing excessive circulating currents in the motor. The motor has a power supply link including power switches responsive to a motor control signal for connecting the motor winding to a power supply in alternating on and off intervals. A current sensing circuit senses current in the power supply link during the on intervals. A current regulation circuit generates a current regulation signal representative of the difference between the sensed current and a peak regulated current level that is a function of desired motor speed and/or torque. An overcurrent circuit generates an overcurrent signal in response to the sensed current exceeding a maximum current level greater than the peak regulated current level. The motor also has a control circuit responsive to the current regulation signal for generating the motor control signal thereby to regulate current in the winding and control the motor speed and/or torque. At least one of the on intervals is greater than or equal to a minimum interval which is independent of the current regulation signal. The control circuit is also responsive to the overcurrent signal for causing the power switches to disconnect the winding from the power supply thereby to prevent excessive currents from circulating in the motor.