Systems and methods for driving a compressor with a motor

摘要

A system which drives a compressor of a refrigeration system. The system includes a motor having a stationary assembly and a rotatable assembly. The stationary assembly includes windings adapted to be energized in at least one preselected sequence. The rotatable assembly is in magnetic coupling relation to the stationary assembly and in driving relation to the compressor. The system further includes a circuit for sensing a back electromotive force (EMF) voltage in the windings and for generating a BEMF signal representative thereof. The BEMF signal has first and second polarities representative of position of the rotatable assembly relative to a zero crossing of the sensed back EMF voltage. The first polarity is representative of the position of the rotatable assembly past a position corresponding to the zero crossing and the second polarity is opposite the first polarity. A control circuit responsive to the BEMF signal generates a commutation signal and includes a commutation counter counting at a preset rate. The commutation counter increases its count when the BEMF signal is of the first polarity and decreases its count when the BEMF signal is of the second polarity. The control circuit further generates a corresponding commutation signal when the count reaches a preset value. The system further includes power switching devices responsive to the commutation signal for selectively connecting a power supply to the windings in the preselected sequence to produce an electromagnetic field for rotating the rotatable assembly.