Variable speed compressor control with sound-controlled defrost mode

A drive controller for a motor of a compressor, the drive controller comprising:

• a drive circuit that applies voltages to windings of the motor;
• a speed control module that controls the drive circuit to rotate the motor at a requested speed;
• a speed determination module that generates the requested speed;
• and
• a defrost module that enables a defrost mode in response to a defrost command received from a system controller, wherein:
• in response to the defrost mode being enabled, the speed determination module ramps the requested speed down from a speed demand to a defrost speed,
• while the defrost mode is enabled, the drive circuit continues to rotate the motor and the system controller actuates a refrigerant reversing valve to a first position,
• in response to the requested speed reaching the defrost speed, the speed determination module maintains the requested speed at the defrost speed until conclusion of the defrost mode, and
• in response to conclusion of the defrost mode, the system controller actuates the refrigerant reversing valve to a second position and the speed determination module ramps the requested speed up to the speed demand.