Abstract: A compressor drive system for controlling the gas pressure in a pressure gas volume (106) connected to the compressor (101). A brushless alternating current motor (23) is directly coupled to the compressor, which is driven with the same speed as the motor. The pressure in the gas volume (106) is sensed by pressure sensing means (109) connected to a converter (114). The converter simultaneously changes the amplitude and frequency of the drive voltage supplied to the motor (23). This is done in response to pressure changes in volume (106). The motor is stopped if the pressure exceeds a preset maximum value. A pressure gas container (104) is depressurized at motor stop to allow restarting without counter pressure on the compressor. Means (44) for controlling the amplitude and frequency of the drive voltage is provided so that the normal speed maximum load current is never exceeded during motor start.

Abstract: Method and apparatus for controlling the operation of a motor driven compressor which is automatically unloaded when the receiver pressure reaches a predetermined maximum level and loaded when the receiver pressure reaches a predetermined minimum level by means of pressure actuated electric control means which are time delayed to start and stop the compressor motor and the unloading and loading operation in accordance with predetermined mode of operation.