Systems and methods for controlling capacity of a compressor

A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising:

• a vapor compression system, comprising:
• a vapor compression circuit configured to circulate a working fluid therethrough-therethough;
• and
• a compressor configured to pressurize and direct the working fluid through the vapor compression circuit, wherein the compressor comprises a pre-rotation vane (PRV) adjustable between a fully open position and a first fully closed position and a variable geometry diffuser (VGD) adjustable between a maximum allowed open position and a second fully closed position;
• and
• a controller comprising a memory and processing circuitry, wherein the memory stores instructions that, when executed by the processing circuitry, cause the processing circuitry to transition operation of the compressor between a first mode and a second mode to regulate a capacity of the compressor, wherein a first position of the VGD is independent of a second position of the PRV in the first mode, and the first position of the VGD is dependent on the second position of the PRV in the second mode.

A method for controlling a capacity of a compressor having a pre-rotation vane (PRV) and a variable geometry diffuser (VGD), the method comprising:

• determining an actual head factor for the compressor based on one or more operating conditions of a vapor compression system employing the compressor;
• determining a lift of the compressor based on a ratio of the actual head factor and a maximum head factor of the compressor;
• comparing the lift with a low lift threshold value and a high lift threshold value to generate a comparison result;
• operating the compressor in a first mode in which a position of the VGD is varied independently of a position of the PRV in response to the comparison result indicating that the lift is less than the low lift threshold value;
• and
• operating the compressor in a second mode in which the position of the VGD is varied based on a correlation between the position of the VGD and the position of the PRV in response to the comparison result indicating that the lift is greater than the high lift threshold value.