Abstract: A stability control algorithm is provided for a centrifugal compressor. The stability control algorithm is used to control a variable geometry diffuser and a hot gas bypass valve (when provided) in response to the detection of compressor instabilities. The stability control algorithm can adjust the position of a diffuser ring in the variable geometry diffuser in response to the detection of a surge condition or a stall condition. In addition, the diffuser ring in the variable geometry diffuser can be adjusted to determine an optimal position of the diffuser ring. The stability control algorithm can also be used to open a hot gas bypass valve in response to the detection of continued surge conditions.

Abstract: A control system is provided to determine when to use additional compressors in a multiple compressor refrigeration system during a pull down operation. The control system determines the rate of change of the difference between the leaving chilled water temperature and a setpoint temperature during the pull down operation of the refrigeration system. If the determined rate of change of the leaving chilled water temperature difference provided by the current configuration of the refrigeration system is not adequate, then an additional compressor of the refrigeration system can be started to obtain a better rate of change. The control system can repeat this evaluation of the determined rate of change of the leaving chilled water temperature difference until all compressors in the multiple compressor refrigeration system are used.

Abstract: A control system is provided to maintain stable operating conditions for centrifugal compressors operating in parallel when one of the centrifugal compressors enters into an unstable operating condition. The control system determines an unstable operating condition in response to signals indicating the motor current or power consumption of each compressor and the position of the pre-rotation vanes of the compressors. Once an unstable operating condition is determined, the control system closes the pre-rotation vanes to each compressor until the unstable operating condition has been corrected.

Abstract: A control system is provided to maintain stable operating conditions for centrifugal compressors operating in parallel when one of the centrifugal compressors enters into an unstable operating condition. The control system determines an unstable operating condition in response to signals indicating the motor current or power consumption of each compressor and the position of the pre-rotation vanes of the compressors. Once an unstable operating condition is determined, the control system closes the pre-rotation vanes to each compressor until the unstable operating condition has been corrected.