Abstract: A method for controlling working fluid surge in a centrifugal compressor. According to the method, surge detection is accomplished by calculating the change in the compressible fluid mass flow rate that accompanies surge in a compressor, the compressor having means for sensing a first fluid temperature, means for sensing a first pressure, means for sensing a second pressure, and means for measuring current drawn by a compressor prime mover, the method comprising the steps of: calculating the time rate of change of the first fluid temperature; calculating the time rate of change of the first fluid pressure; calculating the time rate of change of the second fluid pressure; calculating the time rate of change of current drawn by the compressor prime mover; calculating the mass flow rate by combining the calculated rates of change; and comparing the calculated mass flow rate to a predetermined acceptable mass flow rate to determine if surge is present.

Abstract: A method for detecting the occurrence of surge in a centrifugal compressor includes the step of calculating a time rate of change of a discharge pressure of the fluid discharged from the compressor. In one preferred embodiment, the time rate of change of the discharge pressure is calculated by initially setting PREV PRESS and RATE PRESS variables equal to zero (0), and commencing a RATE PRESS subroutine having a time limit for cycling therethrough. The RATE PRESS subroutine includes the steps of obtaining a discharge pressure reading for the fluid discharged from the compressor, subtracting the discharge pressure reading from the PREV PRESS variable to establish the RATE PRESS variable, and resetting the PREV PRESS variable equal to the value of the discharge pressure reading. After the RATE PRESS variable has been determined, the RATE PRESS is compared with an acceptable set time point rate of change for the discharge pressure.