Surge prevention control system for dynamic compressors
First Claim
1. A control system for avoiding surge in a dynamic compressor, the compressor having a variable operating point definable on a compressor map which includes a stable region, a surge region, a surge line separating the two regions, and a surge control line in the stable region near but displaced from the surge line, the control system comprising in combination:
- a selectively responsive anti-surge valve coupled to the compressor for controllably increasing compressor flow;
a multiple module controller for receiving a control variable indicative of the operating point of the compressor and producing a control signal for controlling the anti-surge valve;
the multiple module controller including;
a PID control module responsive to the control variable for producing a first output signal exerting control action on the operating point of the compressor between the surge control line and the surge line;
a closed loop rate control module responsive to a signal indicative of the rate of approach of the operating point to the surge control line for producing a second output signal having a magnitude which exerts control action on the operating point of the compressor to limit the rate of approach; and
,an output signal selector for selectively coupling the first or second output signal as the control signal to the anti-surge valve.
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Accused Products
Abstract
A surge prevention control system for use with a dynamic compressor provides a multiple module controller for operating an anti-surge valve to bypass flow around the dynamic compressor. The multiple module controller includes a PID control module and a rate control module. The PID control module controls the anti-surge valve to control the operating point of the dynamic compressor about the surge control line. The rate control module uses the rate of approach of the operating point to the surge control line as its process variable. In the event of high rate of approach, the rate control module takes control of the anti-surge valve. The setpoint of the rate control module is adjusted to open the anti-surge valve to control the rate of approach to the surge control line to minimize the overshoot of the PID control.
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Citations
27 Claims
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1. A control system for avoiding surge in a dynamic compressor, the compressor having a variable operating point definable on a compressor map which includes a stable region, a surge region, a surge line separating the two regions, and a surge control line in the stable region near but displaced from the surge line, the control system comprising in combination:
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a selectively responsive anti-surge valve coupled to the compressor for controllably increasing compressor flow; a multiple module controller for receiving a control variable indicative of the operating point of the compressor and producing a control signal for controlling the anti-surge valve;
the multiple module controller including;a PID control module responsive to the control variable for producing a first output signal exerting control action on the operating point of the compressor between the surge control line and the surge line; a closed loop rate control module responsive to a signal indicative of the rate of approach of the operating point to the surge control line for producing a second output signal having a magnitude which exerts control action on the operating point of the compressor to limit the rate of approach; and
,an output signal selector for selectively coupling the first or second output signal as the control signal to the anti-surge valve. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13)
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9. A control system as defined in 8, wherein the setpoint adjuster reduces the setpoint of the rate control module when a difference between the control variable and the setpoint of the PID control module decreases.
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14. A control system for avoiding surge in a dynamic compressor, the compressor having a variable operating point definable on a compressor map which includes a stable region, a surge region, a surge line separating said regions, and a surge control line in the stable region near but displaced from the surge line, the control system comprising, in combination:
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an anti-surge valve coupled to the compressor and responsive to an electrical control signal for controllably increasing compressor flow; a multiple module controller responsive to a control variable indicative of operating point of the compressor for producing said control signal, the multiple module controller including; a closed loop PID control module responsive to the control variable for exerting control action on the operating point of the compressor when said operating point is between the surge control line and the surge line; a closed loop rate control module responsive to a signal indicative of the rate of approach of the operating point to the surge control line for exerting control action on the operating point of the compressor anywhere in the compressor map when the rate of approach exceeds a given level, and selector means for passing control of the anti-surge valve between the PID control module and the rate control module. - View Dependent Claims (15, 16, 17, 18)
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19. A method for preventing surge in a dynamic compressor, the dynamic compressor having a variable operating point definable on a compressor map which includes a surge region and a stable region separated by a surge line, and a surge control line in the stable region displaced from the surge line, the method comprising the steps of:
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providing an anti-surge valve having an adjustable opening for increasing flow through the dynamic compressor; sensing process conditions in the dynamic compressor to produce a control variable indicative of the operating point of the dynamic compressor; operating a first closed loop PID to generate a first output signal for controlling the anti-surge valve to control the operating point about the surge control line; monitoring a rate of approach of the operating point to the surge control line; operating a second closed loop PID to generate a second output signal for controlling the anti-surge valve to control the rate of approach; selecting among the first and second output signals as a control signal; and adjusting the opening of the anti-surge valve according to the control signal. - View Dependent Claims (20, 21, 22, 23, 24, 25)
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26. A method for preventing surge in a dynamic compressor, the dynamic compressor having a variable operating point definable on a compressor map which includes a surge region and a stable operation region separated by a surge line, and a surge control line in the stable region displaced from the surge line, the method comprising the steps of:
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providing an anti-surge valve having an adjustable opening for increasing flow through the dynamic compressor; sensing process conditions of the dynamic compressor to produce a control variable indicative of the operating point of the dynamic compressor; performing a closed loop PID control on the anti-surge valve using the control variable as a process variable and the surge control line as a setpoint; monitoring a rate of approach of the operating point toward the surge control line; and in the event of high rate of approach, taking control of the anti-surge valve by performing a closed loop PID control using the rate of approach as a process variable. - View Dependent Claims (27)
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Specification