Methodology and Algorithms for Protecting Centrifugal and Axial Compressors from Surge and Choke

Abstract

This disclosure describes a novel methodology for anti-surge and anti-choke control systems protecting centrifugal and axial compressors. The methodology, based on Buckingham's π-theorem for compressors, presents compressor performance maps in dimensionless rectangular π-term coordinates that are independent of compressor inlet conditions, fluid molecular weight and rotational speed. The full range of compressor operating points from surge to choke is monitored and controlled when surge and choke limits are available. This is accomplished by converting rectangular coordinates presented in π-terms to polar coordinates, and then converting them to a controlled variable used in the closed-loop controllers. The methodology provides control algorithms for variable speed compressors, variable geometry compressors equipped with inlet guide vanes or stator vanes that exhibit displacement of surge and choke limits. The methodology most accurately estimates the location of the operating point relative to its limit in polar coordinates if only the surge or choke limit is available. The presented protection methods are applicable to any known types of dynamic compressors for industrial, commercial, jet engines, turbochargers.

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         19 . A method for controlling the operation of a centrifugal or axial compressor equipped with automatic control systems that continuously calculate system parameters, said method comprising:
 reading one or more input signals from one or more sensors;   converting a compressor performance map comprising one or more surge points which define a first boundary condition into a compressor flow function in rectangular coordinates of flow Mach number and total pressure ratio;   applying said compressor flow function to each of said one or more surge points;   converting said one or more surge points of said first boundary condition to polar coordinates at a constant angle;   measuring an operating point of the centrifugal or axial compressor via said input signals from said one or more sensors;   calculating a control variable in polar coordinates;   calculating an error value from a difference between a set point and said control variable in polar coordinates; and   sending a control signal to a compressor control mechanism such that said control variable is moved closer to said set point to reduce said error value.   
     
     
         20 . The method of  claim 19 , wherein said compressor flow function comprises a total pressure ratio function; and
 applying said total pressure ratio function to each of said one or more surge points to define an altered coordinate of flow Mach number.   
     
     
         21 . The method of  claim 19 , wherein said compressor flow function comprises a flow Mach number function; and
 applying said flow Mach number function to each of said one or more surge points to define an altered coordinate of total pressure ratio.   
     
     
         22 . The method of  claim 19 , wherein said compressor control mechanism comprises a mechanism selected from the group consisting of an anti-surge valve and an outlet valve. 
     
     
         23 . A method for controlling the operation of a centrifugal or axial compressor equipped with automatic control systems that continuously calculate system parameters, said method comprising:
 reading one or more input signals from one or more sensors;   converting a compressor performance map comprising one or more choke points which define a second boundary condition into a compressor flow function in rectangular coordinates of flow Mach number and total pressure ratio;   applying said compressor flow function to each of said one or more choke points;   converting said one or more choke points of said second boundary condition to polar coordinates at a constant angle;   measuring an operating point of the centrifugal or axial compressor via said input signals from said one or more sensors;   calculating a control variable in polar coordinates;   calculating an error value from a difference between a set point and said control variable in polar coordinates; and   sending a control signal to a compressor control mechanism such that said control variable is moved closer to said set point to reduce said error value.   
     
     
         24 . The method of  claim 23 , wherein said compressor flow function comprises a total pressure ratio function; and
 applying said total pressure ratio function to each of said one or more choke points to define an altered coordinate of flow Mach number.   
     
     
         25 . The method of  claim 23 , wherein said compressor flow function comprises a flow Mach number function; and
 applying said flow Mach number function to each of said one or more choke points to define an altered coordinate of total pressure ratio.   
     
     
         26 . The method of  claim 23 , wherein said compressor control mechanism comprises a mechanism selected from the group consisting of an outlet valve, a variable inlet guide vane controller, and a variable stator vane controller.