Patent ID: 6055459
Filing Date: 2000-04-25
Classification: G05B

Abstract:
A method for preventing windup of a PID controller, said PID controller used in the control loop of a process control system, said PID controller arranged to produce and output within a current execution cycle, a Control Variable (CV) to a device controlling a process and to receive within said current execution cycle a Process Variable (PV) from the control loop indicative of the state of the controlled process, a setpoint (SP), and a nonlinear gain parameter (K) from the process control system, said method comprising the steps of:a) Receiving said PV from said control loop, said SP, and said K from said process control system during said current execution cycle and generating a proportional component of the deviation of said PV from said SP;b) Receiving said PV from said control loop, said SP and said K from said process control system during said current execution cycle and generating an integral component that is the time integral of the deviation of said PV from said SP;c) Receiving said PV from said control loop, said SP, and said K from said process control system during said current execution cycle and generating a derivative component that is the time derivative of the deviation of said PV from said SP;d) Generating an incremental output CV for the current execution cycle with said proportional, integral, and derivative components;e) Generating a nonlinear gain change component and adding said nonlinear gain change component to said incremental output CV;f) Generating an output CV for said current execution cycle by adding the product of step e) to the output CV value of the previous execution cycle; and,g) Updating a stored sum of proportional, integral, and derivative components of the previous execution cycles with said proportional, integral, and derivative components of the current execution cycle.