Method for preventing windup in PID controllers employing nonlinear gain

摘要

A method of preventing windup in a PID controller when using a nonlinear gain parameter is disclosed that is used in the PID controller of a process control system. The PID controller is arranged to produce within a current execution cycle a Control Variable (CV) to a device that is controlling a process responsive to an input Process Variable (PV), a setpoint (SP), and a gain parameter (K). The present invention receives the PV, the SP, and the K and generates a proportional, integral, and derivative component of the deviation of the PV from the SP. The components so generated are used to calculate an incremental output CV for the current execution cycle. A current value of gain is next calculated by subtracting the value of the gain for the current cycle from the value of the gain from the previous cycle. Testing for a linear or nonlinear gain parameter is done next and, responsive to a nonlinear gain parameter, a nonlinear gain change component is calculated and added to the incremental output CV. An output CV is generated for the current execution cycle by adding the incremental output CV modified by the nonlinear gain change component to the CV value of the previous execution cycle. The accumulated sum of proportional, integral, and derivative components of previous execution cycles are updated with the proportional, integral, and derivative components generated by the current execution cycle. These accumulated values will be used in calculating the nonlinear gain change component in the next cycle. However, if the testing identifies a linear gain parameter, the nonlinear gain change calculation is skipped and the output CV is generated by adding the incremental output CV to the CV value of the previous execution cycle.