Design and Application of a Time-Optimum Controller for a Class of Nonlinear Processes

A procedure was developed to extend time-optimum control of linear processes to a class of nonlinear processes consisting of a second-order overdamped linear process followed by a nomemory nonlinearity. Bang-bang control was combined with a proportional-integral-derivation (PID) controller to achieve time-optimum control for set-point changes and good regulator operation for minor disturbances. This dual-mode controller was implemented with a small digital computer. The settling time for step set-point changes with dual-mode control was compared to that with PID control alone. A factor of 2 improvement was achieved through time-optimum control. The dualmode control was successfully applied to an actual nonlinear process.