Simple Anti-Windup Controllers

The paper describes digital implementation of proportional, integral, and derivative (PID) compensators for a class of multiple-input multiple-output dynamic systems to regulate actuators in a coordinated manner. In practice, actuators of systems to be controlled are constrained to preset operating ranges. Integrator windups can occur if any of the actuators saturate and the controller continues to integrate the errors. The situation can often lead to a significant performance degradation and may result in unstable operation. A systematic approach is presented to implement a multivariable controller that is free from integrator windup. The concept is based on conditional integration and coordination to avoid windup in any of the integrators. The method is applicable to a digital multivariable controller with lead and lag actions. The concept has been demonstrated on a resaturator in the integrated gassification combined cycle (IGCC) process evaluation facility.