A candidate to replace PID control: SISO-constrained LQ control

It is commonly believed that for single-input/single-output (SISO) systems, well-tuned proportional, integral, derivative (PID) controllers work as well as model-based controllers and that PID controllers are more robust to model errors. In this paper we present a novel offset-free constrained linear quadratic (LQ) controller for SISO systems, which is implemented in an efficient way so that the total controller execution tine is similar to that of a PID. The proposed controller has three modules: a state and disturbance estimator, a target calculation, and a constrained dynamic optimization. It is shown that the proposed controller outperforms PID both in setpoint changes and disturbance rejection, it is robust to model errors, it is insensitive to measurement noise, and it handles constraints better than common anti-windup PID. Tuning the proposed controller is simple. In principle there are three tuning parameters to choose, but in all examples presented only one was actually varied, obtaining a clear and intuitive effect on the closed-loop performance. (c) 2005 American Institute of Chemical Engineers