PID controller design for disturbed multivariable systems

A linear-quadratic-regulator-based (LQ-regulator-based) design methodology is proposed to design proportional-integral-derivative (PID) controllers for multivariable systems with load disturbances. Except for a few parameters that are preliminarily selected, most of the PID parameters are systematically tuned using the developed plant state-feedback and controller state-feedforward LQR approach, such that satisfactory performance with guaranteed closed-loop stability is achieved. In order to access the plant state variables and carry out disturbance rejection, an observer-based disturbance rejection technique is proposed, which through an ´equivalent disturbance´ concept, retains the observation error to be used for disturbance compensation. This makes disturbance measurement unnecessary and the disturbance rejection tuning independent of the set-point response adjustment. A robust stability analysis is also included for the modelling error. An illustrative example is given for comparison with alternative techniques.