Topics in the design, analysis and implementation of feedback control systems

Abstract

<p>This thesis investigates the design, analysis and implementation of feedback control systems. A new definition of robustness for continuous feedback control systems is advanced: the region of the joint allowable variation in the gain and the dead-time of the process. This region is constructed from the open loop system frequency response. The continuous time Proportional-Integral-Derivative (PID), Internal Model Control (IMC) and Linear Quadratic Optimal Control (LQOC) design procedures for a first order plus dead-time process are compared for Integral Square Error (ISE) performance when tuned for the same level of robustness. The order from highest to lowest performance is: PID, IMC, LQOC. The robustness analysis method is used to explain the adverse effects of dead-time compensation on robustness. The continuous ISE performance of the discrete LQOC, and State Deadbeat IMC controllers are compared as the size of the control interval is changed; which one is better is shown to depend on the choice of the control interval. A new modified LQOC controller and a new Extended Horizon controller are proposed. The robustness analysis developed for continuous systems is extended to discrete systems as the region of joint allowable variation in the process gain and quasi dead-time. This region is constructed from the discrete open loop frequency response. The state deadbeat IMC with an augmented filter, and modified LQOC controllers are shown to have better ISE performance than the LQOC controller when tuned for the same level of robustness. A procedure is presented for saturation correction in multivariable one-step optimal controllers. A simultaneous correction is included which adjusts the remaining control inputs if some inputs saturate. The procedure is applicable to all related controllers including IMC. Results on saturation correction for PID controllers are also presented.</p>