Abstract: A new technique of designing a robust PID and Polynomial controller for DC motor speed control is proposed. The proposed approach poses the design problem as fixed structure robust controller and mixed sensitivity H_∞ method. Performance weights are designed based on the closed-loop objective and performance requirements which are normally applied in H_∞ optimal control. Further Genetic Algorithm (GA) is adopted to solve the optimization problem for finding the optimal controller by selection of PID and polynomial parameters. Usually in literature, comparison has been carried out based on time domain performance indices; whereas, in this work, mixed sensitivity H_∞ method is considered as the fitness function for the GA techniques in order to assess the robustness of the designed system. Also, comparison of fixed structure PID and Polynomial controller is done for DC motor speed control. The proposed technique can solve the problem of complicated and high order controller of conventional H_∞ optimal control for practical use.

Keyword: DC Motor, genetic algorithm, H-infinity synthesis, robustness, MATLAB