Position control of a pneumatic servo system by genetic algorithm based fixed-structure robust H_∞ loop shaping control

Robust controller designed by the conventional H_∞ optimal control is complicated and high order. It is not easy to implement this controller in practical works. In industrial applications, simple structure such as lead-lag compensator and PID are widely used, because of their simple structure, less number of tuning parameters, and lower order. However, tuning of these control's parameters to achieve a good performance and robustness is difficult. To solve this problem, we propose an algorithm, a genetic algorithm based fixed-structure robust H_∞ loop shaping control, to design the robust controller. Infinity norm of transfer function from disturbance to output is subjected to be minimized via searching and evolutionary computation. The resulted optimal parameters make the system stable and also guarantee robust performance. We applied the evolutionary robust controller to a pneumatic servo system. For performances comparison, three controllers; PID with derivative first order filter controller, PI controller and H_∞ loop shaping controller are investigated. Several advantages of simple structure, robustness against parameters changing is clearly shown in experimental results. Simulations are also done to prove the effectiveness of the proposed technique.