On the Impact of Plant Model and Controller Sophistication on Performance of Disturbance Attenuation and System Robustness

In the paper the problem of disturbance attenuation performance in single-loop control system is investigated. Modified MV control strategy with bounded control variance is used as benchmark for both LQG and classically and optimally tuned PID-type controllers. Certain time and frequency domain functions are then examined to further assess the control performance in terms of robustness. It has been shown that as long as the system to be controlled is delay-free, and there is no extreme demand on performance, simple lag-delay system model along with optimally tuned PID control algorithm provides control quality similar to that of LQG controlled original system assuming the same bound on control signal variance. Although the classical performance measure based on substitute delay indicates then almost optimal performance, there is still room for additional improvement that can be attained using both PID and LQG controllers and more sophisticated original delay-free model. The price paid is much larger control variance. It is interesting to note that while LQG systems remain robust this is not longer valid for PID controllers