Actuator Rate Limit Effects on Proportional-Integral Controller for First-Order Plus Time-Delay Systems

Actuator rate limit deteriorates control performance with amplitude attenuation and phase delay, and may lead to system instability in process control. In this paper, great challenges for first-order plus time delay (FOPTD) systems are concerned. Based on the preliminary knowledge of the definition of rate limiter, the concept of closed-loop onset frequency with rate limiter and classic proportional-integral (PI) tuning rules, the rate limit effects on PI controller are analyzed by simulations. The results show that the rate limiter has significant influence on the stability regions of PI parameters which can be reduced greatly. Besides, PI tuning rules with the same robustness constraint can be obviously effected where Skogestad internal model (SIMC) tuning rule is more robust to the rate limit variation than that of maximize the integral gain (Åström) and robustness constrained optimization (DRO) tuning rule. These results can offer a guideline to tune PI parameters when actuators have non-ignorable rate limit for industrial applications.