document: Robust self-tuning PID controller for nonlinear systems In this paper , we propose a robust self-tuning PID controller suitable for nonlinear systems . The control system employs a preload relay -LRB- P_Relay -RRB- in series with a PID controller . The P_Relay ensures a high gain to yield a robust performance . However , it also incurs a chattering phenomenon . In this paper , instead of viewing the chattering as an undesirable yet inevitable feature , we use it as a naturally occurring signal for tuning and re-tuning the PID controller as the operating regime digresses . No other explicit input signal is required . Once the PID controller is tuned for a particular operating point , the relay may be disabled and chattering ceases correspondingly . However , it is invoked when there is a change in setpoint to another operating regime . In this way , the approach is also applicable to time-varying systems as the PID tuning can be continuous , based on the latest set of chattering characteristics . Analysis is provided on the stability properties of the control scheme . Simulation results for the level control of fluid in a spherical tank using the scheme are also presented
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extractive_keyphrases: nonlinear systems preload relay robust performance chattering phenomenon naturally occurring signal operating regime stability properties simulation results spherical tank
abstractive_keyphrases: robust self-tuning pid controller controller tuning controller re-tuning relay disabling time-varying systems continuous tuning fluid level control