Ujjwal M. Nath, Chanchal Dey, and Rajani K. Mudi
Internal model control, PID controller, switching IMC–PID, smooth control, tight control, lag dominating process, real-time level control
A number of industrial processes are found to be lag dominating in nature. To ensure desirable responses for such processes, a switching internal model control (IMC)–proportional–integral–derivative (PID) controller is reported here. An initial setting of the proposed PID controller is obtained through IMC technique. The proposed control scheme makes online switching between smooth and tight control modes of IMC tuning depending on the current process operating conditions. Closed loop time constant (λ) and integral time (τI) of the proposed IMC–PID controller are modified with process behaviour instead of fixed settings as that of a conventional IMC–PID. Thus, due to switching, IMC–PID controller with two separate sets of values for λ and τI is expected to provide improved closed loop performance during set-point tracking and load recovery phases, respectively. Superiority of the proposed scheme is verified through simulation study on lag dominating process models. In addition to simulation study, effectiveness of the proposed switching based IMC tuning scheme is also demonstrated through real-time experimentation on a level control loop.
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