Modified Smith fuzzy PID temperature control in an oil-replenishing device for deep-sea hydraulic system

With the characteristics of large inertia, large time delay and time-varying parameters, it is difficult to control accurately the oil heating process in an oil-replenishing device for deep-sea hydraulic system. Four temperature control methods are presented and compared in this paper, i.e. proportional–integral–derivative controller(PID controller), fuzzy PID controller, Smith fuzzy PID controller and modified Smith fuzzy PID controller which adds a first order filter in the Smith predictor. They are simulated in MATLAB/SIMULINK based on the cases of transfer function matching and mismatching between the theoretical and the actual model. The results show that, in both cases, the step response curve of the modified Smith fuzzy PID controller has neither the significant oscillation nor the overshoot and requires the minimum time to achieve stabilization as well. Furthermore, this paper applies those four control methods in actual oil heating temperature control process through PIC16F877A micro controller unit (MCU). The experimental data demonstrate that the oil heating system controlled by the modified Smith fuzzy PID controller could stabilize at the expected temperature with nearly no overshoot, which further proves that the modified Smith fuzzy PID controller is able to sufficiently meet the challenges of industrial applications containing varying system parameters.