Nonlinear PID Control For Three-tank Water

As an abstract and typical model of industrial production process, three-tank water can be used to simulate the characteristics of first order or multiple order, linear or nonlinear, single-capacity or multiple-capacity, coupling or non-coupling industrial processes, and verify the validity of various control strategies, so that it is of an important theoretical significance and application value to study control of three-tank water.In this thesis, based on the analysis of the structure and mechanism for three-tank water, the nonlinear mathematical model of the three-tank water is established, and according to its flow characteristics, variable parameter PID is designed by using the piecewise linearization method. Simulation results indicate that the control strategy has poor dynamic and steady performance under large variation in set water level. Nonlinear variable parameter PID and nonlinear fuzzy PID are put forward to overcome the drawback of variable parameter PID. By the introduction of nonlinear characteristics, these two controllers use the PI with different parameters under a larger change in water level set, and use nonlinear variable PID or fuzzy PID under a smaller set level variation to speed up the dynamic adjustment process and to ensure steady regulation accuracy. Simulation and experimental results show the "coarse tuning" and "fine tuning" of nonlinear variable parameter PID and nonlinear fuzzy PID control have been achieved under a larger variation in water level set, and verify the correctness and feasibility of the control strategies proposed in the thesis.