| Liquid level control is an important part of process control and plays an important role in the field of petroleum, chemical, metallurgy and other industrial processes. Liquid level control system has the characteristics of nonlinear and uncertainty. And researching and designing the advanced control scheme and control algorithm of the liquid level system with good performance has been the focus of attention of scholars and institutions. Therefore, this paper designs the PID, fuzzy and LQR(linear quadratic regulator) control algorithm with the mathematical model of the coupled tank liquid level system. And according to these designed control method, the switching control algorithm of the liquid level system is proposed.Firstly, the mathematical model of liquid level system is established. Based on the coupled tank experimental platform, build the mathematical model of liquid level system through reading the literature materials and the research reports of the liquid level system. And the mathematical model which has been built is nonlinear. In order to solve the problem and obtain the linear model of the liquid level system, this paper expand the nonlinear mathematical model by the Taylor formula.Then, the PID control algorithm, the fuzzy control algorithm and the LQR control algorithm are proposed on the basis of the established linear mathematical model of the system. In the light of the principle of the control algorithm, the proportion, integral and differential control parameters for PID controller, the fuzzy control rules, membership function and method of solving fuzzy for fuzzy controller, the state weighting matrix and control weighting matrix for the LQR controller are designed respectively. Hence, the controller structure of every control algorithm is proposed. And the simulation results show that LQR control algorithm has the best stability for liquid level system.Finally, comparing and analyzing the three control algorithms, the fuzzy and LQR switching control scheme of liquid level system is proposed to control the instability of the system and the uncertainty of LQR control model. Through dividing the level system scope as multiple cell, the set of model and controller is established by using the “decomposition-synthesis” multi modeling strategy. And the switching rule of fuzzy and LQR control is designed on the basis of the system level feedback value. In order to ensure the stability of the system in the case of liquid level to achieve a smooth switch between the controller and the LQR and avoid the phenomenon of liquid level fluctuation during fuzzy control and LQR control switching directly, the weighted control of fuzzy and LQR is proposed. The simulation results show that the proposed control scheme has a good stability to liquid level system. |
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