| Level control system is an important part of industrial production,and most of the current level control systems use open-loop or closed-loop PID(Proportion Integral Derivative)controllers to control the liquid level.However,in the open-loop state,PID control is easily disturbed by external interference,resulting in an unstable control system;in the closed-loop state,PID control has problems such as long adjustment time and large overshoot.In order to improve the control accuracy and stability of the liquid level control system,this thesis uses a fractional-order PID(FOPID)controller to control the liquid level.Since the fractional-order PID controller has many adjustment parameters and is difficult to be adjusted,the Whale Optimization Algorithm(WOA)is used to adjust the parameters of the fractional-order PID controller.Through simulation,the control performance of the WOA-based fractional-order PID controller for integer-order systems and fractional-order systems is investigated.Meanwhile,this thesis studies the control performance of the fractional-order PID controller based on WOA algorithm by mathematical modeling of the single-volume and double-volume water tanks.The research in this thesis focuses on the following points:For the problem of difficult parameter rectification of fractional-order PID controller,this thesis uses WOA algorithm for parameter rectification of fractional-order PID controller.Because of the shortcomings of WOA algorithm,such as low search accuracy,slow convergence speed and easy to fall into local optimal solution,this thesis proposes an adaptive hybrid strategy to improve WOA algorithm.Tent chaotic sequence is used to improve the population diversity in the early stage of search,so as to improve the search ability and convergence speed of the algorithm.In the middle stage of search,the nonlinear variation strategy of convergence factor is used,and adaptive weight is added to solve the problem that the algorithm falls into the local optimal solution.In the late stage of search,Gaussian mutation is added to improve the search accuracy of the algorithm.Based on the integer-order and fractional-order controlled objects,this thesis uses the Adaptive Mixed Strategy Whale Optimization Algorithm(AMSWOA)for fractional-order PID controller.Simulation experiments are conducted in Matlab/Simulink environment,and it is proved that the controller has excellent control performance and anti-disturbance capability for different controlled objects.Based on the AMSWOA-FOPID controller designed in this thesis,the experiment of the liquid level characteristics of the water tank is used to obtain the transfer functions of single-volume and dual-volume water tank respectively,and the simulation models of fractional-order PID controller and liquid level control system are built in MATLAB/Simulink environment and compared with the integer-order PID control algorithm.The results show that compared with the integer-order PID control algorithm,the fractional-order PID controller with adaptive hybrid strategy whale optimization algorithm applied in the liquid level control has the advantages of small overshoot,fast regulation time and small steady-state error. |
