Nonlinear PID Pressure Control Based on Extremum Seeking

摘要

Rear-cabin pressure control system of high-altitude test facility has the characteristics of large time-delay, nonlinearity and strong disturbances. In China, the rear-cabin pressure control system uses the conventional PID control method which can't nonlinearly regulate pressure very well; especially in engine transient experiments, it can't automatically turn PID parameters to adapt the changes of system's nonlinearities, which has seriously affected the dynamic regulation and control accuracy of the rear-cabin pressure. Therefore, in this paper, firstly the dynamics of hydraulic butterfly valve is modeled and the nonlinear characteristics of exhaust diffuser are analyzed and the simulation model of the rear-cabin pressure control system is established. Secondly, the nonlinear PID controller is developed based on extremum seeking and its parameters are turned online according to the pressure errors between the setting valves and system outputs of the pressure system by minimizing the cost function. Finally, with and without engine flow disturbances, some simulation results of the linear and nonlinear PID control are given for pressure regulation to show that the proposed nonlinear PID based on extremum seeking can not only turn the controller parameters online, but also reject time-varying and large amplitude disturbances, so it has effectively enhanced the nonlinear adaptability of controller and improved the control accuracy of transient responses of the rear-cabin pressure control system.