Research On Constrained Generalized Predictive Control Strategy For Three-level Air Tank Pressure System

The pressure vessel is one of important equipments in the process industry. Three-level air tank pressure system has a large inertia, time variability and time delay, so it is a difficult process control problem. In the system, the electric implementing agencies and detection device, such as valves and instruments, are constrained, the control accuracy and anti-interference ability of traditional generalized predictive control and PID cannot meet the production requirements, so this paper proposes a constrained generalized predictive control method to overcome its shortcomings. In this algorithm, the system parameter estimates are identified by RLS, and the prediction model is obtained by solving the Diophantine equations, and then the optimal control law is calculated by using the quadratic programming as rolling optimization strategy.Firstly, according to the structure of the three-level gas tank pressure control system, the author use the mechanism modeling method to develop a mathematical model of the pressure system, using the residual method to get the system order and the forgetting factor RLS algorithm to identify system parameters on the base of experimental data, hence we can calculate the system discrete difference model. Then we use constrained generalized predictive control method to control the pressure of the three-level air tank. The control strategy can improve the control accuracy of the system, the response speed and anti-interference ability.Finally, we can verify that the method is available on the basis of the three-level air tank pressure control system. The programming of system is built on Rockwell’s configuration programming software. Through communication between host computer and ControlLogix by industrial Ethernet and OPC protocol, the pressure signal collected by ControlLogix system is sent to the host computer, and then the calculation results of constrained generalized predictive control algorithm in SIMLINK can send back to the I/O port of ControlLogix system to fulfill the control of the air pressure. By physical experiments, comparing the results with other methods, the system performance is significantly improved.