当系统存在较大扰动时,锅炉的变量如蒸汽压力和汽包水位都会产生较大的波动。简单的底层控制器消除这种波动的效果不太理想。提出了两层结构控制方法来改善系统的性能。底层控制采用基于DCS(Distributed control systems)系统的预测PID控制方法,根据当前的工况,蒸汽压力和水位的设定点由基于模糊理论的监控层给出。针对一个具体的锅炉系统,改进后的方法其控制性能和经济目标均有了很大的改善。
Aiming at a class of nonlinear systems with multiple equilibrium points, we present a dual-mode model predictive control algorithm with extended terminal constraint set combined with control invariant set and gain schedule. Local LQR control laws and the corresponding maximum control invariant sets can be designed for finite equilibrium points. It is guaranteed that control invariant sets are overlapped each other. The union of the control invariant sets is treated as the terminal constraint set of predictive control. The feasibility and stability of the novel dual-mode model predictive control are investigated with both variable and fixed horizon. Because of the introduction of extended terminal constrained set, the feasibility of optimization can be guaranteed with short prediction horizon. In this way, the size of the optimization problem is reduced so it is computationally efficient. Finally, a simulation example illustrating the algorithm is presented.
