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在工业生产中,液位控制占据着重要的地位,对产品的质量以及生产的安全有着重大的影响。液位控制作为一种均匀控制有2个矛盾的控制目标:既要求流出率的变化尽量平稳,又需要保证液位的稳定。并且,在设计液位控制器时,还要同时考虑它的设定值跟随特性以及干扰抑制特性。随着控制理论的不断发展,二自由度控制的概念被提出,并得到了迅速发展。应用二自由度控制的方法来控制液位不仅可以满足均匀控制的2个目标并且可以实现对设定值跟随特性和干扰抑制特性的解耦。本文首先对一种二自由度液位控制器进行了研究,分析了其工作原理以及参数整定的方法,讨论了模型误差以及死区时间对于控制效果的影响。而后,针对控制器参数解耦不完全的缺陷,通过将内模控制与二自由度液位控制器结合,提出了改进的二自由度控制方案,改进了控制器结构。根据新的控制器结构推导出了相应的参数整定方法,实现了控制器参数的完全解耦。同时,与原控制器相比,在保证均匀控制目标最优的情况下,改进控制器的参数整定更加简单,并且参数的调节更加灵活。最后,应用MATLAB对比了2种控制器的仿真结果,验证了改进控制器的控制效果。
In industrial production, the level control occupies an important position, the quality of the product and the safety of production has a significant impact. Level control as a uniform control has two contradictory control objectives: both require changes in the outflow rate as smooth as possible, but also to ensure the stability of the liquid level. And, in the design of liquid level controller, but also to consider its set point to follow the characteristics and interference suppression characteristics. With the continuous development of control theory, the concept of two degrees of freedom control has been proposed and has been rapidly developed. The application of two-degree-of-freedom control to control the liquid level not only satisfies the two objectives of uniform control but also decouples the setting-following and disturbance-rejection characteristics. In this paper, a two-degree-of-freedom liquid level controller is firstly studied, its working principle and parameter setting method are analyzed, and the influence of model error and dead time on the control effect is discussed. Then, in order to solve the problem of incomplete decoupling of controller parameters, an improved two-degree-of-freedom control scheme is proposed by combining the internal model control with the two-degree-of-freedom liquid level controller, and the controller structure is improved. According to the new controller structure, the corresponding parameter tuning method is deduced and the controller parameters are completely decoupled. At the same time, compared with the original controller, it is simpler to improve the parameter setting of the controller under the condition that the goal of uniform control is guaranteed, and the parameter adjustment is more flexible. Finally, the simulation results of two kinds of controllers are compared with MATLAB and the control effect of the improved controller is verified.