摘要
常规PID控制作为一种传统的控制方法,以其计算量小、实时性好,易于实现等特点广泛应用于过程控制。然而在实际的应用中,许多被控过程机理复杂,具有高度非线性、时变性和不确定性等特点,在噪声、负载扰动等因素的影响下,过程参数甚至模型结构均会随时间和工作环境的变化而变化。此外,随着现代工业化生产的飞速发展,在进行过程控制系统设计时,除要求系统具有较高的稳定性和动、静态品质指标外,还必须保证系统具有良好的鲁棒性(Robustness)。在这种情况下,传统的基于线性化的PID控制往往难以获得最佳的控制效果。
对PID控制器的设计和应用,核心问题是PID参数的整定。如何在被控对象的实际变化状况下,解决静态与动态性能之间、跟踪设定值与抑制扰动之间、鲁棒性与控制性能之间的矛盾,成为众多研究者和生产者非常关注的课题。为了解决这个问题,人们提出了大量的理论和改进技术,众多的PID参数整定方法不断涌现。
本文以非线性控制系统PID参数整定为工程背景,以PID参数的优化设计为目标,在分析和研究国内外PID参数先进整定方法的基础上,运用相关分析实验统计方法建立对象的数学模型——传递函数,把PID参数设计问题转化为一种非线性优化设计问题,借助于约束条件下的优化算法,以非线性最小平方指标为目标函数,将非线性约束优化算法同Simulink仿真技术相结合,找出符合控制系统品质指标的一组调节参数。对优化设计作鲁棒性仿真研究,通过二阶模型和三阶模型仿真实验,比较不同的控制结果,验证本优化设计方法不仅使非线性系统满足性能指标要求,具有良好的控制特性,而且还有较强的鲁棒性。
最后,在仿真系统初步实现的基础上,提出下一步的研究和改进方向。
Ordinary PID control as a traditional control method is used in process control widely because of its small computation, good real-time and the easiness to realize.
However, in real practice, many of the mechanisms of controlled process are complex, highly nonlinear, time-varying and uncertain. In the influence of noise and load disturbance, process parameter and even model structure will change with the variation of time and work condition. In addition, with the rapid development of modern industrialize, when designing process control system, both the higher stability and dynamic static performance, as well as the good robustness are demanded .In the case, the traditional PID control, which is based on linear, is often hard to obtain the optimal control effect.
As for the design and usage of the PID controller, the core problem is PID parameter tuning. When the controlled subject changes, how to deal with the conflict dynamic and static performance, follow-setting and disturbance-rejecting, robustness and control performance are the topic of many researchers and producers. To solve this problem, people put forward many theories and improve techniques. A lot of PID parameter tuning methods come up all the time.
The PID parameter tuning of non-linear control system is set as the engineering background. The aim is the optimal design of PID parameter. On the basis of the design and research of the advanced PID parameter tuning, the mathematical model-transfer function
is developed through correlation analysis on statistical method.
And with the optimization algorithm under constraint condition, the non-linear, Isqnonlin is set as object function. Then with connection of the non-linear constrain optimization algorithm and simulink technique, a set of adjust parameters which fit the performance index of the control system are found. And optimization design process and steps are provided. A simulation experiment of the robustness for second-order model and third-order model is made by combining example. Using the optimization design method enables non-linear system to not only meet the needs for performance index, possess a good control specific property but also have strong robustness.
In the end, the following direction of research and improvement is put forward on the base of the realization for simulation system.
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