基于闭环耦合度的大系统常规PID控制回路的投用规则

PID Control Loop Putting-in-service Rules for Large System Based on Closed-loop Coupling Degree

化工过程全流程为具有高维输入输出的多变量大系统,内部存在一定程度的耦合作用,因此其底层常规PID控制系统的设计、投用和整定也必然与整个系统的耦合程度有关。首先,提出了闭环相对增益和耦合度的概念,分析闭环相对增益在理想控制条件下与开环相对增益的等效性,发现闭环控制回路的反馈作用引起操纵变量和被控变量的关联,由此加剧整个系统的耦合程度,因此闭环控制回路并非投用得越多越好。然后,提出了基于闭环耦合度的化工过程大系统常规PID控制回路的投用规则,根据被控过程开环相对增益阵确定控制回路变量配对和投用顺序,依次投用各控制回路并计算控制回路的耦合度,当耦合度超过阈值时停止剩余控制回路的投用。最后,以典型多变量TE过程为例验证了该投用规则的有效性。

Considering the fact that chemical plant-wide process is a multivariable large-scale system with high-dimensional inputs and outputs and certain internal interaction exists there;the design, putting-inservice and setting of the underlying PID control system involves the degree of coupling of the whole system.Firstly, the concept of closed-loop relative gain and coupling degree was put forward to analyze equivalence of the closed-loop relative gain under ideal control. The results show that, the feedback of closed control loop can cause the interaction between controlled variable and manipulated variable and aggravate the coupling degree of the whole system, and it is not better that more PID control loops are put into service. Secondly, the sequential putting-in-service rules of PID control loops were proposed based on closed-loop coupling degree for large-scale chemical process, including having the open-loop relative gain array of controlled process based to determine variable pairing and putting-in-service sequence of PID control loops and having each PID control loop put into service in sequence and the coupling degree calculated for each PID control loop. When the coupling degree exceeds the threshold value, the remaining PID control loops will be suspended. Finally, a typical multivariable large-scale system(Tennessee Eastman process) was taken as an example to verify the putting-in-service rules’ effectiveness of the PID control loop.