串級控制系統之PID控制器設計：基於模式與直接基於數據之方法

PID Controller Design for Cascade Control Systems: Model-Based and Direct Data-Based Approaches

廖信嘉(Xin-Jia Liao)

指導教授 ： 鄭智成

國立臺北科技大學/工程學院/化學工程研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00372

摘要

串級控制是能夠提高單環路控制性能最成功的控制架構之一，這也使得串級控制被廣泛的應用在化學工業中。本研究提出串級控制基於模式法和直接基於數據法之PID控制器設計，藉由一次閉環路階梯測試就可同時完成主控制器與次控制器調諧。
在基於模式法設計PID控制器時，程序模式在一開始就被識別出來，接著兩個控制器利用內部模式控制(internal model control, IMC)方法完成調諧。在考慮串級控制基本概念下，次控制器被設計成快速排除擾動。並且在不需要額外實驗下，根據次控制器設計完成後，基於內環路的實際動態行為進行識別等效程序的模式識別，並且設計主控制器。而系統之韌性問題也在控制器調諧過程中被加入考慮，進而對IMC調諧參數的選擇制定明確的方向。
基於模式之PID控制器設計方法在高階程序的性能會下降，其原因為高階程序動態識別成低階模式時產生不可避免的建模誤差所造成。因此，在不訴諸於程序模式下，直接以基於一組程序輸入及輸出數據設計PID控制器，這是一個很吸引人的替代方法。直接基於數據的PID控制器設計中，設計的目標是要找到一組PID控制器參數，使內環路與外環路的動態行為盡可能貼近所指定的參考模式，而參考模式是參照基於模式設計方法為相同的設計目標。因此便能得到與建議的設計方法有關之最佳化問題。基於兩個可調參數的選擇提出一個明確規範，便能各自處理內環路和外環路的性能與韌性間權重問題，以達到所想要系統的韌性水平。
模擬範例證實本研究所提出兩種串級控制系統之PID設計方法的有效性。結果呈現，在基於數據法是能夠達到與基於模型法相當或是更好的控制性能。

關鍵字

串級控制；PID控制器設計 ； 基於數據調諧 ； 基於模式調諧 ； 韌性

並列摘要

Cascade control is one of the most successful control structures for enhancing single-loop control performance, which has lead to the extensive implementation of cascade control in chemical process industries. This study presents model-based and direct data-based PID controller design approaches for cascade control systems in which both primary and secondary controllers are tuned simultaneously using a single closed-loop step test.
In the model-based PID controller design, the process models are first identified, and then the two PID controllers are tuned using an internal model control (IMC) approach. Considering the rationale of cascade control, the secondary controller is designed for faster disturbance attenuation. Without requiring an additional experiment, the primary controller is designed based on an identified process model that accurately accounts for inner loop dynamics. The robustness considerations are included in the controller tuning process to develop explicit guidelines for the selection of the IMC tuning parameters.
The performance of model-based PID design methods would degrade for higher-order process dynamics owing to the inevitable modeling error. Consequently, it is an attractive alternative to design PID controllers directly based on a set of process input and output data without resorting to process models. In the direct data-based PID controller design, the design goal is to find PID parameters such that the resulting inner and outer loops behave as closely as possible to the appropriately specified reference models which are developed from model-based design. The optimization problems pertaining to the proposed design are derived. The desired levels of system robustness explicitly guide the selection of two adjustable parameters to deal with the trade-off between performance and robustness for inner and outer loops independently.
Simulation examples confirm the effectiveness of two proposed PID design approaches for cascade control systems. The results show that the data-based method is able to achieve comparable or better control performance than the model-based method.

並列關鍵字

Cascade control ； PID controller design ； Model-based tuning ； Data-based tuning ； Robustness

參考文獻

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