Experimental Study of a Combined Global/Local Control System Robust to Model Inaccuracy for Sensitive Nonlinear Systems

一般傳統的比例－積分自適控制器，在解決非線性系統之制器問題時，通常採用調諧比例－積分控制器參數的方式；而本文，則以模式預測控制作為一個全域的控制器，而比例－積分控制器僅擔任局域控制的角色，發展出－全域－局域組合控制策略，來解決既靈敏又兼具不確定性的非線系統之控制問題。另外，在控制模式不準確的系統時，若以人工智慧類神經網路建模時，常使用模式預測控制，但是因為訓練資料不完全或其它的因素，使得模式有誤差存在，而無法達到有效的控制；而應用此諧合控制策略，則可用比例－積分來修正輔助模式預測控制的控制效果。最後，為了證明此控制理論的強健性，特別以酸鹼中和反應為驗證實驗，因為中和反應在滴定當量點附近之區域是相當敏感又非線性化的；經由多次的模擬與實驗的結果顯示，此全域－局域組合控制策略，確實能夠在高度非線性的系統有非常好的控制表現。

關鍵字

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並列摘要

Chemical processes are nonlinear. Processes with extremely high nonlinearities, such as neutralization and high-purity distillation, are very important and need special considerations. The basic problem with such nonlinear processes is that the performance of model-based control is very sensitive to model inaccuracy. It seems that robust control is impossible with pure model based control algorithms. Model predictive control (MPC) has been widely implemented in the chemical industry. However, not very many successful cases of implementing nonlinear models can be found in the literatures. In addition, when such a model is inaccurate, high-frequency oscillation appears across the sensitive region. On the other hand, an accurate model is expensive and frequently impossible since operating data in the sensitive region are scarce. The above factors lead to unacceptable control results. To solve the above problems, we propose a combined global/local control (GLC) in which, when disturbances occur, the global control (GC, MPC in this study), a nonlinear controller, steers the process under control into or near the sensitive region; then, the local control (PI in this study) takes over and finally settles the process at the desired set point. Both simulation and experimental results show that such a combination control is economical. In this study, unlike our previous research, a PI controller was implemented, because PI control can be easily tuned for the sensitive region and a model of moderate accuracy for other non-sensitive regions can be built with much less effort.

並列關鍵字

Model inaccuracy ； Global/local control ； Model predictive control ； Sensitive nonlinear system ； PI controller

國際替代計量

Experimental Study of a Combined Global/Local Control System Robust to Model Inaccuracy for Sensitive Nonlinear Systems

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