RST數位控制器為雙自由度控制器，其中數位濾波器R和S的設計是為了提供負載擾動排除所需的控制器調節輸出，而數位濾波器T的設計是為了達成特定的設定點追蹤特性，換言之，RST結構可同時滿足負載擾動排除和設定點追蹤的不同性能要求。本論文針對RST數位控制器提出一個改良式極點配置設計方法，在指定的強韌性限制下（增益邊限、相位邊限和最大高頻增益），藉由調整三個閉迴路參數，即可得到針對負載擾動排除的最小誤差和之性能指標，然後藉由調整一個迴路外參數以達成滿意的設定點追蹤響應。相較於現有的設計方法而言，本設計法能夠在相同強韌性下獲得最佳的性能指標，亦能更好地處理包含時延、過阻尼及低阻尼、穩定及不穩定零點、積分器及不穩定極點之多種程序動態。
本論文亦比較閉迴路和開迴路鑑別模型對控制器設計的影響。當模型結構未知時，發現閉迴路鑑別所得模型可以更精確地描述真實受控體的動態行為，因此其模型可設計出較佳性能的控制器。

RST digital controller are two-degrees-of-freedom controllers. The digital filters R and S are designed to provide the desired regulation of controller output for load disturbance rejection, while the digital filter T is designed to achieve the specified performance of set-point tracking. In other words, the RST structure can satisfy simultaneously the distinct requirements on load disturbance rejection and set-point tracking. This thesis presents an improved design method of pole placement for RST digital controllers. Under the specified constraints on robustness (gain margin, phase margin, and maximum gain for high frequencies), the method can give rise to the minimum error sum performance criterion for load disturbance rejection by adjusting three closed-loop tuning parameters. Then the satisfactory response of set-point tracking can be achieved by adjusting another tuning parameter outside the closed loop. Compared with available methods, the design method can obtain the best performance under the same robustness constraints. Besides, it can better deal with a wide variety of process dynamics including time delays, overdamped and underdamped behaviors, stable and unstable zeros, and integrators and unstable poles.
This thesis also compares the influence of closed-loop and open-loop identification models on controller design. When the model structure is unknown, it is found that the model identified in closed loop can describe the dynamic behavior of the actual plant more precisely, and hence give rise to a controller design with better performance.

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