工業發展與人口增加，用電需求量大增，為提供良好供電品質與提高系統穩定度，各電力系統間遂發展為互聯系統，使傳輸距離增長，當發電廠遠離負載中心系統時負載變動或故障發生就會容易引發自發性低頻振盪。為改善系統低頻振盪，提高系統阻尼，本論文提出動態極點指定之觀念，並利用最佳降階系統模型理論，以確保輸出變數之物理性與輸出回授之有效性，接著推導出亞固有結構預設法，最後整合利用輸出回授之最佳分離式穩定器設計的新方法，並應用於設計分離式系統時變穩定器。由模擬結果顯示，系統動態極點，固有結構指定與穩定性之改善，可經由系統時變穩定器的設計達成，並符合實際應用。 In power system, the degree of low frequency oscillation and damping ratio of the system are the most important factors influencing the electro-mechanical output quality. Hence, the improvement of the damping ratio will be the index of the power system stabilizer design. The new concept of dynamic poles assignment is proposed in this thesis. The technique of optimal reduced order model is used to retain the physical meaning and effectiveness of the output state variables. Following, the theorem of Preseted Deutero-Eigenstructure Method are derived. Based on the output states feedback, a new method of designing optimal decentralized stabilizer is also introduced. The concept is used to design the time-varying stabilizer of power system. The results of applying the proposed power system stabilizer design approach to the study system show that the system stability can improved. The time-varying stabilizers introduced in this study are very simple and will be easily implemented.