台灣的配電系統由於三相負載分配的不平衡以及採用兩個單相變壓器繞組的U-V連接或V-V連接供電至負載等因素，導致配電系統三相電壓的不平衡，進而使中性線電流增加導致接地電驛可能跳脫，而三相不平衡的供電也會造成額外的線路損失及降低交流馬達的運轉效率，因此本論文提出採用多階靜態同步補償器來改善配電系統三相電壓不平衡的特性。本論文之系統架構一係以IEEE四節點之測試饋線，利用多階靜態同步補償器改善系統之電壓不平衡，並與一般配電型靜態同步補償器之效能做比較；本論文之系統架構二係以IEEE十三匯流排系統，利用多階靜態同步補償器改善系統之電壓不平衡，並觀察對系統中再生能源所造成的影響。本論文由模擬結果驗證多階靜態同步補償器於改善配電系統三相電壓不平衡的可行性。

Three-phase voltage unbalance of distribution systems due to unequal loading on three phases and the U-V or V-V winding connection of two single-phase distribution transformers occurs in most utility companies including Taiwan Power Company. Three-phase voltage unbalance can lead to sudden trip of ground relay, extra power losses of distribution lines, efficiency reduction of induction motors, etc. This thesis proposes a multilevel static synchronous compensator (ML-STATCOM) to mitigate three-phase voltage unbalance problems in distribution systems. System configuration 1 of this thesis is based on the IEEE 4-node test feeder with three-phase voltage unbalance while the ML-STATCOM is proposed to improve the system voltage unbalance and compare the effectiveness of a distribution STATCOM (D-STATCOM). System configuration 2 of this thesis is based on the IEEE 13-bus feeder with unequal loading on three phases and the U-V or V-V winding connection of two single-phase distribution transformers while the ML-STATCOM is proposed to reduce three-phase voltage unbalance and the power fluctuations caused by PV/wind renewables in the system. The simulation results show that the employment of the proposed ML-STATCOM can effectively reduce three-phase voltage unbalance of the studied distribution systems.

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