Abstract
The voltage on the power system may be subject to variations caused
by faults and sudden load fluctuations. Given the occurrence of these phenomena, the connected devices at different system levels may malfunction or even fail, thus causing economic damage and possibly compromise the overall safety and stability of the system. The Static Synchronous Compensator (STATCOM), a shunt connected, power electronic based device, was developed to mitigate the voltage sag effects. The STATCOM regulates the voltage at the point of common coupling(PCC) by providing reactive power injection.
This thesis focuses on the design and implementation of a STATCOM for unbalanced voltage sags mitigation in a weak grid. A detailed study of the voltage sag problem and its solutions has been conducted. Subsequently, a description of the synchronous reference frame (SRF) theory used in the design of a double loop vector controller, incorporating a voltage controller (outer loop), and a current controller (inner loop) is presented. A further extension of this aproach is conducted for the development of an enhanced double-decoupled synchronous reference frame (DDSRF) controller, which allows an effective regulation of both, positive- and negative sequence components of the voltage at the PCC.

The proposed control strategy has been validated through PSCAD simulations, and implemented as a laboratory-scale STATCOM system providing a 2KVA power compensation to a three-phase 220V AC voltage with a fundamental frequency of 60 Hz. This system has been tested to mitigate both balanced and unbalanced voltage sags under various load conditions.

中文摘要

在電力系統中，電壓很容易被故障以及負載的突然變化所影響。
因為這些現象的發生，在不同系統層次的連接設備可能會有故障甚
至損壞的狀況發生而造成經濟上的損失，並可能危及系統的整體安
全性和穩定性。靜止同步補償器（STATCOM）是一個用並聯方式來
減輕電壓驟降影響的電力電子設備。STATCOM可以提供虛功注入來
調節共同耦合點(PCC)上的電壓。
本研究著重於弱電網不平衡電壓驟降下的STATCOM設計與實
作。之前對於電壓驟降問題解決方法的詳細研究已經被發表，隨後
一個用同步參考框(SRF)理論用於設計外迴圈為電壓控制器，內迴圈
為電流控制器的雙迴圈向量控制器就被提出。這種方法進一步地增
強雙重解耦同步參考框(DDSRF)控制器，可以更有效的調節在PCC上
電壓的正負序成分。
此控制策略已經用PSCAD模擬程式驗證，並且用實驗室的STATCOM
，提供2KVA功率補償到三相220V交流電壓、基頻為60Hz的電
網。該系統已通過減輕在各種負載條件下平衡與不平衡電壓驟降的
測試。

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