本文以數位控制器實現可操作於不平衡負載之三相四臂 T 型式換流器並聯系統。此系統使用虛擬電阻下垂控制法作為並聯運轉之控制策略，達成無通訊方式並具功率分配之功能，而加入虛擬電阻以確保各換流器輸出阻抗特性一致，有效降低輸出功率之誤差。
換流器架構採用三相四臂 T 型式拓樸架構，此架構特點為輸出電壓為多階波形，能有效降低輸出電壓諧波含量，額外加入的第四臂更可提升對於不平衡電流之控制力，輸出端使用 LCL 型濾波器，濾除開關高次諧波並有效降低輸出電壓諧波含量。針對不平衡負載，分別使用正、負、零序獨立控制方式，透過抑制負序與零序電壓，使三相輸出電壓維持平衡。在調變技術上，本文選用了 CBPWM 中的均值零序注入調變，其特點為除了擁有與 SVPWM 相同的高直流電壓利用率外，其調變波形生成容易、不需判斷空間向量區間，所以易於實現數位化的優點。本文使用電路模擬軟體 PSIM 建構出一組額定功率 8 kW，輸入直流電壓 800 V 輸出交流電壓 220 V 之三相換流器並進行模擬測試。數位控制核心選用德州儀器公司出產之 TMS320F28379D，實現系統控制並且驗證硬體設計與控制法。最終製作兩臺 8 kW 三相四臂 T 型式換流器，完成系統並聯測試與驗證。

This thesis proposed the design and implementation of a digitallycontrolled three-phase four-leg T-type inverter parallel system with the
functions of operating in unbalanced loads. To achieve the power sharing
without communication, the system used the virtual resistance droop
control method as the control strategy for parallel operation, and added
virtual resistance to ensure that the output impedance of each inverter was
the same, and reduced the error of output power effectively.
The proposed inverter topology used three-phase four-leg T-type
topology. Using this topology can have some advantages, for example, the
multi-level output voltage can reduce the output voltage THD significantly,
the additional legs can improve the control of unbalanced current. Using
LCL filter can eliminate the switching harmonics and reduce the output
voltage THD effectively. This research used positive, negative and zero
sequence control independently for unbalanced loads, and inhibited the
negative and zero sequence voltage to maintain three-phase voltage
balance. The average zero-sequence component injection of Carrier-based
PWM was adopted as the modulation method, which had the high
utilization of DC voltage as SVPWM, it also had some advantages, for
instance, it can be produced and digitized easily, and it did not need to
determine the location of the space vector. This thesis used the circuit
simulation software, which was PSIM to construct a three phase inverter
with 8 kW rated power, 220 V output AC voltage, and 800 V DC voltage
to verify the function. The digital controller, which was used in this thesis
was the TMS320F28379D from Texas Instruments to realize the system
control and the verification. Finally, this thesis implemented a pair of 8 kW
three-phase four-leg T-type inverters to verify the system feasibility.

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