本文以數位控制實現具備援之功能的三相三階換流器並聯系統。此系統使用強健型下垂控制法，作為並聯運轉之控制策略。其優勢為無需通訊方式即可達成功率分配，相較於傳統下垂控制法有更好的響應速度、效率及更低的輸出壓降。
在換流器部分，本文採用T型式拓樸架構，此架構所使用元件數少、效率高，且能有效減少輸出電壓諧波含量。在控制部分，使用載波脈波寬度調變法，將三相參考信號注入三次諧波，相比於同樣得到大量使用之空間向量脈波寬度調變方式，擁有同樣高的電壓利用率，且有調變波形生成容易、不需判斷空間向量區間，易於實現數位化之特性，最後實際製作兩臺8 kW三相換流器，完成並聯測試，印證所提理論之可行性。

This thesis proposes the design and implementation of a digitally-controlled three-phase three level inverter parallel system with redundancy feature. This system uses the robust droop control method as the control strategy for parallel operation. The advantage is that it does not need communication between the inverters when accomplishing the correct power sharing. It has better response and efficiency than the traditional droop control.
In the part of inverter, the proposed three level circuit is using T-type topology. The benefits of this topology are using fewer components, high efficiency and the lower output voltage THD. This thesis uses a variant of Carrier-Based PWM(CBPWM) as the control scheme, inject the third harmonic into the three-phase reference signal. Compare with Space Vector PWM(SVPWM), it has the same voltage utilization rate, the modulation waveform of Carrier-Based PWM is easy to produce and there is no need to determine the location of the space vector. Finally, two 8 kW inverters are actually produced and paralleled to make sure the feasibility of the proposed theory.

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