本研究研製高頻LCL併網型換流器，電力級為三相三線全橋架構。為了因應高頻系統，微控制器選用Renesas RX71M，具有更短的轉換時間與多個轉換頻道。併網型換流器能輸出實功與輸出特定功率因數下的電流至電網，依照電網要求將實功與虛功饋入電網。
三相三線LCL併網型換流器可廣泛應用於再生能源發電系統、馬達驅動和電動車的充電等，以往受限開關元件、濾波元件及控制方法的頻寬，換流器僅操作於低頻，導致系統體積過大。本系統提升切換頻率至 ，可降低系統體積，提高功率密度。
在控制方面，本系統採用解耦合直接數位控制法，將直流鏈電壓、開關切換頻率及電感隨電流變化考慮進去，精確地計算出下一週期的開關責任比率，並使用零序注入法，避免開關責任比率過度調變。此控制法可使三相三線系統等效成三組單相獨立系統進行控制，相較傳統的abc –dq軸轉換，可大幅減低控制法則推導計算時間，並且可以提昇控制頻寬。此外，解耦合直接數位控制搭配空間向量調變(SVPWM)，與正弦脈波寬度調變(SPWM)相比，可得到較好的直流電壓利用率。
本論文詳細介紹解耦合直接數位控制法、LCL濾波器設計流程、硬體周邊電路及實務考量。利用模擬驗證此控制法能應用於三相三線全橋系統，並實測其功能，最後進行損耗估測。
本論文主要貢獻為:(1)採用解耦合直接數位控制法，證明三相三線系統能實現單相控制。(2)設計LCL濾波器，使換流器輸出電流弦波，其總諧波失真率符合併網規範要求。

This research is aimed at designing and implementing an LCL high frequency three-phase three-wire grid-connected inverter system.For the high switching frequency system, a micro-controller Renesas RX71M is adopted because of its short conversion time and having many A/D conversion channels. The grid-connected inverter can inject active/reactive power into the grid by following the command from utility company.
A three-phase three-wire LCL grid-connected inverter has been widely utilized in renewable energy power generation systems, motor drivers, electric-vehicle chargers, etc. Restricted by switching elements, filter components, and the bandwidth of conventional control methods, inverter systems are only operated at low frequency, resulting in high volume. The proposed inverter operated at 100 kHz switching frequency, which reduces the size of the filter components and increases the power density.
Decoupled three-phase direct digital control with the division-summation (D-Σ) process is used to control the system. The DC link voltage, switching frequency and inductance variation are taken into account in the control-law derivation. Using the decoupled three-phase direct digital control with the D-Σ process can accurately determine the duty ratios of the switches for next cycle. Combining zero-sequence injection with the control laws can avoid the duty ratios from over modulation. Since the three-phase control-law expressions are decoupled, the control of a three-phase three-wire inverter can be equivalent to that of a single-phase inverter. Comparing with con¬ventional abc to dq frame transfor¬mation, the control law derivation of the direct digital control can be simplified and can improve the bandwidth of the system. Compared with the SPWM, the decoupled three-phase direct digital control with SVPWM can obtain better dc voltage utilization.
This thesis derives the decoupled three-phase direct digital control laws, designs LCL filters and hardware circuits, and describes practical considerations in detail . The feasibility of the three-phase three-wire full-bridge inverter with the decoupled three-phase direct digital control has been verified by simulated and experimental result. Finally, system efficiency is estimated in the thesis.
The major contributions of this thesis are : (1)Verify that the control of a three-phase three-wire converter can be equivalent to that of a single- phase inverter when adopting the decoupled three-phase direct digital control. (2) Design LCL filters for the inverter to achieve the output current complying with the regulation.

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