本篇論文提出一個微電網中下降型控制逆變器之虛擬電感設計。下降型控制逆變器可以在微電網孤島運轉時維持電壓與頻率，於微電網併網時啟動虛擬電感，無需事先進行與市電之同步，即可完成與市電之併網。虛擬電感被設計於併網瞬間使用較大初始電感值以抑制非同步併網所造成的暫態電流，並且電感會動態地隨著時間衰減，經過一段特定的時間之後降至最終電感值。考慮到動態虛擬電感為時變函數，並不適合使用拉普拉斯轉換運算作分析，故使用狀態空間模型與小訊號分析建立出線性時變小訊號系統模型，界定動態虛擬電感對系統穩定度之影響。系統之建模包含下降控制器、電壓控制器、輸出濾波器、輸出線阻抗與動態虛擬電感。本文會詳細說明動態虛擬電感設計，提出三個關鍵參數的設計準則：初始電感值、最終電感值與時間常數。最後使用模擬軟體建構一簡化之微電網模型，驗證虛擬電感可以幫助下降型控制逆變器非同步併聯微電網以及達成微電網非同步併網之操作，並且於實驗設置一下降型控制逆變器使用不同類型虛擬阻抗併網，比較實驗結果與討論。

This paper presents a design of virtual inductance for droop-controlled inverter in microgrid. This droop-controlled inverter can regulate voltage magnitude and frequency when microgrid is operated in islanded mode. Moreover, by applying the virtual inductance, microgrid is able to connect to grid without pre-synchronization. The virtual inductance is designed with a large initial value that will dynamically decrease over time. After a specific time period, the virtual inductance reaches steady state and is fixed at a final value. Because the dynamic virtual inductance is time-varying, Laplace transform operation is not suitable for analysis. Instead, state-space model and small-signal analysis is preferred to conduct the system model and determine the system stability. The system model includes the droop control, the voltage control, the output filter, the output line impedance and the dynamic virtual inductance. The design consideration of the virtual inductance will be explained specifically; the corresponding design criterion of initial value, final value and time constant will be described in detail, too. Time-domain simulation with respect to a simplified microgrid was built to verify that non-synchronous grid-connected operation can be achieved by using the well-design virtual inductance. Furthermore, a laboratory prototype with a droop-controlled inverter was set up to compare the performance between different types of virtual impedance.

Catalogue
論文審定書 i
摘要 ii
Abstract iii
Catalogue iv
Figure of Contents vii
Table of Contents xi
Chapter 1. Introduction 1
Chapter 2. Literature review 5
2.1 Power flow analysis and droop control 5
2.2 Phase-locked loop and frame transformation 10
2.3 Output filter 13
2.4 Voltage and current control strategy 15
2.5 Synchronization of grid connection 16
2.6 Non-synchronous grid connection technique 18
2.7 Applications of virtual impedance 22
Chapter 3. Design Consideration of Virtual Inductance 25
3.1 Design of droop control and multi-loop voltage control 25
3.1.1 The determination of droop controller 29
3.1.2 The determination of multi-loop controller 31
3.2 Design and analysis of the virtual inductance loop 33
3.2.1 The modeling of the droop controller 36
3.2.2 The modeling of the voltage controller 38
3.2.3 The modeling of the output filter and line impedance 40
3.2.4 The modeling of overall system 41
3.2.5 The determination of virtual inductance 44
3.2.6 Modeling extension for multiple inverters in Microgrid 46
3.2.7 Further consideration without synchronization technique 48
Chapter 4. Time Domain Simulation 51
4.1 Different types of virtual inductance 51
4.2 Multiple droop-controlled inverters in microgrid 55
Chapter 5. Experiments 72
5.1 The ride-through technique considering no virtual impedance 76
5.2 The ride-through technique considering the virtual inductance 78
5.2.1 The exponential decreasing virtual inductance 78
5.2.2 The constant virtual inductance 85
5.3 The ride-through technique considering virtual resistance 87
5.3.1 The exponential decreasing virtual resistance 87
5.3.2 The constant virtual resistance 91
5.4 Summary 93
Chapter 6. Conclusion 94
Reference 96

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