近年來，電壓源轉換器已在工業及再生能源應用上廣泛發展，包含不斷電供應器、主動濾波器、風力發電機、太陽能電源供應站等。目前二階轉換器及中性點鉗位轉換器為工業上主流的電壓源轉換器。根據客戶的需求，兩種電路能各別被操作成背對背結構、並聯架構、三線或四線電路結構等各種應用。雖然它們在工業上有高度的操作彈性，但依舊在應用上造成許多的問題如環流、共模干擾、中性點電位振盪、控制延遲等。為了拓展轉換器於工業應用上的潛力，這些問題必須適當被探討和解決。

針對不同議題，解決方式能被分為調變技術與控制技術。調變技術藉由重新排列空間向量去解決議題如共模干擾、中性點振盪、漏電流等。另一方面，控制技術利用演算法去處理回授訊號來實現波型的補償，如環流、諧波與控制延遲等。在這篇論文中，兩種方式各自被用來改善不同工業議題。不同議題和解決方式將於每一章節被提出並詳細討論，實驗結果將驗證分析結果及提出的方法。

In recent years, voltage source converters have been widely developed in industries, including uninterrupted power supplies, active power filters, and so on. Two-level converters and neutral point clamped converters are the mainstream circuits of voltage source converters, and the types of converters, like back-to-back structures, parallel-connected structures, three-wire structures, and four-wire structures, are used to meet various demands of customers. Nevertheless, the issues, like circulating currents, common-mode interferences, neutral point oscillations, leakage currents, control delays, must be adequately addressed to take full advantage of these applications.

For industry issues, the solutions are classified as modulation techniques and control techniques. The modulation techniques are often used to address the issues, like common-mode interferences, neutral point oscillations, leakage currents, by rearranging the space vectors. The control techniques process the feedback signals with the corresponding control algorithms to compensate for the problems, like circulating currents, harmonics, and control delays. In this dissertation, both techniques are respectively used to improve different industry issues, and laboratory test results are presented to validate their effectiveness.

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
LIST OF ABBREVIATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Dissertation Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Circulating Current Issue of Parallel-connected Four-leg Inverters . . . . . . . . . 4
2.2 Common-mode Issue of Three-wire Neutral Point Clamped Converter . . . . . . . 4
2.3 Neutral Point Oscillation Issue of Four-wire Neutral Point Clamped Converter . . . 5
2.4 Leakage Current Issue of Back-to-back Neutral Point Clamped Converter . . . . . 6
2.5 Asynchronous Issue of Back-to-back Neutral Point Clamped Converter . . . . . . 6
2.6 Forced Commutation Mechanism of Back-to-back Converter . . . . . . . . . . . . 7
2.7 Issue of Active Power Filter with a Low Sampling Frequency Inverter . . . . . . . 7
2.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Modulation Techniques for Suppressing Circulating Current among Parallel-connected
Four-leg Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Analysis of Circulating Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Circulating Current of 3-D PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3.1 Effect of Injected Offset on Circulating Current . . . . . . . . . . . . . . . 14
3.3.2 3-D Active Zero State PWM . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.3 3-D Near State PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
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3.3.4 Evaluation of 3-D PWM Schemes for Circulating Current . . . . . . . . . 21
3.4 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4.1 Equal DC Bus Voltages between FLIs . . . . . . . . . . . . . . . . . . . . 22
3.4.2 Unequal DC Bus Voltages between FLIs . . . . . . . . . . . . . . . . . . . 29
3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 Modulation Techniques for Common-mode Voltage Reduction of Neutral Point
Clamped Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2 CMV of NPC Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3 Conventional PWM Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.1 Phase Deposition PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.2 Discontinuous PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.3.3 Phase Opposition Deposition PWM . . . . . . . . . . . . . . . . . . . . . 37
4.3.4 Common-mode Elimination PWM . . . . . . . . . . . . . . . . . . . . . . 38
4.4 Zero Redundant State PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.5 Compensation for Neutral Point Deviation . . . . . . . . . . . . . . . . . . . . . . 41
4.6 Evaluation between PWM Schemes . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.6.1 Waveform Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.6.2 Dynamics of Neutral Point Deviation Compensation . . . . . . . . . . . . 45
4.7 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5 Modulation Techniques for Eliminating Neutral Point Oscillation of Four-wire
NPC Active Power Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2 Modelling of Neutral Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.3 Modulation Technique of NPC Inverter . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.1 Unipolar Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3.2 Dipolar Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.4 Neutral Point Oscillation Reduction of FLNPC Inverter . . . . . . . . . . . . . . . 62
5.4.1 3-D Neutral Point Oscillation Elimination PWM . . . . . . . . . . . . . . 62
5.4.2 Offset-injection Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.5 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.5.1 Linear and Unbalanced Loads . . . . . . . . . . . . . . . . . . . . . . . . 67
5.5.2 Non-linear and Unbalanced Loads . . . . . . . . . . . . . . . . . . . . . . 67
5.6 Discussion for Effectiveness of Reducing Neutral Point Oscillation . . . . . . . . . 71
5.6.1 Neutral Point Oscillation . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
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5.6.2 Loss Analysis of Switching Devices . . . . . . . . . . . . . . . . . . . . . 75
5.6.3 Lifetime Estimation of DC-link Capacitors . . . . . . . . . . . . . . . . . 75
5.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6 Modulation Technique for Suppressing Leakage Current in BTBNPC Converter . . 81
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.2 Modelling of leakage Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.3 Displaced Pattern Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.4 Distributed Edge-aligned PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.5 Centralized Edge-aligned PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.5.1 Case I. N = N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.5.2 Case II. N 6= N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.6 Hybrid Edge-aligned PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.6.1 Switching Numbers of PWM Schemes . . . . . . . . . . . . . . . . . . . . 89
6.6.2 Modulation Range and Neutral Point Compensation . . . . . . . . . . . . 89
6.6.3 Hybrid Control Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.7 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
6.7.1 CMV Outputs of DEAPWM and CEAPWM . . . . . . . . . . . . . . . . 91
6.7.2 Effect of PF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.7.3 Asynchronous Frequency between Input and Output Ends . . . . . . . . . 91
6.7.4 Neutral Point Deviation Compensation . . . . . . . . . . . . . . . . . . . 97
6.7.5 Operation with Hybrid EAPWM . . . . . . . . . . . . . . . . . . . . . . . 97
6.8 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.8.1 Harmonic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.8.2 Thermal Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7 Control Technique for BTBNPC Converter in Asynchronous Operation . . . . . . . 108
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
7.2 Relationship between Zero-sequence Offset and Leakage Current . . . . . . . . . . 109
7.3 Operation Principle of CZSPWM Scheme . . . . . . . . . . . . . . . . . . . . . . 110
7.3.1 Extension of Modulation Range . . . . . . . . . . . . . . . . . . . . . . . 110
7.3.2 Neutral Point Potential Balance . . . . . . . . . . . . . . . . . . . . . . . 111
7.4 Asynchronism Issue in BTBNPC Converter . . . . . . . . . . . . . . . . . . . . . 111
7.4.1 Linear Modulation Range . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7.4.2 Neutral Point Compensation Capability . . . . . . . . . . . . . . . . . . . 114
7.5 Improvement for Asynchronous Issue . . . . . . . . . . . . . . . . . . . . . . . . 115
7.5.1 Discussion of Control Degrees of Freedom . . . . . . . . . . . . . . . . . 115
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7.5.2 Weighting Control of DC Bus Voltage . . . . . . . . . . . . . . . . . . . . 118
7.5.3 Discussion of Weighting Gain . . . . . . . . . . . . . . . . . . . . . . . . 120
7.6 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.6.1 Relationship between PWM Schemes and Leakage Current . . . . . . . . . 121
7.6.2 Effect of  on Modulation Range . . . . . . . . . . . . . . . . . . . . . . 123
7.6.3 Weighting Control of DC Bus Voltage . . . . . . . . . . . . . . . . . . . . 123
7.6.4 Relationship between  and Neutral Point Compensation . . . . . . . . . . 126
7.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8 Control Technique for Forced-commutating Solid-state Transfer Switch in UPS
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.2 Transfer Process of Thyristor-based STS System . . . . . . . . . . . . . . . . . . 135
8.3 Eco-mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
8.3.1 Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
8.3.2 Fault Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
8.4 Proposed Forced Commutation Mechanism . . . . . . . . . . . . . . . . . . . . . 140
8.4.1 Forced Commutation Control of Inverter . . . . . . . . . . . . . . . . . . 140
8.4.2 Forced Commutation Control of Rectifier . . . . . . . . . . . . . . . . . . 144
8.4.3 Current Detection of STS System . . . . . . . . . . . . . . . . . . . . . . 146
8.5 Double-conversion Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
8.6 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
8.6.1 Single-line to Neutral Grid Sag . . . . . . . . . . . . . . . . . . . . . . . . 149
8.6.2 Double-line to Neutral Grid Sag . . . . . . . . . . . . . . . . . . . . . . . 153
8.6.3 Double-line to Neutral Grid Swell . . . . . . . . . . . . . . . . . . . . . . 153
8.7 Discussion of Grid Frequency Issue . . . . . . . . . . . . . . . . . . . . . . . . . 157
8.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
9 Control Technique for Active Power Filtering with a Low Sampling Frequency
Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
9.1 Modelling of APF Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.2 Sampling Delay and Deadbeat Control . . . . . . . . . . . . . . . . . . . . . . . . 163
9.2.1 Discrete-time Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.2.2 Analysis of Frequency Response . . . . . . . . . . . . . . . . . . . . . . . 166
9.2.3 Discussion for Relationship between Sampling Frequency and Compensation
Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
9.3 Discussion for Relationship between CT Probe and Signal-line Impedance . . . . . 170
9.3.1 Modelling of CT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
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9.3.2 Design of CT Compensator . . . . . . . . . . . . . . . . . . . . . . . . . 172
9.4 Control Block Diagram of APF Inverter . . . . . . . . . . . . . . . . . . . . . . . 174
9.5 Laboratory Test Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
9.5.1 CT Measurement with Rsl = 0
. . . . . . . . . . . . . . . . . . . . . . 177
9.5.2 CT Measurement with Rsl = 10
. . . . . . . . . . . . . . . . . . . . . 177
9.5.3 Effect of Different Sampling Frequencies on APF . . . . . . . . . . . . . . 180
9.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
10 Conclusion and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

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