학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 8. 설승기. ; Control methods of the Modular Multilevel Converter (MMC) are classified into indirect modulation based control and direct modulation based control. In this thesis, a modified modeling of an indirect modulated MMC is proposed for generalized DC bus of High Voltage DC (HVDC) transmission. Based on the proposed modeling, a comprehensive arm capacitor energy control strategy is derived, which is valid regardless of the characteristics of the DC bus. In addition, for the direct modulated MMC, mechanism and dynamics of the natural balancing of the arm capacitor energy are analyzed. It is proven mathematically in this thesis that arm capacitor energy of six arms of the MMC converges to be balanced inherently regardless of the characteristics of the DC bus while an MMC is direct modulated. A novel control strategy of the MMC based Voltage Source Converter (VSC)-HVDC transmission system is also proposed. Different from the conventional two-level converter based transmission system or the direct modulated MMC based transmission system, the instantaneous DC bus voltage of the MMC is fully decoupled from the energy stored in the DC capacitors of the converter by the proposed method. The transmission line voltage fluctuation is also suppressed during power flow variation by the proposed method. Validity of the conducted work in this thesis is verified by both computer simulations and experiments. ; Contents Abstract i Contents iii 1. Introduction 1 1.1 Background 1 1.1.1. The Era of Mercury Arc Valves 2 1.1.2. The Era of Power Semiconductor Valves 3 1.2 Review of VSC-HVDC Transmission 3 1.3 MMC, a New Era of VSC-HVDC Technology 6 1.4 Purpose of This Thesis 9 1.5 Thesis Outline 11 2. Basic Principle and Control of the MMC 12 2.1. Operation Principle of the MMC 12 2.2. Indirect Modulation and Direct Modulation 13 2.3. Review of the Research on Control of the MMC 15 3. Indirect Modulation Based Control Strategy of MMC 18 3.1 Modeling of the Indirect Modulated MMC with Stiff Voltage Sourced DC Bus 20 3.2 Control of the Indirect Modulated MMC with Stiff Voltage Sourced DC Bus 24 3.2.1 Current Control of the Indirect Modulated MMC with Stiff Voltage Sourced DC Bus 24 3.2.2 Arm Capacitor Energy Control of the Indirect Modulated MMC with Stiff Voltage Sourced DC Bus 25 3.3 Modeling of the Indirect Modulated MMC with Generalized DC Bus 29 3.3.1 Analysis of AC Grid Current of the MMC with Generalized DC Bus 31 3.3.2 Analysis of DC Bus Current of the MMC with Generalized DC Bus 34 3.3.3 Analysis of Circulating Current of the MMC with Generalized DC Bus 36 3.4 Control of the Indirect Modulated MMC with Generalized DC Bus 40 3.4.1 Control of Energy Stored in the Whole Cell Capacitors of the MMC 42 3.4.2 Balancing of Three Phase Leg Capacitor Energy 44 3.4.3 Balancing of Upper and Lower Arm Capacitor Energy 47 3.4.3 Overall Structure of the Proposed Method and Practical Implementation Issues 54 3.5 Ride Through Strategy of the AC Grid Single Line to Ground (SLG) Short Circuit Fault 56 4. Direct Modulation Based Control Strategy of the MMC 64 4.1 Modeling of the Direct Modulated MMC with Stiff Voltage Sourced DC Bus 65 4.1.1 Arm Output Voltage and Insertion Ratio 65 4.1.2 Analysis of Grid Current and Leg Current 67 4.2 Mechanism and Dynamics of Arm Capacitor Energy Regulation of the MMC with Stiff Voltage Sourced DC Bus 70 4.2.1 Dynamics of Sum of Upper and Lower Arm Capacitor Voltages 71 4.2.2 Dynamics of Difference of Upper and Lower Arm Capacitor Voltages 73 4.3 Modeling of the Direct Modulated MMC with Generalized DC Bus 74 4.4 Mechanism and Dynamics of Arm Capacitor Energy Balancing of the MMC with Generalized DC Bus 77 4.4.1 Dynamics of Balancing of Leg Capacitor Voltages 77 4.4.2 Dynamics of Differences of Upper and Lower Arm Capacitor Voltages 79 5. Control of an MMC Based Point-to-Point HVDC Transmission System 85 5.1 Direct Modulation Based Control Strategy of the Point-to-Point HVDC Transmission System 85 5.2 Indirect Modulation Based Control Strategy of Point-to-Point HVDC Transmission System 88 5.2.1 Proposed Voltage-Voltage (VV) Control Strategy of VSC-HVDC Transmission System Based on Indirect Modulated MMC 88 5.2.2 Proposed Voltage-Power (VP) Control Strategy of VSC-HVDC Transmission System Based on Indirect Modulated MMC 89 6. Simulations and Experimental Verification 91 6.1 Simulation of an MMC under Indirect Modulation Based Control Strategy 91 6.1.1 Simulation of a 217 Level, ±200kV MMC in No Load Condition 91 6.1.2 Simulation of a 217 Level, ±200kV MMC in Loaded Condition 97 6.2 Experimental Verification of an MMC under Indirect Modulation Based Control Strategy 101 6.2.1 Experimental Verification of a 7-Level, 300V MMC in No Load Condition 102 6.2.2 Experimental Verification of a 7-Level, 300V MMC in Loaded Condition 107 6.3 Simulation of an MMC during an AC Grid SLG Fault 110 6.4 Simulation of an MMC under Direct Modulation Based Control Strategy 113 6.5 Simulation of a Point-to-Point HVDC Transmission System under Direct Modulation Based Control Strategy 117 6.6 Simulation of a Point-to-Point HVDC Transmission System under Indirect Modulation Based Control Strategy 119 6.6.1 Simulation of a HVDC System Employing VV Control 120 6.6.2 Simulation of a HVDC System Employing VP Control 122 6.6.3 Simulation of a HVDC System Employing VP Control to Feed a Passive Grid 124 6.7 Experimental Verification of a Point-to-Point HVDC Transmission System under Indirect Modulation Based Control Strategy 126 6.7.1 Experiment of a HVDC System Employing Proposed VV Control 127 6.7.2 Experiment of a HVDC System Employing Proposed VP Control 131 7. Conclusions 134 7.1 Conclusions 134 7.2 Contributions 136 7.3 Future Work 136 Bibliography 138 APPENDIX A 140 APPENDIX B 141 APPENDIX C 142 APPENDIX D 143 APPENDIX E 144 APPENDIX F 145 ; Master


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    Titel :

    Modeling and Control of Modular Multilevel Voltage Source Converters for HVDC Application with Generalized DC Bus



    Erscheinungsdatum :

    2014-01-01


    Medientyp :

    Hochschulschrift


    Format :

    Elektronische Ressource


    Sprache :

    Englisch



    Klassifikation :

    DDC:    629




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