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Novel OLTC and Local Reactive Power Inverter Control Techniques for Distribution Systems with High Penetration of Distributed Generations

배전계통내 분산전원 도입 증가에 따른 신에너지 환경에서의 새로운 OLTC 및 지역적 무효전력 인버터 제어 기법에 관한 연구

  • Chong Suk Song (송종석, 대학원 전기전자전파공학과 전자전기컴퓨터공학전공)

초록/요약

The increase in the share of renewable energy sources in the grid result in several issues, such as frequent tap changing of the on-load tap-changer (OLTC) and voltage violations to name a few. Since these renewable sources generally have intermittent characteristics, operation in compliance with the system constraints is not feasible since the existing operation methodologies are not suited for high penetration of renewable energy, thereby requiring a new operation paradigm for addressing this issue while maximizing the utilization of the existing facilities. In this dissertation, a voltage regulation technique for distribution systems with high penetration of distributed generations (DGs) is introduced so that the voltage related issues due to these DGs are resolved while maximizing the penetration in the system through a novel double-dead-band OLTC control algorithm and a local reactive support algorithm. Firstly, the novel double-dead-band algorithm is proposed to optimize the functionality of the OLTC control where the control scheme effectively uses the proposed double-dead-band concept to modify the existing line drop compensation (LDC) method so as to minimize the impact of these sources on the tap switching mechanism while preserving the original voltage regulation role. Secondly, a local reactive power support control algorithm is introduced where the PV inverter characteristics are manipulated to minimize the voltage fluctuation due to the DG active power fluctuations as well as provide a means to increase the penetration of DGs in the distribution system while not requiring any coordination with the existing voltage regulation devices. To verify the effectiveness of the proposed voltage regulation system, a 4-feeder test distribution system is used to justify the voltage regulation scheme that uses the novel OLTC control method and the local reactive power support technique to effectively regulate and maintain the system voltage within the prescribed limits while improving the entire system voltage profile. The results are compared with those of the existing voltage regulation operation schemes to verify the improvements in the voltage profile and the effectiveness of the proposed voltage regulation technique.

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초록/요약

신재생에너지원의 관심 증대에 따라 전력계통에 차지하는 비중이 커짐에 따라 탭 절환기(On-load-tap changer)의 빈번한 탭 동작 및 규정 전압 위반 등 전압 관련하여 여러 가지의 문제점을 야기한다. 이러한 신재생에너지원은 일반적으로 간헐적인 특성을 가지고 있어 기존 시스템에 설계되어 운전되고 있는 운영 방식과 적합하지 않으며 종래의 계통 운영 방식과 제약 조건을 준수하여 운영하는데 어려움이 따르기 때문에 신재생에너지원 연계에 의한 문제점들을 해결하기 위하여 기존의 설비를 최대한 활용하는 새로운 계통 운영 패러다임이 요구된다. 따라서 본 논문에서는 분산전원이 차지하는 비중이 높은 배전계통에 대한 전압 조정 기법을 제안하고자 하며 논문에서 제안한 새로운 이중 불감대 탭 절환기 제어 알고리즘과 로컬 무효전력 제어 알고리즘을 통하여 전압 관련 문제 및 분산전원 수용률 향상을 이루고자 한다. 우선, 논문에서는 탭 절환기의 기능을 최적화하기 위하여 새로운 이중 불감대 탭 절환기 알고리즘을 제안하여 기존 line drop compensation(LDC)을 기반한 제어 기법을 보완하여 본래 전압 조정 역하을 유지하면서 이러한 분산전원에 의한 탭 절환 메커니즘의 영향을 최소화하는데 목적이 있다. 둘째로는, 기존 전압 조정 장치와의 협조 제어가 필요하지 않은 전압 조정 기법으로써 태양광 인버터 특성을 활용하여 분산전원의 유효전력 변동에 의한 전압 변동을 최소화하는 등 분산전원의 수용률을 향상하는 수단을 제공하는 로컬 무효 전력 제어 알고리즘이 제안되고 있다. 본 논문에서 제안되는 전압 조정 기법의 효과를 검증하기 위해 4개 피더 테스트 배전계통을 적용하였고 새로운 탭 절환기과 로컬 무효전력 전압 조정 기법을 통한 효과적인 전압 제어, 계통 규정 전압 유지 및 전체 계통의 전압 프로필에 대한 개선 효과를 기존 전압 조정 기법들과 비교분석을 통하여 검증하였다.

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목차

ABSTRACT I
TABLE OF CONTENTS III
LIST OF TABLES VI
LIST OF FIGURES VII

CHAPTER 1. INTRODUCTIONS 1
1.1 Motivation and Objectives 1
1.2 Literature Review 3
1.3 Scientific Contributions 7
1.4 Outline of Dissertation 8

CHAPTER 2. VOLTAGE REGULATION AND DISTRIBUTED GENERATION 10
2.1 Impact of Distributed Generation on the Distribution System 10
2.2 Voltage Regulation in Distributed Systems 11
2.3 Techniques of Voltage Regulation and Reactive Compensation 13
2.3.1 Step Voltage Regulator 13
2.3.2 Synchronous Generators 15
2.3.3 Capacitor Banks 16
2.3.4 Inverter Control 17
2.4 Previous and Ongoing Studies on Reactive Power Compensation Using PV Inverters 19
2.4.1 Autonomous VAR Modes (Local Control Modes) 22

CHAPTER 3. NOVEL OLTC VOLTAGE REGULATION SCHEME FOR HIGH PENETRATION OF DISTRIBUTED GENERATION 26
3.1 Control Mechanism of OLTC Transformer 26
3.1.1 Line Drop Compensation Method 30
3.2 Novel On-Load-Tap-Changer Algorithm 32
3.2.1 Double Dead-Band Algorithm 33
3.2.2 Double-Dead-Band Parameter Selection 35
3.2.3 Novel OLTC Control Algorithm 39

CHAPTER 4. LOCAL REACTIVE POWER SUPPORT ALGORITHM USING INVERTER-BASED DISTRIBUTED GENERATIONS 43
4.1 Local Reactive Power Support Algorithm 43
4.1.1 Derivation of Maximum Penetration of DGs in the Feeder System 44
4.1.2 Voltage Sensitivity Analysis 47
4.2 Reactive Power Support Formulation 52

CHAPTER 5. CASE STUDIES 59
5.1 Introduction of Test Cases 59
5.2 Novel OLTC Double-Dead-Band Algorithm Case Studies 61
5.2.1 Case I: Comparative Study by changing Double-Dead-Band Parameter 62
5.2.2 Case II: Comparative Study between Conventional LDC and Proposed Technique 64
5.2.3 Case III: Comparative Study for Load Restoration Condition 71
5.3 Reactive Power Support Algorithm Case Studies 73
5.3.1 Case II: Verification of the Local Reactive Power Support Algorithm 74
5.3.2 Case II: Comparative Study between Local Reactive Power Support Algorithm and without any Reactive Support 77
5.3.3 Case III: Comparative Studyof the Local Reactive Power Support Algorithm with other Reactive Power Support Techniques 78
5.4 Discussions 79

CHAPTER 6. CONCLUSIONS 82

REFERENCES 84
APPENDIX A : SYSTEM DATA OF TEST DISTRIBUTION SYSTEM 92
APPENDIX B : PQ VOLTAGE SENSITIVITY PROFILE 94
APPENDIX C : LOCAL REACTIVE POWER SUPPORT ALGORITHM CASE STUDIES 96
KOREAN ABSTRACT 108


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