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1、环形直流微电网线路故障分析与直流固态断路器研究 Line FaultAnalysisandStudy ofDCSolid-stateCircuit Breaker in Loop-type DC Microgrid：电气工程：直流微电网二一五年五月摘要随着全球经济的发展，能源需求快速增长，尤其是对电力的需求更加凸显，环境问题也日益严重。在能源需求和环境保护的双重压力下，分布式发电受到了广泛的关注。为了最大限度地发掘分布式发电的价值，微电网的概念应运而生。直流微电网具有控制简单、变换环节少和线路带载能力强的优势。本文基于低压环状直流微电网，对其直流线路短路故障和直流固态断路器进行分析和研究，为推
2、广直流微电网的工程应用提供技术支持。论文首先对微电网的拓扑结构、各端口组成部分和直流线路等效模型进行了阐述，基于三端低压环形直流微电网，详细地分析了线路发生最严酷短路故障时，直流母线上故障电流的特性，总结了直流微电网系统故障与保护的特殊性，基于分析结果提出了直流微电网对直流固态断路器的需求。其次，论文以电压等级为200V，容量为4kW的环网直流微电网为例，对现有直流固态断路器技术路线进行了对比分析，展开对带传统RCD缓冲电路的直流固态断路器的研究。针对充放电型、放电阻止和型RCD缓冲电路从固态断路器瞬时过电压及其达到稳态的时间、线路故障电流峰值及其能量转移的快慢和缓冲电容电流电压峰值三方面，对
3、极间短路情况下缓冲电容充电和放电过程进行了详细分析，在相同参数条件下以放电阻止型RCD缓冲电路性能最优，同时给出了缓冲电容、缓冲电阻和二极管的设计方法。仿真结果证明了理论分析的正确性和缓冲方案的可行性。最后，从带传统RCD缓冲电路的直流固态断路器的局限性出发，借鉴从过电压保护中分离出能量吸收的思想，对传统直流固态断路器进行拓扑改进，通过引入续流二极管将故障电流旁路，从而实现了断路器的安全快速关断。在Matlab/Simulink中搭建模型进行仿真验证，将所搭建的直流固态断路器应用于三端环形直流微电网，成功切除故障线路并且避免了微电网因为故障而崩溃，仿真结果证明了该直流固态断路器在环网中的有效性
4、和可行性。关键词：直流微电网；固态断路器；缓冲电路；续流二极管；故障分析AbstractWith the development of global economy, the rapid growth of energy demand, especially for electric power demand is more prominent, environment problem is increasingly serious. Under the double pressure of energy demand and environmental protection, distrib
5、uted generation has been widespread concern. In order to maximize the value of distributed generation, the concept of microgrid emerges. DC microgrid has advantages of simple control, low conversion loss and better load capability. Based on low voltage loop-type dc microgrid, the dc line fault and d
6、c solid-state circuit breaker are analyzed in this dissertation, it will provide technical support to promote the engineering application of dc microgrid.Firstly, the topology of microgrid, each port components and the equivalent circuit model of dc line are described in this dissertation. Based on
7、the structure of four terminal low-voltage loop-type dc microgrid, the characteristics of the fault current on the dc bus are analyzed in detail when the most severe fault occur in dc line. The particularity between fault and protection in dc microgrid has been summarized. Demand for dc solid-state
8、circuit breaker has been proposed based on the results of the analysis.Secondly, the dissertation analyzes with the voltage rating of 200V, capacity of 4kW loop-type DC microgrid. Performance analysis and parameter design of solid-state circuit breaker (SSCB) RCD snubbers are presented in a low-volt
9、age dc microgrid at dc-bus short circuit occurrence. When SSCB trips to block a line-to-ground or line-to-line short-circuit fault on the DC bus, the rapidly decreasing fault current will cause a transient overvoltage in the stray inductance of main circuit. The situation is especially grave in a li
10、ne-to-line fault which has a fault current of higher-magnitude. RCD snubbers are therefore added to suppress this overvoltage. Performance analysis of three commonly used RCD snubbers, i.e., charge-discharge-type, discharge-suppressing-type and discharge-suppressing-type , in a line-to-line fault ar
11、e presented in this paper. Three indexes are selected to provide an inner look into the charging and discharging process of the snubber capacitor during line-to-line fault, which are respectively: 1) the peak value of transient overvoltage in SSCB and the time length when it reaches steady state; 2)
12、 the peak value of fault current and the speed of energy transfer; 3) the peak value of snubber capacitor current and voltage. Using the same set of parameters, discharge-suppressing-type proves to obtain the best performance. The parameter design method of snubber capacitor, inductor and diode is a
13、lso given. Simulations verify the validity of performance analysis and the feasibility of the snubber.Finally, based on the limitations of traditional dc solid-state circuit breaker RCD snubbers, topology improvements have been proposed by using a freewheeling diode to bypass the fault current to re
14、alize the fast shut off safely. This way, the over-voltage protection can be separated from the energy absorption task of the RCD snubber. Simulation results verify the effectiveness and feasibility of the improved dc solid-state circuit breaker to meet the needs of rapid removal of fault current in
15、 three terminal loop-type dc microgrid.Keywords: DC microgrid; solid-state circuit breaker; snubber circuit; freewheeling diode; fault analysisVII目 录摘要IAbstractIII1 绪论11.1 研究背景与意义11.2 直流微电网国内外研究现状21.3 直流微电网保护技术研究现状51.4 论文的主要工作与章节安排71.4.1 本文的主要工作71.4.2 本文的章节安排72 直流微电网结构与故障机理分析92.1 直流微电网拓扑结构92.2 分布式微电源和储能装置102.2.1 分布式微电源112.2.2 储能装置132.3 直流线路等效模型142.4 直流线路故障机理分析152.4.1 线路故障类型162.4.2 直流线路故障过程机理分析172.4.3 直流微电网线路故障与保护的特殊性212.5 直流微电网保护设备概述222.6 本章小结233 直流固态断路器拓扑及工作特性研究253.1 直流断路器常见拓扑253.2 RCD缓冲电路工作原理283.3 三种RCD缓冲电路性能分析303.3.1 充放电型RCD缓冲电路323.3.2 放电阻止型RCD缓冲电路353.3.3 放电阻止型RCD缓冲电路393.3.4 三种缓冲电路
