直流电网中VSC的双极短路故障分析与保护技术研究

发布时间：2018-11-21 17:59

【摘要】：由于用户对电能质量要求的提高和用电负荷的增长,传统交流电网正面临越来越多的挑战。基于全控型整流器件及脉宽调制的直流电网技术,以其控制灵活、即插即用、电能损耗低以及潮流转换方便等优点,正逐渐成为未来电网发展的趋势。然而由于实际工程经验的缺乏和直流断路器技术发展的限制,直流电网的保护研究成为制约直流电网系统发展的瓶颈。本文以直流电网系统为研究对象,重点研究了系统中VSC的数学模型及控制方法,不同拓扑下直流电网中VSC的故障暂态分析和故障的检测与隔离。1、建立了abc三相静止坐标系和dq两相旋转坐标系下VSC的数学模型,对VSC换流站的双环控制方法进行了研究,设计了基于电流前馈补偿解耦的电流内环控制策略,并分别对定直流电压、定有功功率等外环控制方法进行了讨论,实现了有功和无功功率的解耦控制。2、着重讨论了不同直流电网拓扑结构下VSC的双极短路故障特性。对于双端直流系统,将故障过程分为电容器放电阶段、二极管续流阶段以及不控整流稳态阶段,分别对各阶段电流电压等暂态量进行了求解。对于多端直流树状系统以及环网系统,对故障电路进行了等效简化,推导出了故障后电流的暂态表达式。3、对直流电网保护技术中故障检测和故障隔离方法进行了研究。在故障分析基础上结合线路出口限流器、直流断路器及直流方向开关的使用,提出了一种基于故障特征量di/dt的无需换流站间通信的故障检测方法。针对目前大容量直流断路器研发困难和交流断路器独立使用时可靠性较差的问题,结合故障后换流器电流的暂态特性,提出一种由交流断流器和小容量直流断路器的配合使用的故障隔离方法,最后通过仿真验证了故障检测和隔离方法的有效性。
[Abstract]:Traditional AC power grid is facing more and more challenges due to the improvement of power quality requirements and the increase of power load. Based on full control rectifier and pulse width modulation, DC network technology is gradually becoming the trend of power grid development in the future because of its advantages of flexible control, plug and play, low power loss and convenient power flow conversion. However, due to the lack of practical engineering experience and the technical development of DC circuit breakers, the research of DC network protection has become a bottleneck restricting the development of DC network system. In this paper, the mathematical model and control method of VSC in DC network are studied, and the fault transient analysis and fault detection and isolation of VSC in DC network under different topologies are studied. The mathematical models of VSC in abc three-phase stationary coordinate system and dq two-phase rotating coordinate system are established. The double-loop control method of VSC converter station is studied. The current inner loop control strategy based on decoupling of current feedforward compensation is designed. The methods of constant DC voltage and constant active power equal outer loop control are discussed, and the decoupling control of active and reactive power is realized. 2. The characteristics of bipolar short circuit fault of VSC under different DC network topology are discussed emphatically. For the two-terminal DC system, the fault process is divided into capacitor discharge stage, diode continuous current stage and uncontrolled rectifier steady-state stage. The transient parameters such as current and voltage in each phase are solved respectively. For multi-terminal DC tree system and ring network system, the fault circuit is equivalent simplified, and the transient expression of fault current is derived. 3. The fault detection and fault isolation methods in DC network protection technology are studied. On the basis of fault analysis, a fault detection method without communication between converter stations is proposed based on fault characteristic di/dt, combined with the use of line outlet current limiter, DC circuit breaker and DC directional switch. In view of the difficulties in developing large capacity DC circuit breakers and the poor reliability of AC circuit breakers when they are used independently, combined with the transient characteristics of converter current after fault, A fault isolation method is proposed, which is used in combination of AC current breaker and small capacity DC circuit breaker. Finally, the effectiveness of fault detection and isolation method is verified by simulation.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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