含MMC-HVDC的交直流混合系统保护方案及其改进研究

发布时间：2019-03-17 09:48

【摘要】：近年来,随着直流输电技术的进步,柔性直流输电因其可控性强、不存在换相失败问题、易于构建多端直流系统等优点得到快速发展。模块化多电平换流器(Modular Multilevel Converter,MMC)具有高度的模块化结构、可以扩展到任何电压等级、波形质量高和故障处理能力强等特点,在柔性直流输电实际工程中得到广泛应用。随着直流系统容量的增加,强耦合情况下的混合系统在电网调度、协调控制等方面存在许多新的问题。对于含MMC-HVDC的交直流混合系统,其继电保护的动作机理和配置都与传统交流系统存在较大区别。本文对这一问题开展研究,对现有继电保护配置进行总结,在分析接入MMC-HVDC的交直流混合系统中存在的不正确动作基础上,提出保护改进方案。本文首先按照保护对象的不同,将含MMC-HVDC的交直流混合系统划分为不同的保护区,对现有继电保护配置进行了总结。然后,从谐波影响、距离保护存在拒动、零序电压保护误动方面分析了接入MMC-HVDC的交直流混合系统中存在的不正确动作问题。在谐波影响方面,研究了MMC电平数、交流系统参数与输出谐波特性的关系,分析了由于谐波含量大和保护装置选择不合理而造成的误动。在此基础上,提出了防范措施,避免误动的发生。在距离保护方面,深入研究了MMC-HVDC系统运行方式对交流线路距离保护的影响,揭示了距离保护Ⅱ段发生拒动的原因。从整定方法上出发,提出了基于公共连接点处量测信息的自适应距离保护方法能够克服MMC-HVDC对距离保护Ⅱ段的影响。这样可以避免出现因保护覆盖下一线路过短时,本线路末端短路故障引起的距离保护Ⅱ段保护拒动的风险,减小了故障的清除时间,对电力系统的稳定运行具有重要的意义。在零序电压保护误动方面,建立了MMC平均值模型和零序等值网络,推导出MMC-HVDC系统的零序电压关系式,着重分析了零序电压保护误动的机理,并提出了保护改进方案。最后通过仿真验证所做分析和所提改进方案的有效性。
[Abstract]:In recent years, with the development of HVDC technology, flexible HVDC transmission has been rapidly developed due to its strong controllability, no commutation failure and easy to build multi-terminal HVDC system. Modular multilevel converter (Modular Multilevel Converter,MMC (Modular multilevel Converter), with its high modularization structure, can be extended to any voltage level, high waveform quality and strong fault handling capability. It has been widely used in the practical engineering of flexible DC transmission. With the increase of DC system capacity, there are many new problems in power network dispatching and coordination control of hybrid systems with strong coupling. For AC / DC hybrid system with MMC-HVDC, the action mechanism and configuration of relay protection are different from those of traditional AC system. This paper studies this problem and summarizes the existing relay protection configuration. On the basis of analyzing the incorrect action of AC / DC hybrid system connected to MMC-HVDC, the protection improvement scheme is put forward. In this paper, according to the different protection objects, the AC / DC hybrid system with MMC-HVDC is divided into different protected areas, and the existing relay protection configuration is summarized. Then, the problem of incorrect operation in AC / DC hybrid system connected to MMC-HVDC is analyzed from harmonic effect, distance protection and zero sequence voltage protection misoperation. In the aspect of harmonic effect, the relationship between MMC level, AC system parameters and output harmonic characteristics is studied, and the misoperation caused by large harmonic content and unreasonable selection of protection device is analyzed. On this basis, the preventive measures are put forward to avoid the occurrence of misoperation. In the aspect of distance protection, the influence of the operation mode of MMC-HVDC system on the distance protection of AC lines is deeply studied, and the reasons for the failure of distance protection in the second section of distance protection are revealed. Based on the tuning method, an adaptive distance protection method based on the measurement information at the common connection point is proposed, which can overcome the influence of MMC-HVDC on the distance protection stage 鈪，

本文编号：2442172