广州电网柔性直流输电系统对继电保护影响的研究

发布时间：2018-11-04 07:47

【摘要】：随着广州电网网架结构的完善,其供电能力及可靠性逐步提高,同时,在电源不断投产、负荷水平持续增长等影响下,电网的短路电流呈持续增长的趋势。利用柔性直流输电系统能够独立控制所传输的有功和无功的能力,提高电网供电可靠性、动态无功补偿能力和电网调度运行的灵活性。但协调控制系统的控制方式灵活多变,针对交流系统故障可以设计其控制系统,抑制负序分量,改变传统故障的故障特性,对交流线路上的传统保护可靠性产生了影响。因此,针对电网交流线路发生故障时,研究柔性直流输电系统的控制方式及其对交流保护的影响变得尤为迫切。首先,本文对MMC换流器的拓扑结构、工作原理及调制控制策略等方面进行了研究,基于基本理论搭建相应的系统稳态仿真模型;接着,针对交流线路发生故障时,依据信号延迟法提取电网电压和电流的dq轴正负序分量,提取正序分量进行锁相的改进,对负序分量进行数学建模并设计负序电流控制器,仿真结果表明,该负序电流控制器可以抑制掉负序电流分量,使得换流器输出的交流电流具有三相对称的特性;然后,基于距离保护的基本原理,推导了柔性直流输电系统的控制系统中负序电流控制器的投入运行对其测量阻抗不产生影响,得出了不改变其动作可靠性的结论,由于负序电流控制器投入运行影响了负序网络,进而影响了零序电流大小;最后,针对交流线路发生故障时,控制系统中的负序电流控制器投入运行后,抑制掉负序电流,三相电流突变量相等,从而电流突变量的故障选相元件失效。基于故障相的相电压降低的故障特性,选择了低电压故障选相元件。本文针对交流电网发生故障的工况,设计了控制系统的负序分量控制策略,理论推导分析了该控制策略对交流线路距离保护、零序电流保护、电流突变量选相元件等保护的影响,在仿真软件上搭建相应的模型验证理论结论。本文结论为柔性直流输电系统的接入交流系统的保护配置和整定提供一定的理论基础,为电网的安全稳定运行提供保障。
[Abstract]:With the improvement of the grid structure in Guangzhou, the power supply capacity and reliability are improved gradually. At the same time, under the influence of power supply and load level, the short-circuit current of power grid is increasing continuously. The flexible direct current transmission system can independently control the active and reactive power transmission, improve the reliability of power supply, dynamic reactive power compensation and the flexibility of power dispatching. But the control mode of the coordinated control system is flexible and changeable. The control system can be designed for the fault of AC system, which can suppress the negative sequence component and change the fault characteristic of the traditional fault, which has an impact on the reliability of the traditional protection on the AC line. Therefore, it is urgent to study the control mode of flexible DC transmission system and its influence on AC protection. Firstly, the topology, working principle and modulation control strategy of MMC converter are studied, and the corresponding steady state simulation model is built based on the basic theory. Then, according to the signal delay method, the positive and negative sequence components of the dq axis of the grid voltage and current are extracted, and the phase-locking improvement is carried out. The mathematical model of the negative sequence component is established and the negative sequence current controller is designed. The simulation results show that the negative sequence current controller can suppress the negative sequence current component and make the AC current output of the converter have the characteristic of three-phase symmetry. Then, based on the basic principle of distance protection, it is deduced that the operation of negative sequence current controller in the control system of flexible direct current transmission system has no effect on its measuring impedance, and the conclusion is that the reliability of its operation is not changed. Because the negative sequence current controller is put into operation, the negative sequence network and the zero sequence current are affected. Finally, the negative sequence current controller in the control system can suppress the negative sequence current when the fault occurs in the AC circuit, and the three-phase current mutation amount is equal, so the fault phase selection element of the current mutation quantity is invalid. Based on the fault characteristics of the phase voltage reduction of the fault phase, the low voltage fault phase selection element is selected. In this paper, the negative sequence component control strategy of the control system is designed for the fault condition of AC power network, and the control strategy for AC line distance protection and zero sequence current protection is deduced and analyzed theoretically. The effect of current sudden change phase selection element on the simulation software is built to verify the theoretical conclusion. The conclusion of this paper provides a certain theoretical basis for the protection configuration and setting of the access AC system of the flexible direct current transmission system, and provides the guarantee for the safe and stable operation of the power network.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1;TM77

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