基于模态切换的交直流混联电网故障的系统属性解析与直流保护策略优化

Protection has both "equipment / component attribute (referred to equipment attribute)" and "grid / system attribute (referred to as the system attribute)." The system attribute is further enhanced in AC-DC hybrid system. It expand the spatial and temporal scales of power system fault analysis. It may lead fault feature to transmission, coupling and even variation between AC and DC system. Actual operating experience has shown that this has become a bottleneck restricting the protection and the safe operation of the power grid..This research aims at the challenges of fault system attribute to HVDC protections in AC-DC hybrid system. According the response from the DC core essence: responding and switching of valve statuses and control modes, the HVDC fault analysis models are setup. Then the impact and factors and their associated side effects of system attributes are analyzed. The dynamic characteristics of the HVDC relaying quantities are firstly studied considering the effect of fault condition, system operation condition, and control system behavior. The study results clarify the boundary, constraint condition, and function of the protection criterions, which in turn gives a basis for the setting determination and optimization of HVDC protective relaying. By doing so, we effectively solve the problem of lacking efficient method for the setting determination and performance evaluation of HVDC protections, and incorporate the problem into the framework of conventional power system protection.

继电保护同时具有“设备/元件属性（简称设备属性）”和“电网/系统属性（简称系统属性）”。交直流混联系统故障的系统属性进一步增强、放大，一方面扩大了电力系统故障分析的空间尺度和时间尺度；另一方面可能引发故障特征在交直间传递、耦合甚至变异。实际运行经验表明，这已成为制约继电保护乃至整个电网安全运行的瓶颈。.本项目针对交直流混联系统故障系统属性对直流保护的挑战，从直流响应本质核心：阀状态和控制模式及其转化入手建立故障分析模型，对故障系统属性特性、关联因素及其作用边界展开分析，在此基础上提出直流保护协调优化策略。从故障的系统属性带来的影响和约束出发对继电保护动作行为评估无疑是一种新思路，突破了传统保护一时一地分析的局限性，对提升直流保护技术水平和驾驭交直流混联系统能力，防止复杂大系统灾变事故的发生具有重大意义。

本项目针对交直流混联系统故障系统属性对直流保护的挑战，从直流响应本质核心：阀状态和控制模式及其转化入手建立故障分析模型，对故障系统属性特性、关联因素及其作用边界展开分析，在此基础上提出直流保护协调优化策略。项目主要成果如下：.1. 从阀换相过程的物理本质入手，分析了换流器正常换相与换相失败的暂态过程；梳理了换流器区的故障类型及其电气特征，明确了影响模态切换的主要因素是故障类型、故障时刻、直流运行方式。通过对换流器故障动态分析，建立了综合考虑故障发生时刻、故障类型以及工作状态切换的换流器故障分析模型。.2. 直流控制系统的动态行为与换流母线电气量密切相关，交流系统故障还可通过直流控制间接引发换流器暂态。研究发现直流换相失败与交流故障点的空间位置和潮流密切相关，在复杂大电网下，故障点正常运行电压相位超前换流母线越多，或故障点与换流母线间互阻抗越小时，换相失败风险越低，反之，风险越高。故障点的节点阻抗情况相近时，稳态相位的影响起主导作用。.3. 研究了直流系统故障响应与直流控制保护的关联性。研究表明直流在交流故障期间存在发生后续换相失败的风险来源于两方面：一是直流两侧独立配置的VDCOL使得整流侧无法感知逆变侧故障后续恢复情况提前升高电流参考值，二是定关断角控制器比较环节中直流电流偏差量的引入可能会掩盖关断角变化的真实趋势。并根据故障响应与控制保护的关联性给出了有利于直流运行的相关建议。.4. 针对基于电气幅值特征信息的直流保护对区外交流故障响应的不足和瓶颈，充分利用电气量的幅值特征和时序特征相结合表征区外交流故障换流阀本身的运行状态，对直流保护进行优化。从换流阀的换相过程和导通过程出发，构建一种全新的换相异常保护方法以及阀状态检测方法。新构造的检测方法能够快速、准确的对异常阀状态进行判别，且兼具有效性和鲁棒性。