柔性直流换流平台关键设备轻型化是实现海上风电经济高效送出的关键问题。从现有柔性直流换流站的桥臂电抗器设计方案出发，提出了柔直变压器复用型桥臂电抗器和分布式桥臂电抗器两种轻型化桥臂电抗器方案，并且阐述了两种轻型化方案桥臂电抗参数的设计方法。基于PSCAD/EMTDDC仿真软件分别建立了采用两种轻型化桥臂电抗器方案的海上风电经伪双极柔性直流送出系统模型，对比分析了轻型化桥臂电抗器方案和传统桥臂电抗器方案的系统稳态特性和暂态特性。结果表明，采用两种轻型化桥臂电抗器方案，发生直流双极短路故障后，桥臂电流最大值不超过1.2p.u.，且子模块电容电压不会大幅下降。当换流器闭锁时，轻型化桥臂电抗器方案的变压器阀侧电压与传统桥臂电抗器方案相比更低。

基于MMC（模块化多电平换流器）的SCES（超级电容储能系统）是解决大规模可再生能源并网问题的关键技术之一，但超级电容的差异性将导致SOC（荷电状态）不一致，从而影响储能容量利用率。针对此问题，提出一种基于电容电压平衡的MMC-SCES荷电状态均衡控制方法，通过储能功率的改变和子模块电容电压平衡实现各级SOC均衡。在PSCAD/EMTDC中搭建双端输电系统验证所提控制策略的可行性和有效性。结果表明：所提出的SOC均衡策略大幅减少了控制器的数量，简化了控制系统；采用状态排序与增量投切的电容电压平衡控制策略可以在SOC均衡的同时有效减少IGBT开关次数，降低了开关损耗。

Aiming at the problem that a LCC-HVDC transmission system is apt to cause continuous commutation failures (CCF) under an AC fault on the inverter side, this paper analyzes the mechanism of CCF in stages. It is clear that when the firing angle deviation occurs, the mismatch between the DC current and the actual firing angle is an important cause of the CCF. If an asymmetric fault occurs at that time, the negative sequence component affects the actual firing angle through the pole control and the valve control system, which may increase the risk of CCF. Therefore, a CCF suppression method based on the actual firing angle response is proposed, in which the current command of the rectifier side is corrected by the actual firing angle. At the same time, the method reduces the influence of negative sequence current on the command of firing angle of pole control by the notch filter, and reduces the influence of negative sequence voltage on the actual value of firing angle of valve control by the sequence decoupled resonant and the commutation voltage phase compensation. This method is able to realize the dynamic and adaptive current command adjustment, improve the matching degree between the DC current and the actual firing angle in the recovery process, and promote the ability of DC system to resist the CCF. In the CIGRE model and an engineering model, the correctness of the theoretical analysis and the effectiveness of the optimization method are verified. © 2024 Power System Technology Press. All rights reserved.

The thyristor converter is a core equipment for AC/DC hybrid power grids of high-voltage direct current (HVDC) where overheating does harm to its reliability. In reality, overheating is closely related to the broken three-phase symmetry when the AC side is disturbed. Particularly, when commutation failures occur, the valve forced to reconduct will suffer from severe short-circuit current for a long period, risking the overheating damage. Therefore, the accurate measurement of valve current is fundamental to acquire valve temperature. This paper adopts a real-time virtual measurement scheme, which is based on temporal features of the converter terminal current, to calculate valve current fundamental for the calculation of valve loss under the transient state. Then, an equivalent circuit model is built based on the actual heat-flow path of the converter valve, considering the high thermal sensitivity of the heat source material layer. Next, a monitoring system for transient valve temperature is established. Finally, the proposed method is tested in CIGRE HVDC benchmark model. The simulation results indicate that the proposed method can reflect the actual valve state, and model the actual heat transfer process more accurately compared to the Foster network, which can support the basic configuration of the overheat protection. (c) 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Commutation failures (CFs) caused by AC faults of the receiving-end system are regarded as a classical faulty event in multi-infeed LCC-HVDC systems, and reasonable configuration of synchronous condensers can effectively reduce the CF risk. Simulation and actual power grid operation experience show that CF caused by faults has probability characteristics, ignoring the CF probability may make the synchronous condenser's configuration inaccurate. In this paper, a method for the optimal allocation of synchronous condensers considering the CF probability is proposed to reduce CF risk in multi-infeed LCC-HVDC systems. First, a CF risk index is proposed, which can represent the relationship between the probability and severity of CF. The CF risk index considers the impacts of the types, locations, and occurrence time of AC faults on CF and the impacts of CF on the receiving-end system. Second, a fast and accurate calculation method for the CF risk index is proposed based on the voltage drop and AC-DC voltage asymmetry factor methods, which improved the accuracy and efficiency of theoretical calculations. Third, the optimal configuration model of synchronous condenser is established to reduce the CF risk index and cost, which can simultaneously optimize the number, size, and placement of synchronous condensers. Finally, an optimal allocation of synchronous condensers is demonstrated through genetic algorithm in the modified IEEE 118-bus system to show the effectiveness of the proposed method.

随着新型电力系统的建设，电网的“双高”将显著影响电力系统的运行与稳定特性。本文提出了一种光伏并网稳控系统的标准化设计方案，包括组网通信架构、软硬件功能配置、出口方式设计和协调配合方法等，解决了目前光伏稳控出口仅能在“全站整切”或“全站整调”中人为二选一的局限性。该方案已成功应用于南方电网首个水光互补项目，RTDS仿真试验结果表明，所设计的稳控系统实现了功率快速精细化调节，功率调节速度快，通信延时短，通信组网可靠性高，能够适应实际电网的各种稳定性需求。

提出了一种适用于风电并网地区的电网等值方法，满足大规模风电并网场景下对地区电网进行详细仿真的模型需求。与聚焦于主网的传统动态等值不同，风电富集地区电网等值不仅要考察风电在地区电网中密集接入的特点，圈定各个风电场站影响范围，而且还要在边界节点上综合考虑外网的源、荷特性约束，从而在保持稳态、暂态特性一致的前提下对外网进行大规模化简，实现地区电网的等值建模。首先，突破在风电场站接入点仅以短路比等电气强度指标来等效电网的传统方案，提出以节点残压来界定待研究区域与待等值外部区域；其次，考虑地区电网的拓扑约束对地区电网进行进一步化简；再次，考虑在边界节点上以等值同步发电机与复合负荷的组合形式构建外部系统的等值模型；最后，利用所提方法对实际风电富集地区电网进行了验证。仿真结果表明了所提等值方法的有效性。

针对逆变侧交流故障下LCC-HVDC输电系统易引发连续换相失败问题，本文分阶段分析了连续换相失败的产生机理。明确了当产生触发角偏差后，直流电流调节效果与实际触发角不匹配是连续换相失败的重要诱因。同时不对称故障后，负序分量通过极控、阀控两级控制系统对实际触发角造成的影响，增加连续换相失败的风险。因此提出了一种基于实际触发角响应的连续换相失败抑制方法，通过实际触发角修正整流侧电流指令值。与此同时，该方法通过陷波器降低负序电流对极控层触发角指令值的影响，通过相序解耦控制器和换相电压相位补偿降低负序电压对阀控层触发角实际值的影响。该方法能实现动态、自适应的电流指令值调整，提升恢复过程中直流电流与实际触发角的匹配度，提升直流系统抵御连续换相失败能力。在CIGRE标准测试模型和实际工程模型中，验证了理论分析的正确性和优化方法的有效性。

Commutation failure (CF) increases the current flowing through the converter and endangers the converter. To protect the converter, CF protection is used in high voltage direct current systems. The core of CF protection is accurate CF detection. Owing to the nonlinear characteristics of converter and the rapid control, the conventional differential current method used to detect CF faces challenges. This article proposes a method to detect CF directly by tracking commutation process. The study indicates that the characteristics of commutation process differ significantly between normal operation and CF. By extracting these characteristics, commutation process can be tracked, and CF can be detected. For improving reliability, the proposed method depends on the relative relationship between AC current and DC current, reducing the influence of current fluctuation. Temporal and amplitude characteristics are both extracted to judge commutation process state and detect CF. The performance of the proposed scheme is validated using an actual engineering model and recorded engineering data. The results indicate that the proposed method can effectively detect CF under different scenarios.