The additional current-limiting control of modular multilevel converters (MMC) can effectively reduce the technical demand for DC circuit breaker (DCCB). At the same time, in cooperation with the protection, it can effectively reduce the requirements for line protection speed and improve the reliability of the protection. Therefore, a pilot protection scheme considering the influence of additional current-limiting control is established by using the ideal of integration of control and protection. Firstly, a two-stage current-limiting control strategy is proposed based on the current changing rate and amplitude, which effectively limits the fault current. Secondly, a pilot protection principle of current mutational volume is proposed, which is based on the additional current-limiting control strategy and fault current mutational direction characteristic information. Finally, the performance of the additional current-limiting control strategy and proposed protection principle are verified in PSCAD. The simulation results show that the proposed current-limiting control strategy can effectively reduce the DC fault current; The proposed protection method can reliably identify the fault. At the same time, it has a certain immunity to noise and higher fault resistance interference.

To improve the ability of rapid fault clearing of hybrid multi-terminal High-voltage direct current transmission (HVDC) lines and ensure the safe operation of electric power transmission, a principle of hybrid HVDC system pilot protection based on the structure similarity for the of transient energy waveform is proposed. In this paper, the fault additional network diagrams of the S-domain under different fault conditions are analyzed, and it is found that there are differences in the transient power of the protection measurement points at both ends of the line during internal or external faults. On this basis, the time-domain transient power obtained by time-domain voltage and current convolution is used to characterize the S-domain power characteristics. Integrate the transient power in the time domain and obtain the transient energy waveform through a sliding window. Structural similarity is used to compare the similarity of transient energy waveforms at both ends of the transmission line, to identify internal and external faults and select fault poles. Simulation verification based on PSCAD/EMTDC shows that the proposed protection principle can reliably identify the fault area and fault pole in the case of 300 Ω fault resistance and 30dB noise interference. It is highly resistant to fault resistance and noise interference. Besides, it is not affected by transient processes and can achieve protection quickly.

Wind power Full-DC transmission system can effectively solve the problems of harmonic and reactive power compensation that exist in wind power AC collection and transmission, and has broad development prospects. It contains a large number of power electronic converters. These power electronic converters have a limited ability to withstand overcurrent. Therefore, researching fast and accurate fault identification line protection is an urgent need for the development of DC power grids. This article analyzes the attenuation characteristics of the initial traveling wave frequency component at the installation site of internal and external fault. Since the difference in attenuation of the initial traveling wave frequency component of internal and external faults. The paper proposes a single terminal protection based on the high and low-frequency ratio of initial voltage backward traveling wave. Finally, a four-terminal wind power full-DC transmission system model is established and verified using PSCAD/EMTDC. Theoretical analysis and simulation results show that the proposed protection scheme can correctly internal and external faults, accurately select fault poles, setting is simple and easy to operate, with strong resistance to fault resistance.

This paper reports a novel method of calculating short-circuit current for DC grid with complex topology. The transient process of a DC fault is divided into three stages, and this paper focuses on the DC line fault current during SM discharging stage, which will cause the most serious overcurrent results. Firstly, the equivalent model of SM discharging is built, and the corresponding state equation is deduced based on SM discharging meshes. Then, in order to identify the discharging meshes and establish state equation for a complex DC grid topology, a new method with four steps is proposed. The given method first numbers all the grid nodes, and then determines the discharging meshes of converter node and surplus branches. The proposed method can be extend to DC grid with complex topology. Two test systems with different topologies are used for simulation, and the comparison results between simulation and calculation results demonstrate the validity of the proposed method.

After an asymmetric fault occurs in a two-terminal weak feed AC system, negative sequence components affect the safe and stable operation of the power system may occur. Therefore, it is necessary to suppress the negative sequence component to improve the stability and reliability of the power system. In this paper, the overcurrent and overvoltage problems caused by negative sequence current · suppression control strategy and negative sequence voltage suppression control strategy on modular multilevel converter (MMC) side are compared. Then, a new control strategy is proposed, which uses the step-down V/ $f$ control strategy and the negative sequence current suppression control strategy on the MMC side to quickly limit the fault current amplitude and effectively avoid the non-fault phase overvoltage. After theoretical analysis and PSCAD simulation, analyze the electrical quantity changes under different types of control strategies. The simulation results show that the proposed fault control strategy effectively limits the negative sequence current amplitude and non-fault phase overvoltage. Under different control strategies, the electrical characteristics of the system vary significantly. The above characteristics can provide a theoretical basis for the analysis of protection adaptability and the study of new protection principles.

With the development of society, the demand for electricity continues to increase, and the scale of the power grid continues to expand. The transmission corridor is facing the problem of resource constraints, which leads to the inevitable occurrence of cross crossing of HVDC transmission lines. These cross lines may have mutual effects. Moreover, due to the complex and volatile environment in which HVDC transmission lines are located, the probability of a fault occurring on cross crossing lines is increasing, reducing the reliability of transmission lines. Therefore, for the planning, design and operation of power system, reliability assessment of transmission line crossing point is very important. In this paper, considering the complex environmental factors of HVDC transmission lines, a three-dimensional model of transmission lines under wind bias conditions, a calculation model of the impact of ice weight on sag of transmission lines under icing conditions, and a probability model of trip failure at crossing points of transmission lines under mountain fire conditions have been established. Based on an HVDC transmission project in China Southern Power Grid, the reliability of transmission line crossing points is evaluated, the factors that affect the occurrence of faults at the crossing points are analyzed, and sensitivity analysis is conducted. A reliability improvement strategy for transmission line crossing points is proposed, providing decision-making reference for practical projects.

When aground fault occurs on double-circuit wind power outgoing lines, the conventional tripping strategy may inject negative sequence components into the system, as well as the traditional automatic reclosing scheme does not determine the fault feature before the reclosing, if it is reclosed to a permanent fault, stability of the power system will be affected. To solve the above problems, an intelligent tripping-and-reclosing strategy for grounding faults on double-circuit wind power outgoing lines is proposed, single-ended phase segregated switches are used in the strategy. Firstly, by establishing and analyzing the phase-to-phase coupling model of double-circuit wind power outgoing lines, a new tripping strategy that can avoid the injection of negative sequence components into the power system is proposed. Secondly, the capacitive coupling voltage characteristics are analyzed under transient and permanent faults, and the fault feature identification criteria based on the capacitive coupling voltage of double-circuit wind power outgoing lines is proposed. Finally, the new tripping and closing strategy are combined to form an intelligent tripping-and-reclosing strategy for grounding faults on double-circuit wind power outgoing lines. The PSCAD/EMTDC simulation verifies that the proposed strategy can avoid the injection of negative sequence components into the system and ensure the reclosing success rate and stability of wind power transmission lines under different ground fault types, fault locations and transition resistances.

The battery energy storage system(BESS) can effectively suppress the influence of randomness and volatility of distributed generation on the power grid. Therefore, it is widely used in microgrid. Aiming at the overcurrent problem of BESS during the recovery stage of voltage drop fault, A low voltage ride through strategy using dynamic limiting and reactive power coefficient compensation is proposed to improve in this paper. Firstly, the typical topology and control strategy of BESS are given. Then, the causes of the over-current problem are analyzed during the fault recovery stage. Finally, the mathematical relationship between the terminal voltage and the limiting value of the outer loop PI controller is established, and an overcurrent suppression strategy is proposed. Furthermore, the effectiveness of the strategy is verified base on PSCAD/EMTDC. The results show that the proposed LVRT strategy can effectively solve the over-current problem of BESS during the recovery process.

On the demand side, a large number of adjustable load clusters are connected to the distribution network as diversified stakeholders. In order to reduce its electricity cost and improve the local consumption rate of new energy, it is necessary to study the fine control strategy of adjustable load cluster to guide its optimal operation when connected to the distribution network. This paper proposes a demand-side adjustable load cluster control method. Firstly, a cooperative game model of multi-adjustable load cluster is established based on Nash negotiation theory. Then, the revenue is distributed in an asymmetric bargaining manner, and the objective function is decomposed into two subproblems: alliance cost minimization and intra-cluster revenue distribution. Finally, the alternating direction method of multipliers (ADMM) is used to solve the problem iteratively. The example verification shows that the proposed method has good convergence performance and computational efficiency, gives full play to the regulation potential of the adjustable load cluster, and effectively reduces the operating cost.

In the context of global energy transformation, it is particularly important to tap the potential of flexible load on the distribution network side to participate in grid operation. As an important flexible adjustable load in the distribution network, air conditioning loads have typical characteristics of thermal energy storage, rapid response, and flexible scheduling, which is an ideal load resource. Effective and reliable load aggregation technologies for air conditioning load participation are the basis for operation in a power grid. To better understand the current research status of air conditioning load aggregation technologies and make full use of the existing research results to carry out further research, this paper comprehensively reviews the various aggregation technologies being used in distribution networks, including the modeling strategy for air conditioning load aggregation, control strategy, control method, and application analysis. Moreover, future research directions are summarized as a guide to improving the technology of air conditioning load aggregation.

The-wind-solar-thermal integration (WSTI) power base is an important technical mean to achieve carbon emission peak in China. A new optimal allocation model for the existing thermal power is given in this paper with the optimization target of maximum of new energy generation. In order not to increase the peak shaving pressure of power system, the additional regulation capacity of thermal power is used to bundle new energy resources, and the constraint of source-load similarity is intrduced for the first time. The source-load similarity is evaluated from two dimensions, namely fluctuation index and similarity index. The intelligent optimization algorithm is taken to solve the model. The proposed method can increase the electrcity production of new energy and efficiency of electric transmission line. Finally, an optimization model is built, and the simulation results prove the effectiveness of the proposed method.

Most of the existing power quality monitoring devices are mainly based on the internal clock to achieve time synchronization. However, due to the clock crystal oscillator error or damage and other problems, the monitoring device often has clock anomaly problems, which seriously affects the later data comparative analysis. In order to solve the problem of automatic detection of clock anomaly in power quality monitoring device, a clock anomaly detection method based on voltage sag homologous identification is proposed according to the characteristics of fast propagation speed and negligible time deviation of voltage sag in the system. Firstly, the voltage sag waveform data recorded by different monitoring devices are identified by homology, and then the time deviation of the same sag event recorded in different monitoring devices is compared to judge whether the clock of the monitoring device is abnormal according to the time deviation. The simulation data and measured data are used to verify the method. The results show that the method can accurately detect the clock anomaly of power quality monitoring device, and is of good accuracy and feasibility.

Under the background that Beidou satellite communication system in China has been networked and commercialized, A remote centralized reading system of electric power metering based on Beidou space-time quantity is proposed in this article, with the establishment of the software and hardware platform of the system. The remote centralized reading system of power metering based on Beidou space-time quantity researched and developed by this research and development, combining Beidou satellite system with intelligent distribution network automatic operation management, and putting forward the research and development technical route and specific implementation scheme which focuses on the key function points of Beidou positioning. The test results show that the data transmission of the system is fast, stable and reliable, and remote real-time monitoring and data acquisition can be achieved.

Electric spring (ES) is an emerging power quality adjustment method that can effectively solve the power quality problem, especially voltage fluctuations caused by renewable energy sources. However, the existing topologies of ES have the shortcoming of limited compensation range due to their structure, in which ES is in series with non-critical load (NCL). In this paper, a novel ES is proposed based on a passively damped LCL filter. Unlike the existing ES topologies, LCL-ES employs NCL to implement passive damping of LCL filter, which not only overcomes the passive damping but also extends the compensation range. Besides, the key points on topology design and control strategy are discussed. Finally, the effectiveness of the proposed LCL-ES has been verified via simulation.

直流线路采用架空线和电缆混合的拓扑结构时,会造成频谱混叠,影响固有频率主频的提取,故障距离和固有频率的关系也变得复杂.针对这一问题,提出一种基于VMD-后向预测prony来确定固有频率的直流混合线路故障测距方法.首先,通过VMD算法分解得到多个IMF分量;其次,选取暂态信息丰富的IMF分量,采用后向预测prony算法确定固有频率主成分对应的频率值,以确定故障区段;最后,根据对应区段线路的故障距离和固有频率的关系式计算故障距离,实现测距.仿真结果表明,该方法频率提取精度高,在保留固有频率法耐过渡电阻能力强的特点的同时,提高了故障测距精度.

For the power converter with multiple switches, different control methods can be obtained by combining the ON/OFF states of the switches. In this paper, a high voltage gain quasi-switched boost inverter (qSBI) is taken as an example to illustrate how to obtain all possible control strategies by applying the multi-modal combination control method. Then, one novel three-modal control method among all feasible control strategies is selected to compared with the existing control methods in detail. The simulation results verifies the advantages of the proposed three-modal control method, and proves the feasibility of the multi-modal combination control method.

针对采用模块化多电平换流器(MMC)的多端直流系统(MTDC)故障电流大、上升速度快,现有混合式直流断路器(DCCB)无法快速有效隔离故障区域的问题,提出一种新型故障处理策略.通过对比电感型超导限流器(I-SFCL)和电阻型超导限流器(R-SFCL)对短路电流的影响,选取更具限流优势的R-SFCL,结合实验建立其失超和恢复超导态的等效模型.在分析R-SFCL和DCCB配合原理的基础上,提出R-SFCL和DCCB配合的故障处理流程.基于舟山工程在PSCAD/EMTDC仿真平台上对所提新型配合策略加以验证,仿真结果表明该配合策略能够快速地隔离故障,实现非故障站的故障穿越,提高了MTDC系统的稳定运行能力.

Aiming at the problem of commutation failure often occurring in high voltage direct current (HVDC), the shortcoming of the existing voltage prediction criterion is analyzed based on the mechanism of commutation failure. By building the HVDC model and studying the transient process of HVDC after three-phase AC fault, a time-series segmentation method is proposed to calculate the post-fault transient DC current based on the post-fault AC voltage. Based on the method, an improved voltage prediction criterion of commutation failure simultaneously considering the DC current dynamics and the pre-fault operating state of HVDC is proposed, which can improve the accuracy of commutation failure prediction significantly. The feasibility and validity of the proposed current calculation method and improved voltage prediction criterion are verified by the comparison with the simulation results.

针对目前配网短路故障计算仅考虑配网部分的变化而未能反映主配网耦合关系及变压器影响的问题,提出一种基于端口补偿法的主配网暂降分析方法.根据配网拓扑和运行数据建立配网常态模型.并根据配网故障信息建立配网故障模型,结合变压器三序模型计算配网在变压器高压侧母线处的等值.建立主网模型时将配网常态等值计入主网节点导纳阵中,应用补偿法计算故障下的配网等值模型变化量对主网状态的影响.该影响值与故障前的网络状态量叠加后确定主网暂降状态,进而确定配网暂降状态,最终实现主配网暂降分析.通过对某城市电网系统进行仿真计算,验证了所提算法的可行性和有效性.

为了解决配电网面临的供电电压不合格和潮流分布欠优等问题,提出基于相变储能系统(PCMTESS)需求响应的配电网经济调度策略.介绍PCMTESS的构造和工作机理,分析热力侧的能耗规律,建立计及热耗散的热力侧和计及无功调节能力的电力侧封装模型.在此基础上,考虑潮流分布约束和分布式新能源出力特性,以配电网的购电成本最小化为目标,在综合考虑光伏、风机、负荷不确定性的条件下,建立统一的配电网调度模型.提出主、子问题交互迭代的求解策略,实现优化模型的高效求解.基于IEEE 41节点配电网的仿真结果表明,所提PCMTESS在维持室温舒适的前提下,能够优化配电网的潮流分布和改善电网的电能质量;所提调度模型为配电网的安全经济调度和综合能源消纳问题的解决提供了一个崭新的视角.