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      • GONG Zhen, SHEN Hanming, XIE Xiaorong, ZHANG Zhebo, YANG Lei, BU Yichen

        Available online:July 18, 2024  DOI: 10.7500/AEPS20240425008

        Abstract:In the grid-connected photovoltaic system, the maximum power point tracking (MPPT) control will introduce a large number of interharmonics of DC-link voltages, which may cause forced oscillations. Traditional research focuses on the relationship between the frequency of disturbance sources and the frequency of the inherent weak damping mode of the system, with less attention paid to the effect of converter control characteristics on exacerbating the forced oscillation. This paper takes the virtual synchronous generator (VSG) control as an example to construct a power input-output frequency-domain closed-loop transfer function model of the single-stage grid-connected photovoltaic system. It is pointed out that the interharmonics introduced by MPPT control will cause forced low-frequency oscillation in the photovoltaic system based on VSG control. Then the proposed model is compared with the the forced oscillation analysis method based on the traditional second-order time-domain differential equation. The equivalence property between the proposed closed-loop transfer function and the traditional second-order differential equation is proved. Thus, the influence of disturbance sources and converter control characteristics on the forced oscillation can be analyzed from the perspective of the frequency-domain input-output relationship. Finally, the influence mechanisms of the VSG overshoot effect and dynamic coupling effect of active and reactive powers on the forced oscillation are analyzed. The characteristics of the influence of VSG control overshoot and power coupling on the exacerbation of forced oscillation are verified by simulation cases.

      • CHENG Hao, LYU Yazhou, LI Wei, LIU Fusuo, LAI Yening, ZHANG Yudong

        Available online:July 17, 2024  DOI: 10.7500/AEPS20230914005

        Abstract:With the increasing penetration rate of the wind power, the massive wind farms entering into the low voltage ride-through (LVRT) at the same time will bring significant impacts to the power system, resulting in temporary drop in active power output, rapid drop in power grid frequency and even the risk of triggering under-frequency load shedding. It is necessary to quickly estimate the frequency curve of the power grid under the temporary power disturbances to develop corresponding control measures. However, due to the difference in ower recovery characteristics, LVRT curves present different shapes. If this impact is ignored, there will be significant estimation errors in the frequency response curve, and traditional time-domain simulation based on detailed model has low efficiency. Hence, a disturbance power analysis method considering LVRT recovery difference of wind farms is proposed. The disturbances caused by single-unit wind turbine at each stage of LVRT are discribed by segment functions, and the total temporary disturbance power of the system is accurately estimated based on energy conservation principle. Considering the frequency modulation characteristics of wind farm and the virtual inertia effect, an optimized model for system frequency response suitable for power girds of high-proportion renewable energy is proposed. The differental evolution algorithm is used to identify the parameters of the system transfer function based on actual data, and then the frequency response trajectory is fitted. The applicability and reliability of the proposed method in different scenarios are verified by the simulation of IEEE 39-node system and actual power grid simplified system

      • BAO Hai, SONG Weiyi

        Available online:July 17, 2024  DOI: 10.7500/AEPS20230923002

        Abstract:Scientific and accurate calculation of variable transmission costs is of great significance for the fair competition of electricity market. Through flow tracing, it is found that the transmitting power process from the power sources to electricity admittance components also generates active power losses, which in turn affects the final variable transmission cost. Therefore, when calculating the variable transmission cost, it is necessary to consider the physical and economic characteristics of the electricity admittance components. At first, a model is established to satisfy the power balance characteristics of active and reactive loads such as electricity admittance. Then, using the principle of cost conservation, a cost calculation model that conforms to economic characteristics is obtained. The variable transmission cost calculated using the proposed model can provide rich and accurate economic information. Finally, the rationality and accuracy of the proposed calculation model and results are verified through case analysis.

      • DONG Shufeng, ZHENG Xinyi, WU Zhenchong, GE Mingyang, LIAN Runzhe, XU Chengsi

        Available online:July 16, 2024  DOI: 10.7500/AEPS20240104005

        Abstract:The conventional energy management system exhibits intricate hardware components, high equipment access cost, limited scalability and generality, making it challenging to meet the requirements of multi-function autonomous management and control in small and medium-sized emerging scenarios. Therefore, an embedded energy management system is proposed. First, leveraging the hybrid control theory, the control configuration technology is introduced to achieve a comprehensive strategy development. Second, an edge optimization solver based on automatic differentiation is developed while constructing a lightweight Web application by integrating embedded database and asynchronous non-blocking communication technology. Finally, a semi-physical simulation test combined with Simulink is conducted to validate the effectiveness of the control approach. The embedded energy management system proposed in this paper has been successfully deployed at Century Substation of Hangzhou Asian Games Village as well as several industrial parks resulting in significantly reduced delivery cycle and deployment costs by over 50%, along with excellent performance.

      • LYU Yan, LI Li, SUN Lüe, LUO Yadi, CHEN Shu

        Available online:July 16, 2024  DOI: 10.7500/AEPS20240102003

        Abstract:In the background of the new power system, constructing typical source-load temporal scenarios can provide scenario support for the day-ahead or intra-day electricity production organizations. To further improve the quality of temporal scenarios generated by statistical methods, and reduce the number of typical source-load temporal scenarios, a method for generating typical source-load temporal scenarios based on the modification of sampling probability interval is proposed. Firstly, considering the historical fluctuation characteristics of renewable energy, the probability interval of the prediction error temporal sampling is modified, and the temporal scenarios are sampled and generated using Latin hypercube sampling at the first sampling point and using random sampling in modified probability interval at subsequent sampling points. Secondly, typical temporal scenarios are obtained based on clustering method. Then, the typical source-load temporal scenario combinations are reduced from the perspective of system security based on the source-load “AND” operation. Finally, based on actual data from a province in Northwest China, the source-load temporal scenarios for an IEEE 39-bus system are constructed to verify the effectiveness and feasibility of the proposed method.

      • FU Lerong, FENG Moke, XU Jianzhong

        Available online:July 15, 2024  DOI: 10.7500/AEPS20231202001

        Abstract:Modular multilevel converter with supercapacitor energy storage system (MMC-SESS) combines the advantages of MMC and supercapacitor energy storage system, and can be used in the large-scale transmission field of renewable energy. However, due to the submodule (SM) structure of MMC-SESS are more complex and the operation modes are more various, an electromagnetic transient equivalent model for MMC-SESS is proposed to increase the simulation efficiency under multiple types of transient and steady-state operation conditions, including steady-state, blocked start-up, DC fault blocking, etc. Firstly, the topology and operation modes of SMs in MMC-SESS are analyzed, and the adjoint circuits of a single submodule are obtained by using the two-value resistance and the trapezoidal integral discretization method. Afterwards, the Thevenin equivalent process adapted to the solution logic of EMTDC simulation platform is proposed to realize the equivalent simplification of SMs and bridge arms, and the overall equivalent circuit is obtained. In addition, the operation modes under blocked operation conditions are analyzed, and the blocked equivalent circuit is constructed and merged into the obtained overall equivalent model. Finally, the electromagnetic transient equivalent model of MMC-SESS is obtained under multiple operation conditions. It is verified by simulation in PSCAD/EMTDC that the proposed model has good simulation accuracy and efficiency.

      • ZHAO Jinquan, TANG Yi, DANG Jie, CUI Ting, CHEN Daojun

        Available online:July 15, 2024  DOI: 10.7500/AEPS20231210002

        Abstract:The voltage stability problem of power grids with high proportion of renewable energy is prominent, continuous power flow is an important tool for voltage stability analysis. The current continuous power flow of power grids with voltage source converter (VSC) power supply does not fully consider the various control modes and operational constraints of VSC, resulting in insufficient accuracy of voltage stability margin calculation. In this paper, a continuous power flow model and calculation method considering the output current constraint and internal potential constraint of renewable energy grid-connected VSC, constant voltage control and reactive power-voltage droop control of grid-forming renewable energy and constant reactive power control of grid-following renewable energy are proposed, and the control mode switching logic and bifurcation point type identification method caused by constraints are given. The results of a case with modified IEEE 39-bus system show that the proposed model and algorithm improve the applicability of the traditional continuous power flow method to the static voltage stability analysis of power grids with high-proportion of renewable energy.

      • ZHANG Ziru, FU Fenghao, ZHAO Xibei, JIA Xiufang

        Available online:July 15, 2024  DOI: 10.7500/AEPS20231116001

        Abstract:In the ultra-high voltage and long-distance DC transmission system using the half-bridge modular multilevel converter (MMC) with high/low voltage valve connection, the ultra-high voltage DC circuit breakers required for fault clearance are immature and costly. Aiming at the above problems, this paper proposes an embedded MMC topology with high/low voltage valve connection. According to the basic principle of full-bridge sub-module operation, an external embedded bridge arm and an internal embedded energy transfer branch are designed to reverse the voltage polarity of the MMC with the high voltage valve. The converter station of the half-bridge MMC can realize the non-blocking DC fault ride-through with a lower cost than that of the hybrid MMC. Based on the switching sequence of each branch and the switching time of different devices during fault clearing, the fault ride-through control strategy is designed. By analyzing the current and voltage stress of the device in each stage, the basis for device selection and number configuration is given. Finally, the effectiveness of the proposed control strategy is verified by PSCAD/EMTDC simulations. The device cost and operation loss of the proposed strategy are compared with the existing MMC schemes, which shows the proposed strategy is more economical.

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      Volume 48,2024 Issue 13

        >Review·Perspective
      • XU Shiyun, WANG Yiming, SUN Huadong, BI Jingtian, LAN Tiankai

        2024,48(13):1-8, DOI: 10.7500/AEPS20230808004

        Abstract:From 2016 to 2023, eleven significant outage accidents related to the renewable energy occurred in the United States, Australia, and the United Kingdom, which posed severe threats to the secure and stable operation of power grids. The basic situation of these accidents are introduced, and their instability process characteristics, and mechanism are summarized and analyzed. It identifies the insufficient system strength, irrational renewable energy control strategies, and a lack of unanticipated fault prevention measures as the primary reasons for these accidents. Finally, combined with the reality of the power grids in China, some recommendations are proposed to ensure the secure and stable operation of the new power systems.

      • >专栏:碳达峰·碳中和与电力能源转型
      • LI Jianlin, ZHAO Wending, LIANG Zhonghao, MIAO Huiyu, YUAN Xiaodong

        2024,48(13):9-18, DOI: 10.7500/AEPS20231209001

        Abstract:Photovoltaic (PV) electrolytic water hydrogen production technology is an important way of realizing PV accommodation and green power hydrogen production. In fluctuating power input state, there are many problems in the operation stability of the electrolyzer hydrogen production system and the economy of hydrogen production. Aiming at these problems, a PV hydrogen production strategy based on hybrid-electrolyzer hydrogen production system is constructed, using the combination of alkaline electrolyer (AEL) water hydrogen production systems and proton exchange membrane electrolyzer (PEMEL) systems, and the power optimal control technology and capacity configuration method of the hybrid-electrolyzer hydrogen production system are proposed. Based on the combined operation and reasonable configuration of different types of electrolyzers, the performance of hydrogen production is improved. Results show that the quantity of hydrogen production of the hybrid electrolyzer hydrogen production system is improved by 5% compared with the single AEL hydrogen production system. The fluctuation rate and the hydrogen production cost are dramatically reduced compared with the PEMEL hydrogen electrolytic water production system. With the adoption of the power optimization control technology, the quantity of the hydrogen production is increased in the operation state with the same power. When the single electrolyzer is in the fluctuating working condition, the array rotation mode is adopted to ensure the safe operation of the electrolyzer system.

      • YIN Deqiang, YAO Liangzhong, CHENG Fan, XU Jian, WU Ming, ZHAI Dongyang

        2024,48(13):19-29, DOI: 10.7500/AEPS20240108007

        Abstract:Hydrogen production from renewable energy, such as wind power, is an effective technical means to improve the accommodation capability for renewable energy. A power coordinated control method for DC microgrid with hydrogen-storage-wind power considering optimized operation requirements of hydrogen production efficiency is proposed, which can adapt to the wind power and load power fluctuations and ensure the efficient operation of the hydrogen production electrolyzer. According to the optimized operation area of the hydrogen production electrolyzer and the range of DC bus voltage fluctuations, the DC microgrid is divided into normal operation modes (i.e., optimized operation of hydrogen production electrolyzer) and extreme operation modes (i.e., non-optimized operation of hydrogen production electrolyzer). In the normal operation modes, the operation point of the electrolyzer is maintained within the optimized operation area through the self-adaptive droop control of the electrolyzer and the variable coefficient droop control with a virtual capacitor of the battery energy storage to ensure the efficient and safe operation of the electrolyzer. In the extreme operation modes, the voltage safety of the DC microgrid is assured through flexible switching control strategies of hydrogen and storage. The proposed coordinated control method can not only rapidly suppress the DC bus voltage fluctuations caused by the wind power and load power fluctuations, but also maintain the hydrogen production efficiency at a high level. Finally, the effectiveness and superiority of the proposed method are verified through simulation cases of PSCAD/EMTDC.

      • YUAN Tiejiang, ZHANG Yijin, GE Yangyang, TIAN Xueqin, YANG Zijuan

        2024,48(13):30-39, DOI: 10.7500/AEPS20230821002

        Abstract:The application of hydrogen energy in large scale and multiple fields has an impact on the scale, structure and distribution of electric load, which brings new challenges to the power source planning. To this end, a low-carbon planning model of power source considering cross-domain hydrogen loads is proposed. Firstly, taking into account the hydrogen loads in the fields of industry, transportation and heating supply, an electricity-hydrogen system structure is built containing conventional thermal power units, carbon capture units, renewable energy units and hydrogen energy systems, and the hydrogen demand in multiple fields is forecasted based on the system dynamics theory. Secondly, by introducing a tiered carbon trading mechanism, taking into account the demand for electricity and hydrogen loads and on the premise of satisfying the system conventional constraints and hydrogen energy equipment constraints, a low-carbon planning model of power source is constructed with the optimization objective of minimizing the sum of investment, operation, carbon trading and curtailment costs. Finally, the actual data of a certain region in northwest China is taken as an case for numerical analysis. The results indicate that the low-carbon power planning model after introducing hydrogen loads and carbon capture power plants can optimize the power source structure, improve the energy utilization efficiency, and reduce the system carbon emission.

      • CHEN Wei, WANG Yongheng, SHEN Xinwei, DU Yunfei

        2024,48(13):40-49, DOI: 10.7500/AEPS20230720001

        Abstract:With further promotion of the goals of carbon emission peak and carbon neutrality, the development of new energy vehicles has become an important approach to resolving carbon emission problems in the transportation-energy field. This paper proposes a synergistic planning method for photovoltaic-storage-charging stations and hydrogen refueling stations of vehicles considering carbon emission flows. Firstly, the spatiotemporal characteristics of new energy vehicles are sampled by using the Monte Carlo method. Considering the factors such as charging station locations, scales, and energy supply, the planning model is established with the goal of system economic optimization. Secondly, the carbon emission flow theory is introduced, and the carbon emission cost is incorporated into the objective function by combining the power flow calculation and power grid analysis methods. Finally, a case study is conducted on the active distribution network of a district in a city in South China. The planning results in the scenarios with different photovoltaic outputs and penetration rates of new energy vehicles are analyzed, and the effectiveness of the proposed method is verified.

      • >Basic Research
      • LI Yong, CHANG Fanrui, PENG Yanjian, GAO Yousong, ZHOU Nianguang, YU Haifeng

        2024,48(13):50-59, DOI: 10.7500/AEPS20230814004

        Abstract:Inertia plays a key role in the resistance of power system to disturbances. With the increase of renewable energy penetration, the characteristics of low inertia and uneven spatial and temporal distribution of inertia in the power system are becoming more and more prominent, and it is of great significance to accurately evaluate the node inertia distribution in the power grid. To this end, this paper proposes an evaluation method for node inertia distribution based on small disturbance frequency measurement data. First, the mathematical coupling mechanism between frequency and inertia is analyzed, and the inertia distribution characteristics of the new power system are revealed. Then, based on the frequency measurement data and system power supply parameters under a single small disturbance, a node equivalent inertia definition method considering the horizontal deviation of each node frequency compared to the change of the center frequency of the system, and a calculation method for the rate of change of the frequency of each node based on adaptive-order polynomial fitting are proposed, respectively. The node equivalent inertia can be calculated by combining the two methods under a single small disturbance. Further, in view of the fact that the node equivalent inertia calculated under a single small disturbance has a certain random error, a dynamic aggregation strategy that takes into account the evaluation results of multiple disturbance events is proposed, and an evaluation method for node equivalent inertia distribution applicable to the new power system is formed. Finally, the effectiveness of the proposed method is verified by taking the IEEE 39-bus system and a certain provincial power grid in China as cases. The results show that the proposed method requires a small amount of data, and only the frequency measurement data collected by the synchrophasor measurement unit at each node is needed to realize the effective evaluation of grid inertia distribution, and the evaluation results have high accuracy and strong timeliness.

      • TAO Yukun, YANG Feifei, HE Ping, LI Congshan, JI Yuqi

        2024,48(13):60-68, DOI: 10.7500/AEPS20230603001

        Abstract:The active frequency response capability of wind turbines has become a prerequisite for the wind power integration in the future, but the improper switching of control strategies between the frequency support stage and the speed recovery stage may cause a secondary frequency drop (SFD). Aiming at this problem, this paper proposes a flexible frequency response strategy for wind turbines. Firstly, the nonlinear model of wind turbines is linearized at the initial operation point, and the impact of the initial operation point on the output characteristics of wind turbines is analyzed. Secondly, based on the linearized model of wind turbines, the frequency response transfer function for the power system composed of wind power and thermal power is derived, and the impact of system parameters on the dynamic characteristics of frequency response is studied. Then, the contradiction between SFD and rotational speed recovery is studied, and a participation factor of auxiliary power is constructed by using piecewise function and Logistic function. The electromagnetic power output of the wind turbine is adjusted through shape coefficients. Finally, the comparative simulation study is conducted on the MATLAB/Simulink platform. Simulation results show that the proposed strategy can eliminate the SFD while guaranteeing a satisfactory rotational speed recovery.

      • YU Jingxing, HUANG Jiyu, ZHANG Yongjun, ZHONG Kanghua

        2024,48(13):69-78, DOI: 10.7500/AEPS20231031007

        Abstract:The data-driven stability assessment model with the input of steady-state characteristics has an important application prospect in the safety and stability research and judgment of new power systems, but it needs to solve the problem of extracting key characteristics caused by the large number of nodes and complex network structure in the model design, and provide more abundant assessment information such as instability modes. Therefore, a set of deep learning stability assessment model based on steady-state information input is designed for prediction of the leading instable generators of large-scale power grid. Firstly, a dynamic pooling dimensionality reduction model of heterogeneous graphs and node characteristics is proposed, which can dynamically merge nodes according to the similarity of node characteristics during the characteristic aggregation process to achieve parallel dimensionality reduction of large-scale power grid topology, node number and characteristics. Secondly, a generator-specified classifier model for the leading instable generators is proposed. Through global attention aggregation, the relative motion information of generators of the whole network is integrated into each generator characteristic vector, so that the identification model of leading instable generators can cope with the number of generator in structure and has good generalization ability. Finally, the model is verified in the actual large-scale power grid, and the effect and application performance of the key links are visually analyzed.

      • ZHANG Ziqi, CHEN Zhong

        2024,48(13):79-88, DOI: 10.7500/AEPS20230907004

        Abstract:In the context of energy transition, large-scale distributed photovoltaic (PV), energy storage systems and interactive loads are integrated into the distribution network. In dispatching and optimization models, due to differences in resource characteristics, various entities, such as distribution networks and end-users, possess the potential to act as flexible control variables or may still exhibit randomness. These entities may demonstrate flexibility when their load interaction capabilities are strong, energy storage capacities are high, and prediction errors are low; conversely, they may exhibit uncertainty. Firstly, this paper investigates transformation mechanisms of flexibility and uncertainty and derives general transformation conditions between control variables and parameters of various entities based on robust optimization results with aggregated power. Secondly, considering the optimal controllable or uncertain range of power aggregation under temporal coupling, a two-stage robust optimization approach is employed to delineate the controllable range of control variables and the uncertain interval of parameters. Finally, case studies are conducted to validate the effectiveness of the transformation conditions and characterization methods, which provides support for the modeling and rapid solving of multi-level coordinated optimization problems in the power grid.

      • SHI Qinlin, TANG Bo, YU Guangzheng, ZHANG Yu, WANG Haojing, LAI Xin

        2024,48(13):89-99, DOI: 10.7500/AEPS20230621001

        Abstract:Distributed generators and flexible adjustable loads are widely integrated into the distribution network, making their source-load characteristics and supply-demand relationships increasingly complex. Distributed energy storage systems (DESS) play an important role in optimizing the operation characteristics of active distribution networks. A distributed energy storage sequence planning method based on priority index is proposed to address the problem of unclear actual grid structure and strong DESS functional complexity in the process of power grid planning, which makes it difficult to achieve global optimization due to a single planning scenario. This method characterizes the comprehensive energy storage configuration demand from the perspective of demand hierarchy analysis, guiding the optimization configuration and orderly integration of energy storage. Firstly, a priority index construction method based on user demand analysis of distribution network is proposed to determine the priority of each user integrating into DESS. Secondly, taking into account the uncertainty of wind and photovoltaic output, a multi-objective planning model for distributed energy storage based on sequence optimization is proposed to determine the access location and capacity of DESS in the grid distribution network. Finally, an evaluation system for the improvement of user energy storage demand is established, providing theoretical support for the formulation of energy storage planning schemes. The simulation of a certain actual power supply grid is selected to verify that the proposed method and model can promote the accommodation of renewable energy resources and effectively guide the layout planning of energy storage in distribution networks with high-proportion renewable energy resources.

      • HUANG Manyun, XU Qiying, SUN Guoqiang, WEI Zhinong, SUN Kang

        2024,48(13):100-108, DOI: 10.7500/AEPS20231106005

        Abstract:With the development of advanced metering infrastructure and the wide application of smart meters, the rich terminal measurement information is provided for the three-phase state estimation of distribution networks. At the same time, a large amount of smart meter data puts forward higher communication bandwidth and real-time storage requirements to the communication system of distribution networks. In order to alleviate the phenomenon of the measurement congestion and delay, this paper introduces an event-triggered mechanism instead of the traditional periodic sampling of measurement data, which ensures the timely uploading of effective measurement information while reducing the communication cost and investment. On this basis, for the real-time state sensing problem of distribution network, this paper proposes a three-phase dynamic state estimation method based on the robust ensemble Kalman filter, which can maintain estimation accuracy similar to the weighted least squares method in normal operation scenarios. The method also possesses strong robustness against bad data.

      • DONG Xiaohong, KONG Huazhi, DING Fei, WANG Mingshen, YU Xiaodan, MU Yunfei

        2024,48(13):109-119, DOI: 10.7500/AEPS20230421001

        Abstract:As the market share of electric vehicles continues to grow annually, the proportion of electric vehicle charging load limited by the capacity of power battery in the region to the total electricity load continues to increase. To this end, this paper proposes a medium- and long-term charging load forecasting method for electric vehicles considering battery aging. First, a total capacity forecasting model for electric vehicle batteries in the rigion considering battery aging is constructed to forecast the total capacity attenuation caused by battery aging, as well as the total capacity increase caused by the replacement with new batteries and the growth in the number of the vehicles. Then, an estimation model for the aging characteristics of power batteries considering temperature changes is constructed to estimate the maximum capacity, rechargeable capacity and driving range of the battery after each charging cycle. When the maximum capacity of the battery is insufficient to ensure the safe operation of the vehicle, it is replaced with a new one. Finally, a vehicle behavior simulation model considering charging costs is constructed to simulate both vehicle travel and charging processes. By using the fuzzy C-means method to partition different kinds of charging loads of electric vehicles, the medium- and long-term loads of electric vehicles in the region are determined through Monte Carlo simulation and linear weighting. The simulation results show that as the vehicle usage time increases, the fluctuation degree of the annual load curve continues to increase. Compared with new vehicles, after battery aging, the peak time of weekly electricity load of single vehicle will be earlier, and the peak-to-valley differences of loads will also increase.

      • QIE Dan, WAN Haiyang, ZHANG Tongfei, SUN Xiaoguang, WANG Zhiqiang, LIU Wenxia

        2024,48(13):120-129, DOI: 10.7500/AEPS20230908002

        Abstract:In order to improve the coordination and robustness of pre-disaster and post-disaster power repair materials and repair crew scheduling, a pre-disaster pre-layout and post-disaster collaborative scheduling strategy for power repair materials considering the dual uncertainties of fault information and material demand is proposed. Firstly, in view of the dual uncertainties of pre-disaster forecasting information and power repair material, considering the degree of risk preference of decision makers, a distributed robust optimization (DRO) model of two-layer material allocation distribution based on the mean-conditional value-at-risk (CVaR) is established. The upper layer optimizes the selection of material transfer points and the number of preset power repair materials with the goal of minimizing the cost of power repair material allocation. The lower layer searches for the worst fault scenario distribution based on the mean-CVaR tool, and robust optimizes the power repair material allocation strategy from the transfer point to the fault point in the fault scenario to obtain the fault loss cost. Secondly, considering the post-disaster time series coupling constraints of material and repair crew scheduling, a mixed-integer linear programming model is established with the goal of minimizing the outage loss, the type and number of materials allocate to each fault point from the transfer point and the repair crew scheduling as decision variables. Finally, through the simulation analysis of the actual 118-bus distribution network, the effectiveness of the proposed strategy is verified.

      • >Application Research
      • ZHAN Ling, HU Bin, WANG Yaoxin, NIAN Heng

        2024,48(13):130-137, DOI: 10.7500/AEPS20230717007

        Abstract:The increasing penetration of power electronic devices in power grids has led to a decrease in grid strength and inertia, and the transient synchronization stability problem under grid faults is becoming more and more prominent. To address the transient loss problem of grid-connected inverters during weak grid faults, a transient synchronization model for grid-connected inverters is developed considering the phase-locked loop damping and the initial angular velocity at the moment of fault occurrence. The influence law of variations in phase-locked loop damping and initial angular velocity on transient synchronization stability is analyzed. Furthermore, an additional damping control method of phase-locked loop based on the feedback correction of frequency deviation is proposed to enhance the transient synchronization stability of grid-connected inverters. To address the transient loss problem posed by serious grid faults without stable equilibrium points, a dynamic compensation method for output angular velocity of phase-locked loop is proposed to achieve the stable operation of the system after fault recovery. Finally, a hardware-in-the-loop experimental platform is constructed to verify the theoretical analysis and control methods.

      • ZHENG Jian, LI Xialin, GUO Li, LIU Hongyan, HUANG Yuhui, PANG Xiulan, LI Xiaofeng

        2024,48(13):138-146, DOI: 10.7500/AEPS20230608002

        Abstract:When the high proportion of converters are connected to the weak grid, it is easy to produce the low-frequency dynamic phenomenon dominated by the interaction influence of “outer loop control-phase-locked loop (PLL)-weak-grid”. Because of technical security and other reasons, it is difficult to completely obtain the line parameters and converter control parameters on the network side, which makes it difficult to construct the low-frequency dynamic stability analysis model. Therefore, a data-driven parameter identification method for low-frequency dynamic stability analysis model is proposed. Firstly, the network parameter matrix is identified by the least square regression algorithm. Secondly, the system matrix is established, and the dynamic mode decomposition algorithm based on singular value decomposition is used to reconstruct it and replace it with the corresponding control link. By solving a set of linear equations, the control parameters of the outer loop and PLL of all converters can be obtained simultaneously. Then, combined with the device-side model, the complete small signal stability analysis model of a system is constructed. Finally, a case with two renewable energy stations connecting to the system is built in PSCAD/EMTDC to verify the accuracy of parameter identification and the effectiveness of the model, and to further analyze the low-frequency dynamic stability of the system.

      • WANG Juanjuan, WANG Zehao, LIU Yuekun, FENG Junjie, FU Chuang

        2024,48(13):147-159, DOI: 10.7500/AEPS20230728002

        Abstract:The modeling and stability analysis of modular multilevel converter (MMC) under symmetric conditions has received extensive attention. In practical engineering, MMC might be in asymmetric conditions, such as asymmetric inductance of the bridge arm and asymmetric voltage on the AC side. The admittance modeling and stability analysis under asymmetric conditions need to be further studied. At present, considering the admittance model of the system with multi-frequency coupling and the quantitative admittance dimensionality reduction methods are the difficulties in the stability analysis of asymmetric conditions. Therefore, this paper mainly establishes the MMC admittance model suitable for asymmetric conditions, and studies the matrix dimensionality reduction method suitable for small disturbance stability analysis under MMC asymmetric conditions. The dimensionality reduction method is based on the vector norm of admittance matrix. It is suitable for “black box” system and various asymmetric conditions, and can quantitatively evaluate the dimensionality reduction error of the admittance matrix with each order. Taking the Guangxi-side model of Luxi back-to-back asynchronous grid-connection project of China as a case, PSCAD/EMTDC electromagnetic transient simulation is used to verify the accuracy of the proposed model and the applicability of the proposed dimensionality reduction method under various asymmetric conditions.

      • SONG Guobing, YANG Jiayi, CHANG Zhongxue, ZHANG Chenhao, XU Ruidong

        2024,48(13):160-170, DOI: 10.7500/AEPS20220929015

        Abstract:The transformation of converter technology has led to the weakening or even cancellation of passive components at the line boundary, making it difficult to achieve fault identification across the full line length based solely on the single-end electrical characteristics. In response to this issue, this paper fully utilizes the high controllability of the converter, actively constructs specific response characteristics of the converter to internal and external faults, establishes active boundaries that cooperate with single-end quantity protection, and thus achieves fault identification across the full line length at a single end. On this basis, further discussion is conducted on the additional control strategies for active boundary characteristics and the selection criteria for key parameters. The propagation law of active boundary response in fault circuits is analyzed, and a single-end full-line high speed protection criterion is designed to match it. The simulation verification results show that the proposed method can still reliably identify high-resistance faults, improving the reliability and sensitivity of traditional single-end protection.

      • LI Xiaobo, ZHANG Shile, PENG Chaohong

        2024,48(13):171-183, DOI: 10.7500/AEPS20230922007

        Abstract:In flexible grounded systems, single-phase grounding protection based on steady-state fault characteristics generally has low resistance to transition resistance, and this problem is further exacerbated after the connection of parallel small resistors. This paper studies the relationship between the ratio of the transient DC component in the low-frequency transient zero-sequence current of faulty and non-faulty lines after the connection of parallel small resistors, and finds that the transient DC component ratio is only related to the capacitance to ground. The relationship between the ratio of low-frequency transient zero-sequence current distortion rates of faulty and non-faulty lines is analyzed, and a method for line fault selection based on low-frequency transient zero-sequence current distortion rates in flexible grounded systems with high-resistance grounding faults is further proposed. Fault line selection is achieved by comparing the magnitude of low-frequency transient zero-sequence current distortion rates of each feeder within a specific time window, and busbar faults and outgoing line faults can be accurately distinguished. This method can avoid the impact of zero-sequence voltage transformer disconnection and zero-sequence current transformer polarity reversal, and is less affected by fault distance. At the same time, this method uses transient fault characteristics to form a line selection criterion, which is beneficial for overcoming the weak steady-state fault component after connection of parallel small resistors, and has low requirements for instrumental transformer accuracy. Finally, the accuracy and effectiveness of the method are verified through real-time digital simulation and experimental platforms.