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      • HOU Jinming, SUN Wei, XIAO Jinyu, JIN Chen, DU Ershun, HUANG Jie

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210223001

        Abstract:The technology progress plays an important role in supporting the low-carbon transition of power systems. At the same time, the development of technology should also aim at the realization of the low-carbon transition of power systems. Especially in long term, the mutual interaction between them is more significant. China proposes to achieve carbon neutrality before 2060, and the power system will gradually achieve low-carbon or even zero carbon emissions. The development level of key technologies such as clean energy power generation, ultra-high voltage (UHV) power transmission and energy storage has become an important factor in the economic feasibility of power system transition, and the development of the key technologies should also be accelerated with the goal of carbon neutrality. In order to quantitatively evaluate the coupling and matching relationship between the key technology progress and the economical feasibility of the low-carbon transition of power systems, a framework and a method of collaborative optimization of them are proposed. It combines the technology maturity analysis and cost forecast with the power system expansion planning model, and takes the 2060 long-term power planning of China as a case to study the clean low-carbon transition of power system in different technology development scenarios, and the contribution of different technologies to the reduction of the overall unit electricity cost of the whole system is analyzed.

      • WANG Yushan, DENG Hui, WANG Xu, JIANG Chuanwen, FANG Le, MA Junchao

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210702006

        Abstract:Aiming at the problem that the distribution network cannot guarantee the safe and reliable power consumption during the typhoon extreme disasters, a robust optimization of configuration and operation strategy of mobile energy storage in the distribution network based on scenario probability is proposed to raise the distribution system resilience considering the influence of spatial-temporal evolution of typhoon on the line fault status of distribution networks. Firstly, after the geographical area of distribution networks is gridded, the mapping coordinate system is built. The spatial-temporal evolution model of typhoon disaster is established based on the meteorological information, and then the spatial-temporal characteristic matrix of the distribution line failure rate is established. Secondly, based on the spatial-temporal characteristic probability matrix of line failure, the vulnerable line is determined, and the robust optimization is used to find the optimal configuration and operation strategy of mobile energy storage in the probability scenario to minimize the economic loss of the disaster-affected distribution network during the typhoon disaster. A three-layer robust optimization model is established for the optimal configuration and operation of mobile energy storage, and the flexibility of mobile energy storage is fully used to provide the phased power support for the distribution network during the typhoon disaster. Finally, the improved IEEE 33-bus distribution network is used for case analysis and the applicability of the proposed optimal strategy is illustrated.

      • QIN Huaqin, LIANG Ye, QIAN Qi, GUO Sijia, MA Xianqin, GUO Chonghui

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210616001

        Abstract:From the perspective of fluctuation patterns of user data for electricity theft,a detection method of electricity theft behavior based on retrieval of typical electricity theft users" similarity is proposed. Firstly, dynamic time warping is used to measure the similarity of consumption data for electricity theft users, and the similarity matrix of electricity theft is obtained. Secondly, combining with the similarity matrix of electricity theft, the affinity propagation clustering method is used to classify electricity theft users, so as to realize automatic clustering of electricity theft users, and the cluster center is used as typical electricity theft user. Finally, the similarity of typical electricity theft users in the electricity database is used to retrieve the users who have similar electricity consumption behaviors to the typical electricity theft users, and the suspected electricity theft users are identified based on manual experience analysis. The feasibility and applicability of the proposed method are verified by an example analysis of the data provided by Electric Power Company of State Grid of a province in China.

      • HOU Hui, ZHU Shaohua, YU Jufang, LI Xianqiang, WEI Ruizeng, HUANG Yong

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210317005

        Abstract:Wind disaster may lead to large-scale power failure in distribution networks. Effective prediction of user number in power outage for distribution network can provide auxiliary guidance for emergency repair. This paper proposes a prediction model for user number in power outage for distribution network under high-efficient data dimensionality reduction. First, based on the data-driven method and considering all characteristic variables i.e., global variables, a prediction model for user number in power outage for distribution network based on random forest algorithm is constructed. Then, the relationship between various characteristic variables and response variables affecting power outage users of distribution network during typhoon is analyzed in detail by using partial dependence plots. And the characteristic dimension is reduced, the secondary modeling forms a more efficient prediction model for user number in power outage for distribution network after dimensionality reduction. Compared with the prediction model considering global variables, the prediction model for user number in power outage for distribution network after characteristic dimensionality reduction reduces the burden of data collection to a certain extent, improves the calculation efficiency, and provides an effective basis for power grid disaster prevention and reduction.

      • HUO Chengxiang, YU Dahai, MA Xiaoguang, XIA Chao, LI Zhiqiang, GAO Lei

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210705004

        Abstract:Because the dynamic gain of excitation systems has a significant impact on the dynamic stability of salient-pole generators, it is often necessary to adjust the dynamic gain and then configure the power system stabilizer (PSS) in order to improve the damping of power system. However, there are some fuzzy understandings about the impact of dynamic gain on the dynamic stability of generators. Firstly, the impact of dynamic gain of excitation systems on the dynamic damping is analyzed. Then, the impact of dynamic gain of excitation systems on the damping torque, damping ratio of salient-pole generators and the frequency response characteristics of excitation systems is calculated and analyzed with typical unit parameters and operation conditions. The simulation is carried out in single-machine infinite system, two-machine system and real system. The calculated results are in agreement with the simulation results. Finally, the experiments are carried out in the network source coordination laboratory and the engineering field, and the correctness of the simulation and calculation results is verified, that is, the larger the dynamic gain of excitation system is, the weaker the dynamic damping of salient-pole generator is. In order to improve the dynamic damping of salient-pole generators (such as hydrogenerator), the dynamic excitation gain should be smaller on the premise of meeting the requirements of relevant standards, and the system damping should be further improved by configuring corresponding PSS.

      • JIA Xueyong, DONG Xiaoming, SUN Hongwen, WANG Yasong, CHEN Fan

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210702009

        Abstract:Aiming at the influence of meteorological and geographic factors on power transmission characteristics of power grids, an effective analysis model and algorithm are proposed. Firstly, the heat balance equation of the transmission line is combined with the conventional power flow equation, and the meteorological and geographic information around the overhead transmission line is introduced into the power flow calculation as variables. The extended Jacobian matrix and Newton iterative format are derived, and an electric and thermal coupling unified power flow model and its solution algorithm considering environmental factors are established. Secondly, the influence degree of the difference of wind speed, altitude and environment temperature on line resistance, temperature, active power and reactive power loss is comparatively analyzed. The case studies show that environmental factors affect the electric and thermal balance of overhead conductors and change the line resistance, which has a significant influence on the power flow distribution, active and reactive power losses. Based on the temperature data of 14 locations in Xinjiang Uygur Autonomous Region, China, the temporal and spatial correlation characteristics of daily average temperature at different locations are measured by Pearson correlation coefficient, and the changes and differences of power transmission characteristics of power grids in different seasons are analyzed. Finally, based on the extended Jacobian matrix of the improved power flow model, a V-Q sensitivity analysis method considering environmental factors is proposed, and compared and analyzed with the traditional model in different scenarios. The results show that the traditional model neglects the influence of the line temperature and resistance on the electrothermal balance, which leads to some errors due to the change of environmental factors. Moreover, this error has a tendency to further expand under heavy load conditions, and the improved model will effectively reduce the errors.

      • PENG Jiawei, PAN Shuguo, GAO Wang, SHEN Jian, ZHANG Min

        Available online:January 25, 2022  DOI: 10.7500/AEPS20210207003

        Abstract:With the continuous development of power electronized power grid, the increasingly wide-band and complex power grid signals require higher adaptability and accuracy of measurement algorithm. Therefore, an adaptive measurement method for wide-band signals based on windowed interpolation and multiple modulation zoom spectrum analysis is proposed. After selecting the window function based on the main and side lobe characteristics and interpolation correction process, according to the main-lobe jamming of the signal spectrum, double-spectral-line interpolation algorithm based on four-term fifth-order Nuttall window and multiple modulation zoom spectrum analysis are separately used for targeted measurements. Finally, the measurement accuracy and stability of the proposed method are verified by simulation comparison and measured data analysis. The results show that the high-accuracy adaptive measurement of harmonics and inter-harmonics with similar frequencies in the range of 0~2.5 kHz is effectively realized. Higher measurement accuracy and lower computation cost enable it to meet the measurement requirements of power electronized power grid.

      • SUN Dayan, GUAN Li, HUANG Guodong, LUO Zhiqiang, HU Chenxu, CHANG Jiang

        Available online:January 25, 2022  DOI: 10.7500/AEPS20211023003

        Abstract:The proportion of renewable energy installed capacity is increasing rapidly, and the task of accommodation is arduous. Trans-regional and cross-provincial market-oriented transactions have played an important role in promoting the large-scale accommodation of renewable energy. For the trans-regional and cross-provincial electricity spot trading for surplus renewable energy organized by State Grid Corporation of China, the paper summarizes the basic framework of spot trading, and outlines the trading mechanism from the aspects of organizational process and market connection. According to the actual operation situation in the past four years, the annual, monthly, and daily transactions are comprehensively summarized from the perspective of electric power and price, and an evaluation index system is established to analyze its positive role in promoting the accommodation of renewable energy and forming the time-of-use electricity price. Combined with construction objectives of the new power system and development requirements of the electricity market, the limitations of trans-regional and cross-provincial electricity spot trading for surplus renewable energy in terms of transaction scope, transaction mechanism and participating entities are analyzed, and the relevant suggestions for the future construction of cross-provincial electricity spot market are put forward.

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      Volume 46,2022 Issue 2

        >Application of Blockchain Technology in Power Systems
      • YAN Yong, CHEN Xingying, WEN Fushuan, GUO Shaoyong

        2022,46(2):1-14, DOI: 10.7500/AEPS20210131001

        Abstract:In recent years, blockchain technology has developed rapidly, and has been applied to the energy industry at home and abroad. However, practitioners in the energy industry have different understandings on blockchain, and there are many controversies such as the necessity of applying blockchain in the Energy Internet. Through the in-depth analysis of the blockchain, the basic concepts and research framework of the energy blockchain are proposed, so as to form a more systematic theory and application system, and provide ideas and references for potential practical applications. Firstly, this paper analyzes the development trend and dilemma of Energy Internet, and expounds the concept and application value of blockchain. Then, by comparing the characteristics of Energy Internet and blockchain, this paper puts forward the definition and connotation of energy blockchain. Then, this paper analyzes the application of energy blockchain, puts forward the research framework of energy blockchain, and expounds the common key technologies of energy blockchain. Finally, the development path of energy blockchain is given.

      • ZHANG Wei, LU Xiang

        2022,46(2):15-23, DOI: 10.7500/AEPS20210304002

        Abstract:The sharing mode based energy storage trading mode can effectively reduce the investment cost and usage cost, and the characteristics of decentralization and trustlessness that it relies on are consistent with the trading characteristics of blockchain. A trading model of the energy storage aggregator with combined energy-storage-shared and energy-self-operated mode is proposed with peer-to-peer trade. All the trade matchings among users are carried out through smart contracts, and both energy storage leasing and energy purchase/sale are carried out in a single trading cycle, so as to shorten the trading cycle of users on the chain. In addition, the default penalty model and the default compensation model are established respectively for the default behavior of on-chain users. Finally, the simulation results based on Remix and MATLAB show that the trading model is feasible and effective in improving the convenience and economy.

      • >Basic Research
      • CHEN Changming, ZHANG Qun, HUANG Yixin, WANG Xin, WANG Decheng, YANG Li, LIN Zhenzhi

        2022,46(2):24-32, DOI: 10.7500/AEPS20210309007

        Abstract:Park-level integrated energy system (PIES) is one of the typical applications of multiple energy coupling and supply on user side, whose optimal configuration is of great significance to improve the configuration economy and energy efficiency of PIES. In this context, an optimal configuration method of PIES considering optimal construction time sequence and cloud energy storage is proposed. First, an overview of the mechanism for cloud energy storage and the structure of PIES with cloud energy storage are given, and the set of PIES construction time sequences is analyzed. And then, a bi-level optimal configuration model of PIES considering the optimal construction time sequence and the cloud energy storage is constructed. In the proposed bi-level model, the optimal configuration strategy of PIES is formulated in the upper layer and passed to the lower layer. The optimal scheduling strategy of PIES is obtained in the lower layer according to the optimal configuration strategy of PIES, and the total operation cost of PIES is fed back to the upper layer. Then, the Karush-Kuhn-Tucker (KKT) condition and big-M method are utilized to transform the bi-level optimal configuration model into a single-layer mixed-integer linear programming model, which can be easily solved by the Gurobi solver. Finally, the case studies verify that the proposed model can improve the configuration economy and the equipment utilization of PIES.

      • XU Chaoran, XU Xiaoyuan, YAN Zheng, LI Hengjie

        2022,46(2):33-42, DOI: 10.7500/AEPS20210413003

        Abstract:A power system dispatch method based on data-driven distributionally robust optimization (DRO) is proposed to deal with the operation problem of power system considering the uncertainty of wind power. Firstly, the statistical information of wind power data is mined, and a construction method of probability distribution ambiguity set for wind power based on principal component analysis and kernel density estimation is proposed to describe the randomness of wind power and the spatial correlation between the outputs of different wind turbines. Secondly, aiming at the dispatch problem with wind power, a two-stage DRO problem considering probability distribution ambiguity set is established. Thirdly, the DRO problem is transformed into its equivalent solvable form, and the affine strategy and duality principle are used to transform it into a linear programming problem for solving. The range parameter selection strategy of probability distribution ambiguity set based on out-of-sample test is proposed to ensure the reliability and economy of the dispatch scheme. Finally, the 6-bus and IEEE 118-bus systems are used for simulation analysis, and the proposed DRO method is compared with the DRO method without consideration of the correlation of random variables and the traditional stochastic and robust optimization methods to verify the effectiveness of proposed method.

      • XU Xun, XIE Lirong, YE Lin, LU Peng, LIANG Wuxing

        2022,46(2):43-55, DOI: 10.7500/AEPS20201104010

        Abstract:In order to effectively solve the unit commitment problem caused by the uncertainty of wind power output, based on the nonparametric kernel density estimation of probability density distribution for the wind power prediction error, a bi-level optimization model of day-ahead and real-time stages is proposed. Firstly, based on the probability density distribution of the wind power prediction error, the up and down fluctuation domain of wind power is constructed. Secondly, a bi-level optimization model for nonparametric kernel density estimation of the optimal confidence level of the wind power is established. The upper layer takes the minimum cost of wind power-thermal power cooperative operation as the goal, and the lower layer takes the minimum control deviation of output power for wind power and thermal power as the goal. The model is solved by the CPLEX solver. Finally, in the modified IEEE 30-bus and modified IEEE 118-bus systems, actual data from a wind farm in Xinjiang, China is used for verification. The experimental results show that the proposed model can reduce the system operation cost, and coordinate the real-time output power of wind power and thermal power, as well as restrain the fluctuation of active power in the wind farm.

      • JI Xingquan, HAO Qing, ZHANG Yumin, HAN Xueshan, YANG Ming, ZHANG Xuan

        2022,46(2):56-64, DOI: 10.7500/AEPS20210412001

        Abstract:In order to reduce the conservatism of the robust optimization methods and the complexity of the stochastic optimization methods, and enhance the ability of power system to deal with occasional line fault disturbance, this paper proposes a distributed robust unit commitment model with N-k safety criterion under uncertain distribution. According to the limited historical sample data, under the condition of satisfying a certain confidence level, a fuzzy set containing the real N-k fault probability distribution is constructed based on imprecise Dirichlet model (IDM) to describe the uncertainty of transmission line fault probability distribution. Firstly, by identifying the worst probability distribution in the fuzzy set, the original distribution robust optimization scheduling problem is transformed into a two-stage robust optimization decision model under the deterministic probability distribution conditions. Then, the column and constraint generation (C&CG) algorithm is used to process the model, the main problem and subproblem are transformed by using Big-M method, segment linearization technique and duality principle. And a mixed-integer linear programming problem (MILP) model is obtained, which effectively reduces the difficulty in solving the model. Finally, four kinds of N-k uncertain sets are integrated, and case studies on IEEE 14-bus system and IEEE 118-bus system demonstrate the efficiency of the proposed method.

      • CHEN Fan, SHI Jie, LIU Haitao, WANG Ruichi, ZHAO Meilian, LIU Dichen

        2022,46(2):65-72, DOI: 10.7500/AEPS20210702003

        Abstract:Load redistribution (LR) attack is a special form of cyber-attack. It is of great practical significance to model the LR attack and study its influence on the power system operation. Firstly, the process of LR attack is analyzed, and the random process model of LR attack is established based on the semi-Markov chain. Secondly, the interaction process between the attacker and dispatcher under the LR attack is analyzed, and the load shedding model of the power generation and transmission system considering the LR attack is established. Then, a defense strategy for the vulnerable line based on the transmission line utilization rate is proposed from the perspective of protecting the critical measurement data, and a reliability evaluation algorithm of the power generation and transmission system considering the LR attack and defense of the vulnerable line is further proposed. Finally, the modified IEEE 14-bus system is taken as an example to verify correctness of the proposed reliability evaluation algorithm of the power generation and transmission system considering the LR attack and effectiveness of the defense strategy for the vulnerable line.

      • LI Baoqin, WU Junyong, QIANG Ziyue, QIN Liuyun, HAO Liangliang

        2022,46(2):73-82, DOI: 10.7500/AEPS20210402007

        Abstract:The massive measurement data lays the foundation for the data-driven transient stability prediction method. However, the inherent unbalance nature of unstable samples restricts the performance of this type of methods. In order to solve the problem of sample imbalance in transient stability prediction, a data augment method is proposed based on the improved deep convolutional generative adversarial network (DCGAN). New and effective unstable samples are generated by adversarial training of the generator and discriminator, which are used as a supplement to the original training set. In offline training, a deep belief network is used as the classifier, and the extended sample set is used for training, which effectively improves the recognition rate of the unstable samples. In online application, once the system changes unexpectedly, the offline model is updated by samples transferring and model fine-tuning technology, and after that, the unstable samples are further enhanced, which can greatly improve the transfer speed of transient stability adaptive assessment and the recognition rate of unstable samples in the new scenarios, making the evaluation results more reliable. The simulation results on IEEE 39-bus system and IEEE 140-bus system verify the effectiveness of the proposed method.

      • SUN Lixia, PENG Jiajie, BAI Jingtao, CHEN Xinling, TIAN Yiyun

        2022,46(2):83-91, DOI: 10.7500/AEPS20201129003

        Abstract:The rotor angle stability and voltage stability of power systems are the bases for the secure operation of power systems, and the stability analysis is one of the bases for the stability control strategy formulation. Considering the influence of the power grid topology on the power system transient stability, the Node2vec graph embedding algorithm is used to map the power grid topology into a low-dimensional dense matrix, and the spatial topological features of the power system are obtained, which are combined with the measurement data to form a reconstructed data set as the input of the assessment model. Considering that the various stability problems of power systems are often intertwined, a transient stability assessment model based on multi-task learning is proposed to realize the assessment of rotor angle stability and voltage stability of power system at the same time, and the instability areas in the power grid are determined and the visualization is realized. Finally, the validity of the model is verified by the New England 10-generator 39-bus system.

      • LI Guocheng, LU Jun, WANG Yun, HUANG Rui, LIU Mouhai

        2022,46(2):92-100, DOI: 10.7500/AEPS20210323005

        Abstract:With the rapid development of smart grids, the electricity theft methods are diversified, and the electricity theft data also has the characteristics of having difficulty in labeling and classing unbalanced in samples. Aiming at the problem of electricity theft detection where the electricity theft data is unlabeled and class unbalanced, an electricity theft detection algorithm of isolation forest based on Bagging secondary weighted ensemble is proposed. Firstly, by analyzing the electricity theft patterns of residents and commercial users, based on the minimum similarity criterion between isolated classes, the isolated feature sequence of various electricity theft patterns is optimized and the corresponding isolation forest model is trained. Secondly, the weighted voting method is used to obtain the secondary ensemble isolation forest model to realize the electricity theft detection under the condition of unbalanced distribution of electricity theft modes. Seven commonly used learning algorithms and Bagging heterogeneous ensemble learning algorithms are compared. Simulation experiment results show that the isolated feature sequence optimization strategy of the proposed algorithm can effectively improve the electricity theft detection effect under the condition of unlabeled and class unbalanced, and the secondary weighted ensemble strategy can also improve the electricity theft detection effect under the condition of unbalanced distribution of electricity theft modes.

      • YANG Dongfeng, FU Qiang, LIU Xiaojun, LIU Yingying, JIANG Chao

        2022,46(2):101-108, DOI: 10.7500/AEPS20210524011

        Abstract:In order to achieve accurate identification of distribution network topology and line parameters, a joint online identification method for topology and line parameters of distribution network based on smart meter measurement data is proposed considering the change of topology. Firstly, a support vector machine (SVM) based multi-classification model and a linear regression based initial model for topology and line parameter identification are established using historical measurement data of different topologies. Then, the SVM multi-classification model is used to realize the mapping between online measurement data and topology structure to obtain the initial values of topology and line parameters, and the topology and line parameter identification correction model is combined to obtain accurate identification results. In addition, to improve the numerical stability, orthogonal matrix and right triangular matrix decomposition is used to solve the linear equations in the identification process. Finally, the effectiveness of the method is verified by arithmetic simulation.

      • LIN Lijuan, JIA Qingquan, TIAN Shuya, LIANG Jifeng, LI Tiecheng, CHENG Ziwei

        2022,46(2):109-117, DOI: 10.7500/AEPS20210209001

        Abstract:The high proportion of renewable energy and power electronic equipment connected to the distribution network has led to densification, decentralization and wide distribution of harmonic sources. It is obviously that the traditional point-to-point harmonic mitigation method is not applicable. By taking the voltage detection based active power filter (VDAPF) as the mitigation equipment, this paper proposes a distributed mitigation scheme combining centralized and distributed control of multiple VDAPFs on the grid side. To obtain the overall optimal voltage distortion at observation nodes, a long time-scale optimal model for centralized control of operation points of distributed mitigation system at the whole network level is established, and the control instruction provides the global mitigation reference. At the same time, for the problems of frequent communication and large amount of calculation on a short time scale in the centralized optimal control for local operation parameters of VDAPF, this paper proposes a distributed setting method for local parameters of VDAPF oriented to mitigation partition. The local operation control parameter of each order of harmonic is set separately based on the consistency algorithm. The case study results show that the proposed distributed mitigation scheme can coordinately control harmonic voltages of the whole network, and the distributed optimization method improves the calculation efficiency of local operation parameters and has good scalability, reliability and robustness.

      • KONG Minyue, SUN Dan, NIAN Heng

        2022,46(2):118-125, DOI: 10.7500/AEPS20210308003

        Abstract:In order to analyze the grid-connected characteristics of doubly-fed induction generator (DFIG) based wind turbines, it is extremely important to establish an accurate model of the power response characteristics at the grid-connected point. A modeling method is proposed to solve the modeling problem of the power characteristics of DFIG-based wind turbines at the grid-connected point. First, aiming at the vector control and virtual synchronous generator control in the DFIG-based wind turbine system, power response characteristic models are established and analyzed separately. Then, based on the power response data at the grid-connected point obtained by applying the power disturbance command to the DFIG-based wind turbine, the optimal adjustment method of the damping factor in the damping least square method is proposed, and the model is identified based on the improved method to realize the fitting of the power response characteristics at the grid-connected point. Moreover, the influence of generator parameters of DFIG-based wind turbines on model fitting error is analyzed, whose influence degree through parameter trajectory sensitivity calculation is analyzed, and combined with simulation, the applicable scope of the model is further clarified. Finally, simulation and experimental results verify the rationality of the built power response characteristic model and the effectiveness of the proposed modeling method.

      • XIE Songwei, XUE Yongduan, WU Weikun, XU Bingyin

        2022,46(2):126-136, DOI: 10.7500/AEPS20210123001

        Abstract:In distribution networks, the probability of the line breaking and grounding fault is high, and it may cause electric shock, fire and other accidents. The differences of transient electric quantities between single-phase line breaking and grounding fault and normal single-line grounding fault and the applicability of existing transient line selection methods are not clear. The equivalent circuit of the single-phase line breaking and grounding fault in non-solidly grounded system is established by fault boundary conditions. The characteristics of transient zero-sequence voltage/current at the moment of line breaking and grounding in the ideal scenario are preliminarily analyzed. Also, the differences of transient electric quantities between single-phase line breaking and grounding fault and normal single-line grounding fault, and the applicabilities of the line selection methods of transient current amplitude/polarity comparison and transient power direction are analyzed. The results show that there is obvious transient process at the moment of line breaking and grounding, and the transient characteristics are different from normal single-line grounding fault. However, in the selected frequency band, the transient electric quantity constraint relationships at the moment of line breaking and grounding are consistent with that of normal single-line grounding fault. The existing line selection methods are still applicable, but the sensitivity of the line selection using the transient electric quantities generated at the moment of line breaking is low. Finally, the simulation is used to verify the applicabilities of line selection methods.

      • >Application Research
      • ZHENG Tao, LYU Wenxuan

        2022,46(2):137-145, DOI: 10.7500/AEPS20201125004

        Abstract:The collaborative active fault control and primary protection scheme for flexible DC distribution networks can effectively overcome the limitations of traditional protection schemes, but its reliability is difficult to be guaranteed in extreme cases such as communication and isolation equipment failure. Thus, it is urgent to carry out the research on relevant backup protection theory. Therefore, by utilizing the fault active control of the converter, a backup protection scheme based on the polarity of the local current sudden-change is proposed. Based on the current sudden-change generated by the converter, the protections of load switches in the reverse fault direction are blocked by measuring the polarity of the sudden-change current. Then, according to the time-sequential coordination relationship, the faulty line can be isolated reliably. This scheme is independent of communication and DC circuit breakers. Through active control of the converter, fault isolation can be realized by only using load switches. Besides, an acceleration strategy for the backup protection is proposed, and its practicability is analyzed in combination with different topologies. Finally, a four-terminal flexible DC distribution network model is established in PSCAD/EMTDC. Simulation results show that the proposed scheme can realize fast and selective isolation of faulty lines only based on local information.

      • TANG Yingjie, ZHANG Zheren, XU Zheng

        2022,46(2):146-154, DOI: 10.7500/AEPS20210124001

        Abstract:To improve the simulation efficiency of the active modular multilevel converter (MMC) with enough computational accuracy, this paper proposes a full-state arm average value model appropriate for the simulation of the active MMC. Based on the dynamic averaging theory, this paper firstly deduces the average value mathematical model and the equivalent circuit model for the arms of the active MMC. Combined with the device discretized companion model, the average value models are established for the simulation of the arm in different operation states. Finally, the full-state arm average value model is obtained by the integration and simplification of circuits. This model focuses on the low-frequency dynamic commonalities of the submodules inside the arm, and can accurately reflect the overall transient characteristics of the arm. The simulation speed of this model is not affected by the number of submodules. Besides, the proposed model can also be used in the simulation of the active MMC in the blocking state. The simulation examples based on PSCAD/EMTDC verifies the validity of the proposed model.

      • XIA Jiahang, WANG Chenxin, ZHAN Ruiqi, ZHAO Chengyong, GUO Chunyi

        2022,46(2):155-162, DOI: 10.7500/AEPS20201224008

        Abstract:Commutation failures exist in traditional high voltage direct current (HVDC) transmission systems, and a large number of filters and reactive power compensation devices are needed on the AC side, which are bulky and costly. The series capacitor commutated converter can suppress the occurrence of commutation failure, but it cannot compensate a lot of reactive power; the shunt capacitor commutated converter can reduce commutation failure probability, but there are risks such as the resonant oscillation. To solve these problems, an evolutional shunt capacitor commutated converter (ESCCC) is proposed, in which a series filter inductor is added on the basis of the shunt capacitor on the AC side of the converter valve. The commutation characteristics and reactive power characteristics are analyzed, and the resonance characteristics and reactive power requirements are considered to optimize the parameters of the shunt capacitor and filter inductance. Finally, a simulation model is built in PSCAD/EMTDC for verification. The simulation results show that the steady-state harmonics on the AC and DC sides in the ESCCC can meet the requirements, and there is no need for additional filters and reactive power compensation devices on the AC side; the probability of commutation failure can be reduced in case of a fault, and the recovery characteristics after commutation failure are good.

      • LI Kefeng, XIAO Fei, LIU Jilong, GAO Shan, MAI Zhiqin

        2022,46(2):163-170, DOI: 10.7500/AEPS20210604008

        Abstract:Aiming at the problem of unbalanced voltage sharing between series-connected insulate-gate bipolar transistors (IGBTs) in the multi-level active neutral point clamped (ANPC) inverter, a voltage balancing method of series-connected IGBTs is proposed. For every single bridge of the multi-level ANPC inverter, a single-input multiple-output (SIMO) isolated power supply is applied to generate the clamping voltage which is connected to the series-connected IGBTs. Meanwhile, clamping capacitors are added at the position where the clamping voltage is applied to maintain the clamping voltage. Eventually, both dynamic and static voltage balance of the series-connected IGBTs are realized. Because the clamping capacitors are not involved in the current changing path of the inverter, the isolated power supply requires only a small amount of power to maintain the voltage stability of the clamping capacitor. The proposed method is simple and reliable with high accuracy in voltage balancing, and is easy to be implemented in engineering. On one hand, the traditional passive snubber circuits are removed, which avoids the extra loss and reduces the cost. On the other hand, the complex active closed-loop control is unneeded, so the stability problems of closed-loop control can be avoided. Finally, the proposed voltage balancing method is verified by the experiment on a prototype of ANPC five-level inverter.

      • XUE Yang, YANG Yining, LIAO Wenlong, YANG Dechang

        2022,46(2):171-179, DOI: 10.7500/AEPS20201217001

        Abstract:Due to the strong concealment of distributed photovoltaic electricity theft and the limitation of inspection resources, the number of electricity theft samples mastered by the power utility is insufficient, which limits the accuracy of electricity theft detection. Therefore, a data augmentation method for distributed photovoltaic electricity theft based on the non-linear independent components estimation (NICE) is proposed. First, the multiple inversible functions are used to map the electricity theft samples into latent variables that obey the Gaussian distribution, and they are reconstructed into new electricity theft samples by inverse transformations. Then, the three typical photovoltaic electricity theft models are proposed, and the convolutional neural network is constructed as a classifier according to the data characteristics of electricity theft samples. Finally, the effectiveness and adaptability of the proposed method are verified by a practical example and a simulation example. Simulation results show that NICE is able to take into account both the shape and distribution characteristics of the samples, and the generated electricity theft samples can significantly improve the performance of different classifiers.

      • HU Guo, YAN Yunsong, WU Hai, JIN Peng

        2022,46(2):180-187, DOI: 10.7500/AEPS20200617004

        Abstract:Emergency load shedding is an important technical means to avoid transient instability and maintain frequency stability. The conventional accurate load shedding scheme does not consider the existing fault emergency treatment mechanism and collaborative control of the distribution network itself, and only takes the distribution terminal or load control terminal as the final actuator of the main grid stability control device to implement the precise load shedding scheme. The emergency load control strategy of distribution network based on collaboration of main grid and distribution network extends deployment of the basic units of load control from high-voltage station outgoing line to medium- and low-voltage branch line of distribution network through collaborative interaction between intelligent distribution terminals and stability control devices, so as to improve load control accuracy and avoid cutting off sensitive and important users. Combined with the distributed feeder automation and low-voltage and low-frequency load shedding control on the local side of the distribution network, an intelligent distribution terminal for load control is developed to improve the integrated load management and control ability of the distribution network in different control stages, such as rapid fault removal and self-healing, emergency load shedding, automatic load shedding and splitting. The effectiveness of the proposed control method is verified by simulation examples and engineering demonstration applications.

      • >Survey
      • XU Xinzhi, DU Ershun, GAO Yi, ZHANG Ning, LI Jun

        2022,46(2):188-199, DOI: 10.7500/AEPS20201104004

        Abstract:Operation simulation and capacity planning software tools in power systems play an important role in power system planning, operation and evaluation. In recent years, with the large-scale integration of renewable energy, the research results of models and methods for operation simulation and capacity planning are emerging one after another, and the corresponding software tools have also ushered in significant progress and updates. This paper summarizes a variety of mainstream software tools for operation simulation and capacity planning at home and abroad, and focuses on analyzing the characteristics of various software tools including general structure, temporal resolution, power flow models, unit commitment constraints, solving algorithms, etc. In addition, combined with the current research status and the development trend of the power system, related thoughts of the future operation simulation and capacity planning tools in the power system are proposed.