• Competent Authorities: State Grid Jiangsu Electric Power Co.,Ltd.
  • Sponsor: State Grid Jiangsu Electric Power Co., Ltd. Jiangsu Society for Electrical Engineering
  • Publisher: Editorial Department of Electric Power Engineering Technology
  • Add: No.1 Power Road, Jiangning District, Nanjing, China
  • Zip Code: 211103
  • ISSN  2096-320
  • CN 32-1866/TM
  • CODEN DGJIAA
  • Web Site: www.epet-info.com
  • Tel: 025-86556860 025-86558772
    025-86558553 025-86558020
  • E-Mail: epet@ijournals.cn
    epet-editor@ijournals.cn
  • Start time: 1982
  • Distributed by: Nanjing Municipal Postal Administration
  • Subscription Code: 28-305
  • Subscription: Post Offices Across China
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    • Electric power engineering technology(EPET)
    • Volume 41,2022 Issue 4
    • Publication date:

    Electric power engineering technology (EPET), with the international standard serial number of ISSN 2096-3203 and China publishing license serial number of CN 32-1866/TM, is an open accessed and bimonthly published journal since 1982. The journal has been listed as Chinese Core Journal by a guide to the core journals of China. EPET is currently indexed by Chinese Scientific and Technical Papers and Citations Database (CSTPCD) and Japan Science and Technology Agency (JST). In 2020, EPET was rated as 'RCCSE Chinese quasi core academic journal (A)' in the research report on Chinese academic journals evaluation. The discipline rank of EPET in electrical engineering was top 30% by Chinese scientific and technical citation report in 2021. The annual report for Chinese academic journal impact factors by CNKI in 2021 ranked EPET at top 10% in the field of electrical engineering by clout index (CI).

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        Oscillation Stability of New Type Power System Grid-connected with Renewable Energy
      • YUAN Chang, QIU Junqing, DAI Dumeng

        Abstract:

        Electric spring (ES) can suppress the voltage fluctuation caused by large-scale grid-connected renewable energy sources. However, ES can only work within a certain range of gird voltage fluctuations. This means, if the grid voltage fluctuates greatly, the ES will expose to the risk of off-limit failure. Focusing on this problem, the steady-state operating range and the failure mechanism of ES are analyzed. Then the influence of changes in critical load target voltage on the operating range of ES is analyzed. After that, a calculation method for critical load target voltage based on a two-port impedance model of ES is proposed, which can expand the operation range of the ES through optimal adjustment of the critical load target voltage effectively. Finally, a simulation model of the three-phase ES is built, and the detailed simulation results verify the validity of the proposed method.

      • HUANG Yunhui, WANG Lingyun, YU Hengning, WANG Dong, ZHU Guorong, HUANG Yunhong

        Abstract:

        With large-scale wind turbines connected to the power system, the power grid strength becomes weak, leading to unstability problem of wind turbines in DC voltage control timescale. The stability limit of double-fed induction generator (DFIG) system connected to weak AC grid is studied in this paper. Firstly, the relationship between the active power and terminal voltage of DFIG injected into the power grid and the current of the dq axes of the rotor as well as the physical constraints of the stability limit are studied, and the sensitivity is analyzed. The sensitivity of active power to rotor d-axis current is summarized. Then, a small-signal model of DFIG connected to weak grid is built. Through the eigenvalue analysis, the influence of the dynamic behavior of the control loop of DFIG on its stability limit is studied. The results show that the stability limit can be increased by decreasing the bandwidth of the phase locked loop (PLL) or increasing the bandwidth of the terminal voltage control loop with equal damping in the normal operating range, when the dynamic process of all control loops is considered. Without considering the dynamic reactive power support, the power angle of DFIG is limited to about 50°. Considering the dynamic process of all control loops, the limit of the power angle of DFIG is about 60°.

      • ZHOU Tao, LIU Zicheng, CHEN Zhong, WANG Yi, XU Yan

        Abstract:

        The new power system is gradually evolving into a low inertia power system with high penetration of DC and new energy, and the inertia of the load side is gradually increasing. Asynchronous motors occupy a high proportion in the load side, and their frequency support function needs further research. In order to evaluate the equivalent inertia of asynchronous motor under inertial time scale, a small signal model of asynchronous motor is established in electromechanical transient state. The transfer function of asynchronous motor power consumption and system frequency deviation is inferred in this paper. At the same time, the effective inertia of asynchronous motor to power system is inferred and the time-varying characteristics of asynchronous motor to power grid is analyzed. According to the idea of frequency support capability in inertia response stage, the factors which affect inertia frequency response of asynchronous motor are analyzed. The equivalent inertia evaluation model of asynchronous motor is proposed to quantify the frequency support capacity of dynamic load. Finally, a simulation model is built on Matlab/Simulink and PSASP platform to verify the correctness and effectiveness of the evaluation model and method proposed in this paper.

      • LIU Wenyuan, REN Bixing, LI Haifeng, WANG Haifeng, WANG Yang

        Abstract:

        With the continuous expansion of power grid scale, the phenomenon of subsynchronous oscillation caused by series compensated long-distance transmission system occurs frequently. Therefore, in order to analyze the deep reasons for the instability of the series compensated transmission system, based on the open-loop mode resonance theory, an open-loop mode resonance analysis method is proposed to analyze the subsynchronous oscillation caused by the series compensated transmission line. The small signal model of the external series compensated transmission line of permanent magnet synchronous generator (PMSG) farm is established, and the dynamic interaction between the series compensated line and the PMSG farm is studied through the open-loop mode resonance analysis method. The results show that the closed-loop stability of the system decreases when the open-loop subsynchronous oscillation mode dominated by series compensation is close to the open-loop subsynchronous oscillation mode dominated by wind farm in the complex plane. Using residual theory can successfully predict the position of closed-loop mode under the condition of open-loop mode resonance, while changing PMSG parameters or adjusting series compensation can avoid the occurrence of dynamic interaction. The correctness of the above theoretical analysis is verified by an example system in this paper. It is proved that there is a certain risk of instability when the PMSG farm transmits power through the series compensation transmission line, which can provide a reference for the parameter setting of the series compensation transmission system to a certain extent.

      • DONG Wenkai, REN Bixing, WANG Haifeng, WANG Yang

        Abstract:

        In recent years, sub-synchronous oscillation incidents have been reported to happen globally, which seriously threatens the safe and stable operation of the power system. As the capacity of a single wind turbine generator is small, a wind farm with tens even hundreds of wind turbine generators makes the order of the model of the wind farm high with the wind turbine generators complex coupled with each other. Reasonable and effective equivalent modeling of the wind farm is the basis for the study on the reasons, characteristics and suppression of the oscillations in the wind power integrated power system. In this paper, the advantages and disadvantages of the existing relatively thorough methods for wind farm equivalent modeling is analyzed based on the recognition of the reasons for the sub-synchronous oscillations in the wind power integrated power system. Then the issues in the field of equivalent modeling of the wind farm that need to be further studied are summarized, hoping to provide references for the future study of small-signal dynamic equivalence of a wind power collecting system and sub-synchronous oscillations of the wind power integrated power system.

      • Thesis and Summary
      • ZHOU Wei, SU Shiping, SU Jie, WANG Siyin

        Abstract:

        Considering the problems of distributed power output instability, parameter perturbation and load fluctuations in direct current (DC) microgrids, an improved auto-coupling proportional-integral (ACPI) bus voltage tracking control method with strong anti-interference ability based on a three-phase AC/DC converter is proposed. Firstly, the uncertainty of the internal dynamics and external disturbances of the DC microgrid is defined as a total disturbance, and thus the nonlinear uncertain system is mapped to an unknown linear system. Secondly, a controlled error system under the inverse excitation of the total disturbance is constructed. Based on that, an ACPI controller model based on the improved adaptive speed factor is designed, and it effectively suppresses bus voltage fluctuations and improves the dynamic response speed of the system. Finally, the robust stability and anti-disturbance robustness of the ACPI closed-loop control system are theoretically analyzed, and a simulation model is built for verification. The simulation results of DC bus voltage tracking under different working conditions show that the proposed control method has a fast response speed, strong anti-interference ability for improing stability on DC bus voltage fluctuations.

      • MEI Shufan, TAN Qinliang, DAI Mei

        Abstract:

        The problem of power abandonment and fluctuation with a high proportion of renewable energy connected to the grid can be solved by configuring energy storage. However, the cost of energy storage currently is high and it is difficult to promote and apply on a large scale. In addition, existing research focuses on planning for energy storage. The optimal capacity of energy storage in a single season ignores the impact of seasonal fluctuation in wind power and photovoltaic output on the scale of energy storage. In order to solve the above problems, an optimal allocation method for energy storage considering seasonal fluctuation of renewable energy output and load demand is proposed. The investment and operation cost of energy storage is calculated by the equivalent number of cycles. And the expected continuous discharge time is used to deal with the correlation of capacity and power. The capacity and power of energy storage are configured from the perspective of the full life cycle benefits of energy storage and the comprehensive utilization rate of wind and photovoltaic. The simulation results show that, compared with the pursuit of maximizing energy storage revenue or using a single typical day for energy storage configuration, the method proposed can not only ensure the economy of energy storage, but also further improve the utilization rate of renewable energy.

      • JIANG Yefeng, ZHOU Haiqiang, LUO Jianyu, SU Dawei, XIONG Hao, XIA Dongli

        Abstract:

        Due to lack of data or the complex statistical characteristics, it is difficult to ascertain the probability distribution of new energy and various loads when making dispatch decisions. A day-ahead optimal dispatch method of power system considering source and load interval uncertainties is proposed. Firstly, the interval number models of wind power, photovoltaic and various loads are established based on the prediction error. Secondly, taking the daily comprehensive operating cost as the objective function, and considering the constraints of generators, energy storage, and positive and negative backup, a mathematical model of interval optimal dispatch is constructed. Then, by applying interval optimization theory, the interval optimization problem is transformed into a deterministic problem under a certain interval possibility to solve, and the interval optimization dispatch scheme is obtained. Finally, the proposed method is applied in the modified IEEE 10-generator and 39-bus system to validate its effectiveness. The results show that the proposed method is flexible in decision-making. By adjusting the interval possibility degree, the economy and security of the dispatch scheme can be well balanced, and the amount of calculation is small. It is especially suitable for solving the optimal dispatch problem that only grasps the variation range of variables.

      • Power Grid Operation and Control
      • CHEN Guangyu, XU Jiajie, LU Zhaojun, YUAN Fei, ZHANG Yangfei, HAO Sipeng

        Abstract:

        Aiming at the practical problem of the difficulty in identifying associated users when abnormal line loss occurs in the station area, a method for judging and accurately locating the line loss abnormality in the station area based on the correlation measurement algorithm is proposed. Firstly, the optimal clustering number of the data set is determined by the gap statistics-contour coefficient fusion algorithm, and on this basis, the dichotomous K-means++ is used to construct the station area line loss standard library. Secondly, the station area line loss anomaly identification is completed based on the standard library and then the abnormal time is determined. The Spearman correlation coefficient (SCC) and Euclidean-discrete Fréchet distance (E-DFD) of each user's power and line loss during the abnormal time is calculated. And based on SCC and E-DFD, a comprehensive evaluation index to analyze user relevance is estabilished. Finally, the technique for order preference by similarity to an ideal solution (TOPSIS) is used to sort the comprehensive evaluation index values to achieve precise positioning of abnormally associated users. The calculation example uses real field data in a certain area to analyze, and the results show that the method proposed in this paper has better performance in clustering effectiveness, calculation time, and identification accuracy.

      • LI Zixuan, BAO Yuqing, SONG Meng, WANG Wei, CHENG Limin, CHEN Chen

        Abstract:

        As important demand-side resources, thermostatically controlled loads (TCLs) have great potential in suppressing fluctuations in renewable energy. However, traditional TCLs control strategy usually does not consider the control cost and the life loss caused by the high switching frequency of TCLs. In order to reduce the switch life loss of TCLs, a distributed cooperative control strategy for TCLs based on multi-agent consistency is proposed in this paper. Firstly, the concept of correcting switching time is introduced, and a control cost model that takes into account the thermodynamic characteristics of TCLs and switch life loss is established. Then, multi-agent consistency control is introduced, and the distributed cooperative control method is adopted to achieve the optimal control cost of TCLs. The results of calculation examples show that the proposed control strategy can reflect the thermodynamic characteristics of TCLs, thus greatly reducing the switch life loss under the premise of achieving the control goal.

      • WANG Ke, LU Yu, DONG Yunlong, MA Xiuda, LI Gang, WANG Jiacheng

        Abstract:

        In order to achieve the fault through of voltage source converter-based high voltage direct current (VSC-HVDC)system during alternating current (AC) system asymmetric faults and keep stability of the impedance at steadystate, a timely switch fault through method for VSC-HVDC system is proposed in this paper. Firstly, the positive and neg-ative sequence control of VSC-HVDC system and the effect of decomposition algorithm with 1/4 cycle delay on the impedance of VSC-HVDC system are analyzed. The high frequency impedance model on the AC side of VSC-HVDC system established. Then, on this basis, the AC fault is judged by the steady-state quantity and ab-rupt quantity of negative sequence voltage. In the steady state, the full sequence current control without positive and negative sequence decomposition is used to reduce the periodic fluctuation of the VSC-HVDC system impedance. In the transient state of fault, the negative sequence current control is superimposed to suppress the negative sequence fault current and realize the continuous operation of the system. Finally, model of VSC-HVDC system is developed in PSCAD/EMTDC to prove the validity of the proposed control method.

      • YU Haifeng, HUANG Jingjie, ZHU Sirui, JIANG Xing, YANG Hongming

        Abstract:

        The pre-listed balancing mechanism for monthly deviation is an effective method to deal with the power generation units imbalance electric energy in China's medium and long-term electricity transactions, but the traditional dispatching method is difficult to adapt to this mechanism. Therefore, under the pre-listed balancing mechanism for monthly deviation, a monthly rolling dispatching method for the imbalance electric energy in the power system including hydropower, thermal power and wind power is proposed. Firstly, a monthly electricity decomposition model considering the fairness of parties contract completion schedule is proposed. Secondly, based on the decomposed contract electricity, a day ahead scheduling model and a intraday scheduling model for power system including hydropower, thermal power and wind power are established. The objective function is to minimize the cost of emission reduction and balancing cost. Finally, the balancing cost of the monthly contract power deviation of generation units is minimized by rolling the daily deviation power in the month. Simulation results show that the proposed scheduling model and method can effectively reduce the monthly contract power deviation of generation units and the balancing cost, take into account the requirements of emission reduction.

      • Distribution Network and Micro-grid
      • GU Mo, DONG Shufeng, ZHANG Shupeng, WANG Hailin, JIAO Hao, CHEN Jinming

        Abstract:

        In the context of intelligent power consumption, household users can promote the safe, stable and economic operation of the power system by participating in electricity demand response and obtain additional benefits. Therefore, a strategy for demand response based on family agglomeration is proposed in this paper. Firstly, the concept of family clustering is proposed to manage the aggregation of residents' families into communities and to design the response mechanism on the residents' side. Secondly, considering the residents' electricity consumption habits and influencing factors during demand response, the responding load function of household electricity consumption is constructed, which quantifies the potential of household demand response. On this basis, a response strategy is designed which takes both the degree of completion and user experience into account. Finally, three specific indicators are proposed to evaluate the response strategy, namely task completion rate, user discomfort and economic benefits. An example is given to verify the effectiveness and economy of the proposed strategy.

      • ZHAN Hongxia, XIAO Junwen, DENG Xiaoyong, CHEN Tie, ZHANG Xi, HE Jiangtao

        Abstract:

        There are problems such as uncertain power output and load fluctuation when the distribution network with distributed generator (DG) operates on an island. In order to ensure stable and reliable power supply for islands, a dynamic island partition strategy is proposed which takes into account the standby demand of islands and gives full play to the flexible load regulation ability. Considering the uncertainty of wind power and photovoltaics, a prediction error model is established at first. The depth-first search algorithm is used to obtain the maximum power supply range for each time period, and chance constrained programming is used to deal with the random variables in the model, the island standby demands for each time period is obtained by the maximum power supply range. Then, modified particle swarm optimization (PSO) algorithm is used to give full play to the control ability of flexible load, and the optimal islanding results that meets the standby demand under each confidence levels is obtained with the objective of maximizing the comprehensive recovery value during the failure recovery period. Finally, a modified IEEE 33 node power distribution system is taken as an example to verify that the proposed strategy can effectively increase the value of islands while ensuring the reliability of islands.

      • ZHANG Jinhu, CHENG Yanxia, JIN Zhen, SUN Bolong, SONG Zhiwei, WEN Yu

        Abstract:

        There are many unmeasurable branches along with distribution lines. The sensitivity and speed of traditional three-stage overcurrent protection lacks when applied to these lines. Even the phasor differential protection cannot identify internal faults sensitively to maintain sufficient safety under external faults. With 5G communication is penetrating the field of power grid automation, a comprehensive protection scheme for branched distribution lines is proposed. Firstly, analyze negative sequence currents phase characteristics under internal or external faults, and negative-sequence current phase-comparison protection is proposed. Secondly, in some harsh working conditions, 5G communication's synchronization cannot be guaranteed, or even out of step. A positive sequence amplitude differential protection is introduced. Finally, the three-stage overcurrent protection is combined to form a complete set of protection coordination schemes when communication interruption or some extreme situations. A 10 kV active distribution network model is built in PSCAD/EMTDC to verify the proposed protection criteria and scheme. The simulation results demonstrate the effectiveness of the proposed protection criteria and scheme.

      • HOU Lan, LI Yujie, JIA Xiaoming, WANG Linjie, QIAN Cong, WANG Jian

        Abstract:

        With the rapid development of renewable energy (RE) and the continuous progress of smart grid, the energy consumption characteristic design of modern power system is developing towards a more flexible and economical microgrid (MG). Meanwhile, the high participation of multi-agent integrated energy in MG brings challenges to the efficient and economic operation of the system. Aiming at the complex capacity configuration of MG with multi-functional interaction, a combined capacity optimization method for a typical independent MG including photovoltaic (PV), wind turbines (WT), diesel generators (DG) and battery energy storage system (BESS) is proposed. On the one hand, the models of PV, WT, DG, BESS and electric vechicle (EV) charging load are established. On the other hand, the EV charging load are considered, and the capacity configuration is optimized to minimize the cost, reduce greenhouse gas emissions and energy waste. The results show that the combination of PV-WT-BESS-DG is not only more reliable but also more economical. This study can provide support for the optimal allocation of MG capacity.

      • High Voltage Engineering
      • YE Mingtian, PANG Lei, ZHANG Qiaogen, TAO Fengbo, XU Jiangang

        Abstract:

        To acquire the characteristic parameters which demonstrate the state of high voltage thyristor for clarifying its failure mechanism, an experiment platform which can not only generate high voltage pulses to thyristor at different moments during reverse recovery period, but also accurately measure its key characteristics is established. The change of characteristic parameters during the pulse impact process is studied, and the disassembly of the degraded and failed thyristors is analyzed. The results show that the damage of the thyristor can be mainly manifested as the reduction or loss of its blocking ability undertake voltage pulses in the middle of the reverse recovery period. Leakage current can be used as a characteristic parameter to estimate the state of the thyristor. For thyristors undertake voltage pulses in the beginning and middle of the reverse recovery period, obvious breakdown spot can be seen on the silicon wafer surface. Obvious breakdown points can be seen on the device chips that have been impacted and failed in the early and middle reverse recovery period. Circular spots formed by thermal stress can be seen on the device chips that are impacted in the middle of the reverse recovery period and have degraded blocking ability. Reverse recovery avalanche breakdown flash marks can be seen at the junction between the edge of the device chip and the insulating rubber that have been impacted and failed at the end of the period.

      • ZHAO Lihua, ZHOU Dongdong, WANG Zhong

        Abstract:

        The direct current (DC) transformation of alternating current (AC) lines is expected to alleviate the problem of excessive power supply pressure in some urban lines. It is necessary to study the current capacity and operation voltage to improve the power transmission capacity of the cable line after the transformation. The 10 kV three core AC cable in urban distribution network is used as an example to simulate the DC transformation under three laying conditions of air, direct buried and pipe laying. Firstly, the DC current capacity and suitable operation voltage range of the cable under three conditions are obtained according to the simulation results of temperature and electric field. Then, the maximum transmission power before and after the cable transformation is analyzed based on the current capacity and operation voltage of the simulation. Finally, the temperature field simulation of multi circuit line laying is carried out. The study results show that the power transmission capacity of DC cable which transforms from AC cable is improved, and the improvement of direct buried laying is the most obvious under three kinds of laying conditions.

      • ZHANG Xueqin, ZHOU Zhipeng, LI Qianhui, GUO Yujun, WU Guangning

        Abstract:

        Traditional indicators such as equivalent salt deposit density, surface pollution layer conductance and leakage current are mainly used to measure the contamination grades of ceramic insulators, and the detection process is time-consuming and inefficient. Hyperspectral technology can obtain rich information of target spectrum non-contact, and has great application potential in insulator pollution detection. Therefore, a method of ceramic insulator pollution level detection based on hyperspectral technology is proposed in this paper. Firstly, there is a reflection phenomenon when collecting hyperspectral image due to the material of ceramic insulator, so histogram equalization is used to process the hyperspectral image to remove the reflective interference. Then, the hyperspectral image is preprocessed to remove the noise interference. And the successive projections algorithm (SPA) is used to extract the feature of the sample spectral line for removing the redundant information. Finally, the classification model of support vector machine (SVM) is established according to the characteristic spectral lines, and the classification accuracy of ceramic samples is 95%.

      • DENG Honglei, YANG Hao, XIE Yue, LIU Gang, ZHAO Yifeng, FAN Xinghui

        Abstract:

        To study the changes in dielectric properties for thermally aged cross-linked polyethylene (XLPE) at different temperatures, the pure thermal and thermal-radiation aging tests are done. Thermal aging is carried at 80℃, 100℃, 135℃ and 155℃, lasting for 100 to 800 hours. The same conditions combined with 100 Gy/h gamma rays are done for thermal-radiation aged samples, and the dielectric spectra are measured from 25 to 200℃. The results show that the activation energy and values of β decrease obviously after the introduction of rays. At the same aging temperature and radiation conditions, electrical conductivity and relaxation peak frequency increase as the increasing aging time, which is a good reflection of dielectric properties during the aging process. Under different temperatures, the deviation in complex permittivity and modulus at lower frequency becomes more distinct compared with the values at a higher frequency. Finally, the dielectric properties under high temperature and low frequency could be a good indicator for the evaluation of XLPE degradation.

      • ZHANG Dongdong, LIU Xin, HUANG Xiaoning, ZHANG Zhijin

        Abstract:

        In recent years, the external insulation discharge and pollution flashover of transmission lines have occurred several times in the vicinity of nickel plant in Yancheng, and they cannot be effectively suppressed after the use of composite insulators. This phenomenon does not happened in the nearby chemical zone. Therefore, pollution samples of insulators are conducted in nickel plants and chemical plants within the jurisdiction of Yancheng power grid for analyzing and testing pollution chemical components, including anion and cation content, insoluble element composition, main compound composition. Then, based on the results of component analysis, a test under mixed pollution is carried out to obtain the flashover characteristics of composite insulators under typical pollution components of different pollution sources. Comparison between pollution composition of near chemical plants and nickel plants indicates that the latter has higher nitrates densities but lower chloride salts density. For one large and two small composite insulators, the flashover gradient under the typical pollution of nickel plants is 5% to 10% lower than that of chemical plants. For the external insulation configuration in heavy industrial dust areas, it is recommended to use one large and one small insulator to improve the electrical strength.

      • Smart Grid Technologies
      • LI Yang, YAN Qiang, FAN Youjie, SHI Yunpeng

        Abstract:

        Resident load is one of the important components of seasonal peak load and has huge demand response (DR) potential. But its randomness and decentralization limit the ability to flexibly participate in DR interactions. In view of the characteristics of resident load and the uncertainty of response behavior, the resident load model is established with the characteristics of load curve, historical DR participation and response degree as parameters. And the distribution parameters are identified through actual resident data sets. Furthermore, a method of forming a priority queue based on historical response effects is proposed. On this basis, the resident DR cost model is established, and the optimal resident DR strategy is obtained with the goal of cost minimization, so that the DR cost can be reasonably controlled under the premise of accurately achieving the load reduction target. The priority queue is updated and corrected successively in multiple DR events to realize automatic optimization of response strategies. Finally, the calculation example verifies the effectiveness of the proposed resident load model and the resident DR strategy self-optimization method.

      • ZHANG Min, XU Chunlei, ZHANG Qibing, PENG Zhiqiang, SHEN Jian, HOU Mingguo

        Abstract:

        In order to adapt to the trend of unattended substation, improve the debugging and maintenance efficiency of substation automation device, and at the same time meet the demand of flexible expansion of operation and maintenance business, the remote operation and maintenance technology of substation automation device based on micro-services architecture is studied. Firstly, the architecture and functions of the system are designed according to the operation and maintenance requirements. Secondly, the edge computing platform is developed, and the operation and maintenance business is realized by application (App) programs based on container technology. The plug and play process of device and Apps are designed, and active online interaction protocols are proposed. Finally, a operation and maintenance gateway based on micro-services technology is developed. The gateway has the characteristics of universal hardware, software decoupling and flexible functions. Apps such as virtual human-machine interaction, software version control, operation and maintenance debugging are developed. The system has been applied in a 220 kV substation in Nanjing, and the operation and maintenance efficiency is improved.

      • LI Qiang, ZHU Dandan, HUANG Di, WU Shengjun, YANG Yongbiao, SONG Jiaqi

        Abstract:

        Virtual power plant (VPP) is an important means of managing distributed energy. Reasonably formulating pricing strategies for VPP operators and electric vehicle (EV) users can guide EVs to fully consume renewable energy such as wind and solar, thus achieving a win-win situation for VPP operators and EV users. A stackelberg game model is firstly proposed in which a VPP with EVs is used as the electricity sales operator to participate in the orderly charging management of EVs. Operators formulate reasonable electricity selling prices through stackelberg game to guide the orderly charging of EVs, and coordinate various distributed resources to participate in the electricity market. Then, taking into account the volatility of wind power output and the uncertainty of conventional loads, the conditional value at risk (CVaR) theory is introduced into the modeling, and the model is transformed into a mixed integer linear programming problem solved by Karush-Kuhn-Tucker (KKT) conditions and dual theory. Finally, based on an example, the optimal pricing strategy and output plan of VPP operators are given. The influence of different EV proportions, maximum energy storage capacity, and risk preference coefficient on the optimal solution is analyzed, which provides optimization ideas for VPP operators to improve revenue.

      • Electrical Machines and Apparatus
      • CHEN Zhenfei, LI Chengying, MA Hongzhong, ZHAO Shuai, TANG Xiaozheng

        Abstract:

        With the development of UHV AC/DC transmission, synchronous condenser has been paid more and more attention because of its fast dynamic response ability. The safe operation of synchronous condenser is related to the stability of power grid. Taking TTS-300-2 dual water cooled synchronous condenser as the research object, and a three-dimensional model of its rotor is established. The three-dimensional temperature field of the rotor is calculated and analyzed under different loads and degrees of water blockage at the same position. The temperature field of the rotor with interturn short circuit fault and water blockage fault are calculated and analyzed. The thermal stress of the rotor with water blockage fault is also studied. Based on the analysis, the impacts of these faults and the ability of the synchronous condenser to operate are evaluated. The results show that the distribution of rotor temperature field is similar under different loads. Rotor fault leads to unbalanced temperature distribution. The more turns of blockage in a single slot, the more obvious temperature distortion of the rotor. The thermal stress of rotor increases with blockage degree.

      • WANG Lihui, ZHANG Wenpeng, AN Yiyan

        Abstract:

        Focusing on the problem that it is difficult to distinguish the nonlinear errors such as drift error and ratio error of fiber optic current transformer (FOCT), an error recognition method based on complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN)and zero-crossing rate (ZCR) is proposed. Firstly, the output signal of the FOCT is decomposed using CEEMDAN algorithm to obtain the intrinsic mode functions (IMF) containing nonlinear error characteristics, which constitutes the original error vector data set. Then, the number of components under different errors is compared. The ZCR index of each IMF component under different errors is calculated by ZCR algorithm. The results are used to classify the IMF. Finally, the IMF component signals are divided into three categories according to the ZCR index. IMF components are superimposed and reorganized into three components, and IMF component signals with stable number of decomposition results are constructed. Error identification is realized according to the expression forms of different components. Experiment results show that the CEEMDAN-ZCR based error recognition method can effectively identify the two kinds of errors. The drift error characteristics are mainly concentrated in the third layer of IMF (C3), and the variation ratio error is mainly concentrated in the second layer of IMF (C2).

      • ZHAO Wenqiang, SHI Qiaoming, WANG Yongping, LU Yu, WANG Bingqian, CHANG Haotian

        Abstract:

        Aiming at the fault overcurrent problem existing in the current arrangement scheme of the bridge arm reactor in the modular multilevel converter (MMC) of the bipolar flexible DC transmission system, the influence of the bridge arm reactor in different positions on the converter fault current is analyzed in this paper, and the mathematical expression of fault current component is derived. A scheme of placing the bridge arm reactor near the DC connection point is proposed. The study shows that the arrangement of bridge arm reactor near the DC connection point can effectively limit the rise rate of fault current, reducing the overcurrent level of the bridge arm module without increasing larger costs. However, when the bridge arm reactor is arranged close to the DC connection point, the short circuit fault of the bridge arm reactor wall bushing cannot be detected in time by the existing protection strategy, which brings potential threats to the MMC. A protection strategy, which can effectively identify the short circuit fault of the bridge arm reactor wall bushing is proposed in this paper. Finally, the correlation analysis and protection strategy are verified by PSCAD/EMTDC simulation.

      • Technology Discussion
      • HAN Xiaojuan, MU Zhiguo, WEI Zixuan

        Abstract:

        The energy storage system is a complex energy system that changes with time. Multiple indicators are required to describe its performance, and different application scenarios have different requirements for the energy storage system. To solve the above problems, a cloud model-based method for evaluating the adaptability of electrochemical energy storage conditions is proposed. In the application scenario of energy storage participating in power grid peak and frequency regulation, comprehensive evaluation indicator domain and standard domain for energy storage system suitable for power grid peak regulation and frequency regulation are established firstly. Then, the entropy weight method is used to calculate weight matrix of energy storage system evaluation indicators. The forward cloud generator is used to calculate the membership matrix of the decision-making indicators of the energy storage system to be evaluated. Finally, the comprehensive score of the adaptability of the energy storage system to be evaluated is calculated according to the fuzzy subset on the comprehensive evaluation standard domain of the energy storage system, and the one with the highest score is selected as the best energy storage system for this application scenario. The working condition adaptability of five electrochemical energy storage systems is simulated and analyzed. The results show that the lithium iron phosphate battery has the highest score. The lithium iron phosphate battery has the best working condition adaptability in the peak and frequency regulation scenario, which is consistent with the actual engineering.

      • WANG Yuanyuan, BAI Hongkun, WANG Shiqian, BU Feiei, WU Xiong, LI Haoyu

        Abstract:

        With the development of new technologies in power system and the implementation of flexible policies such as demand response, traditional power consumers are gradually turning into prosumers, and their power consumption habits are also evolving and changing. In this paper, the features of power users and the potential value of massive power consumption data can be described and fully utilized by portrait technology. A method of power users' behavior portrait based on information gain and Spearman correlation coefficient is proposed. Firstly, k-means clustering algorithm based on gap statistic is used to analyze the power users' consumption data. Then, considering the effectiveness and redundancy of the feature set, the adaptability evaluation coefficient is introduced. On this basis, the optimal feature subset is obtained by genetic algorithm. Furthermore, quantitative analysis is implemented to characterize the portrait of power users. Several case studies are presented to demonstrate the effectiveness of the proposed method.

      • WANG Yunlong, SHAO Junren, CHEN Kaizhi, MO Juyue, ZHANG Qunqun, CAO Pulin

        Abstract:

        The ice-shedding may induce isolated ground wires temporary grounding during de-icing, which can cause the protective relay of direct current de-icing devices triggered frequently and unnecessarily. After analyzing the circuit of the grounding isolated ground wire, the conclusion can be obtained that the temporary grounding of isolated ground wires leads to the fluctuation of electric quantities. On the basis of above analysis, the permutation entropy is applied to describe the trend of the voltage waveform, which is able to overcome the influence of high frequency harmonics caused by converters. Based on the voltage trend acquired by the permutation entropy, the variance is employed to determine the fault and the disturbance. Then, parameters of the de-icing device in Kunbei substation is utilized for simulation. The simulation results verify the effectiveness of the proposed method, which can be performed to identify the disturbance induced by de-icing and the permanent fault.