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  • 1  Optimal planning of charging stations for electric vehicles based on voltage stability of distribution system
    CHENG Shan XU Linfeng SUN Weibin SU Gaocan FENG Yuzhang
    2020, 35(4):3-12. DOI: 10.19781/j.issn.16739140.2020.04.001
    [Abstract](929) [HTML](0) [PDF 1.09 M](4659)
    Abstract:
    The disordered planning and unreasonable allocation of electric vehicle charging stations have a serious impact on the safty,stability and economy of the distribution network operation.To solve this problem, this paper constructs an optimal planning model of electric vehicle charging stations based on the voltage stability index of distribution network.The model not only could balance the construction investment of charging stations,the economic operation of distribution system and the quality of power supply,but also take full account of the demand and convenience of the electric vehicle charging.The improved adaptive particle swarm optimization (APSO) algorithm with fast speed and high accuracy is adopted to solve the nolinear optimization problem with multiple constraints. Finally, the simulation results based on IEEE33bus system show the effectiveness of the proposed method.
    2  Comparative study of typical analysis methods for the LLC resonant converter
    YAN Xiangwu LIU Xinxin SUN Lei LV Zheng
    2020, 35(4):128-132. DOI: 10.19781/j.issn.16739140.2020.04.017
    [Abstract](886) [HTML](0) [PDF 1.08 M](2868)
    Abstract:
    The LLC resonant converter can achieve softswitching while it operates in highfrequency and then improves the power density and efficiency of power supply. The fundamental approximation and mode analysis are two classic analysis methods of LLC resonant converter, but the comparative studies in the voltage gain accuracy, efficiency and application is not intensively discussed. On this background, the principle of the above methods is illustrated firstly. Then, the operation mode of LLC resonant converter is analyzed in PSIM simulation environment. Based on the operation modes, the voltage gain accuracy of the two methods is compared in simulation. Finally, the resonant parameters are selected based on the peak voltage gain, and a 1.5 kW/28 V prototype is set up. The experimental results show that actual gain is higher than the gain curve based on FHA 10% to 15% below the resonant zone, and have high accordance with the voltage gain based on the mode analysis in whole frequency range. And the iterative parameters based on mode analysis have higher efficiency with the experimental prototype.
    3  An assessment mechanism for contract energy deviation in a mediumand longterm electricity market
    CHEN Zhongyuan LIN Zhemin HE Chuan QIAN Hanhan ZHANG Zhi LIN Zhenzhi WEN Fushuan
    2020, 35(1):31-39. DOI: 10.19781/j.issn.16739140.2020.01.004
    [Abstract](676) [HTML](0) [PDF 955.91 K](732)
    Abstract:
    Before the spot electricity market is established, electrical energy is traded through forward contracts in the current medium and longterm electricity market in China. A reasonable balancing and settlement mechanism for electrical energy deviation is conducive to the smooth transition from the mediumand longterm electricity market to the spot market. Given this background, an assessment mechanism is presented for contract energy deviation in a mediumand longterm electricity market. First, the deviation settlement mechanism of the basic rules for the mediumand longterm electricity market is examined, and a generationside deviation balancing mechanism suitable for the current electricity market environment proposed. Then, considering the differences of the marketoriented electricity proportion and the differences in the capabilities of various users in controlling contract deviations, the risk of the electrical energy deviation penalty imposed on demand customers is analyzed. A fixedratio energy deviation settlement method is next designed for nontotal electrical energy transaction, and a staged assessment mechanism of demandside energy deviation proposed. Simulations based on actual deviation assessment data from a provincial electricity market in China show that the proposed energy deviation assessment mechanism is effective in the mediumand longterm electricity market.
    4  Analysis of the effect of phaselocked loop on input admittance of converter station in flexible DC transmission system
    LI Peifa TANG Xin WANG Wen LI Tian
    2020, 35(4):20-26. DOI: 10.19781/j.issn.16739140.2020.04.003
    [Abstract](534) [HTML](0) [PDF 1.10 M](2669)
    Abstract:
    The accuracy of the impedance model of the converter station directly affects the small interference stability analysis of the flexible DC transmission system. However, the more accurate the model, the higher the order, which increases the complexity of the analysis. To analyze the influence of the phaselocked loop on the impedance characteristics of the converter station, we firstly establish the admittance matrix of the AC side of the converter station under the two conditions of dq coordinates with and without consideration of the phaselocked loop, and then establish the same order and mirror admittance of the converter station at the static coordinates. By comparing and not considering the input admittance of the phaselocked loop, it is concluded that the influence of the phaselocked loop on the input admittance value is directly related to the cutoff frequency of the phaselocked loop transfer function. Finally, the simulation model is established in PSCAD software. We use the signal injection method to obtain the homologous and mirror admittance of the converter station to verify the correctness of the theoretical analysis.
    5  Analysis of "2·15" blackout in Texas and its enlightenment to China's new power system supply adequacy
    Li Zhengqi Cai Ye Cao Yijia Li Long Tan Yudong
    2022, 37(5):17-24. DOI: 10.19781/j.issn.1673-9140.2022.05.002
    [Abstract](509) [HTML](0) [PDF 1.34 M](409)
    Abstract:
    With the fast development of the economy and society, the reliable supply of electricity has triggered a wide range of concerns. On 15th, February, 2021, a large-scale power outage occurred in Texas, USA due to the extremely cold weather. More than 4.8 million users are affected. This accident has a serious impact on industrial production and people's lives. Firstly, the general situation of the power system in Texas is briefly introduced, and then the specific process of the blackout is described in chronological order. After that, the causes of the blackout event are analyzed from three aspects: grid adequacy, regional support capability, and the market mechanism. Finally, from the perspective of the construction of China's new power system, some inspirations are proposed for the meteorological forecasting technology applications, the power supply structure of the new power system, the flexible resource and integrated operation of the source-grid-load-storage system, and the construction of the grid structure of the power grid. This work provides a reference to help guarantee the adequacy of the power supply in China's new power system.
    6  Transmission line aerial image recognition of insulator strings based on color model and texture features
    TANG Bo QIN Qiao HUANG Li
    2020, 35(4):13-19. DOI: 10.19781/j.issn.16739140.2020.04.002
    [Abstract](503) [HTML](0) [PDF 1.01 M](2121)
    Abstract:
    With the construction of smart grid, power companies gradually use unmanned aerial vehicles (UAV) to replace manual inspection of transmission lines. This paper proposes a method for processing aerial images of transmission line insulators captured by UAV. Firstly, the threshold and range of RGB components in the color model are used to segment the target and background areas. Secondly, mathematical morphology and nonoverlapping window texture features are applied to roughly mark the target area. Finally, a minimum circumscribed horizontal rectangular frame is generated. Then the texture features of all the patterns within the minimum circumscribed horizontal rectangular frame are identified to locate the minimum horizontal rectangular area of the aerial image of the insulator string. In the end, we use two images to verify the algorithm and compare with the algorithms in the literature. The results show that the algorithm proposed in this paper can better identify the position of insulator strings.
    7  Decomposition of an electrical energy contract for difference in electricity market environment
    LI Daoqiang GONG Jianrong LI Zhonghui GAO Ying WEN Fushuan
    2020, 35(1):40-49. DOI: 10.19781/j.issn.16739140.2020.01.005
    [Abstract](501) [HTML](0) [PDF 962.22 K](572)
    Abstract:
    The wellestablished contract for difference (CfD) is a middleor longterm financial contract. When the CfD is applied in the electricity market, the electricity price can be fixed and the risk associated with the fluctuated electricity price in the spot market avoided. In recent years, with the advance of the power industry restructuring and the expansion of the pilot scope in China, the electrical energy CfD is included in the designed electricity market mechanisms in several provinces. Currently the implemented CfD contracts for electricity in provincial electricity markets in China are actually electrical energy contracts rather than electrical power ones, and hence it is necessary to decompose the contracted electricity energy into dispatchable electrical power demand curves. A brief overview of the electrical CfD is first presented, and the existing theories and methods from the perspectives of the rolling correction and optimization models based decomposition algorithms for definite contracted electrical energy are presented and compared. Finally, some problems associated with the decomposition of the contracted electrical energy in this round of power industry restructuring are prospected, and possible solved methods addressed.
    8  Research on three optimized grounding schemes of HV cable cross connection system
    WU Zhixiang ZHOU Kai HE Min
    2020, 35(3):135-140. DOI: 10.19781/j.issn.16739140.2020.03.018
    [Abstract](494) [HTML](0) [PDF 0.00 Byte](0)
    Abstract:
    In order to reduce the induced voltage at the metal sheath of cables, as well as the circulation current of sheath in the cross interconnected grounding mode, the grounding mode of sheath is modified for the reconstruction of cable lines. Based on the defects of cross interconnection grounding in t he practical application, three kinds of the optimization scheme for grounding protection are proposed. There are the grounding of one side of the protective layer through the compensating inductance, single terminal grounding through the cross connection, and grounding at each section. The simulation models are built by utilizing PSCAD simulation software to study the voltage and circulation current at sheaths under different schemes. Theoretical analysis and simulation results show that those three kinds of cable sheath grounding can effectively suppress the metal sheath end induction high voltage. The sheath circulation current produced after the line reconstruction can be reduced. The optimization schemes for cable sheath grounding can be utilized as the engineering practice in the future direction of promotion.
    9  Detective effect of oscillation on different defects of cable from the perspective of materials and electric field
    YUAN Jihe YANG Yang ZHANG Xi HUANG Huayong WANG Xianjin ZHOU Kai
    2020, 35(4):42-48. DOI: 10.19781/j.issn.16739140.2020.04.006
    [Abstract](491) [HTML](0) [PDF 1.43 M](2161)
    Abstract:
    The effect of the oscillating wave on the interfacial and internal defects of cable from the perspective of the electric field is studied in order to understand the test results of the oscillating wave voltage method for different defects in cables. Firstly, an oscillating wave test platform is set up to partial discharge tests the artificial defective models including longitudinal knife defects and external semiconductor lap defects. Then, the excitation characteristics of oscillation wave are analyzed primarily by PDIV and PRPD. Furthermore, the electric field distribution of cables with defects are simulated by utilizing a finite element simulation software in threedimension. Artificial defects with different sizes are fabricated to represent the diversity of the defect site and the characteristics of defective discharges are explained by the electric field distortion at the defects. Experimental and simulation results show that: it is hard to detect the internal defects due to the filling of hard grease by using the oscillation wave voltage method, whereas interfacial defects of poor connection of outer semiconductor has better characterization results.
    10  Study on calculation methods for DC component and decay time constant of branch short circuit current
    Cao Wei Zhang Zheng Chen Chunyang Zhang Jie
    2021, 36(2):31-39. DOI: 10.19781/j.issn.1673-9140.2021.02.004
    [Abstract](446) [HTML](0) [PDF 1.03 M](1143)
    Abstract:
    As the voltage level of the power system increases, the DC component influence on the breaking capacity of the circuit breaker has been closely concerned. However, there are few studies on the calculation method of DC component of short circuit current in the circuit breaker branch. In this paper, a calculation method is proposed for the DC component of branch short-circuit current and its decay time constant based on transfer impedance. Firstly, in the case of knowing the impedance matrix of the original network and considering the characteristics of the network when the system is short-circuited, the network is transformed based on the principle of forming the node impedance matrix using the branch-adding method.Then, the transformed network can easily calculate the DC component of the short-circuit current and the decay time constant of each branch. In addition, a unified algorithm for forming the node impedance matrix is concluded when considering the changes of the network topology. It has the advantages of fast calculation speed, clear physical concept, and it is easy to program so as to achieve scanning calculations. The accuracy of the proposed method is verified by EMTP simulation. Compared with results from PSS/E, the superiority of the proposed method is also verified.
    11  Method of fault section location for the small current singlephasetoground fault based on the amplitude analysis of threephase current
    WAN Xinshu FANG Lianhang LIANG Yu WU Qiang LIU Hongyan
    2020, 35(4):49-57. DOI: 10.19781/j.issn.16739140.2020.04.007
    [Abstract](429) [HTML](0) [PDF 1.60 M](2065)
    Abstract:
    Singlephasetoground fault section location in small current grounded system is generally realized by a master station comprehensively calculating several different electrical quantities. This method is unsuitable for distribution networks with complex structures since its large workload and complicated calculations easily brings large errors. Under the background, a fault location method of distribution network based on threephase current amplitude analysis is proposed. In views of the analysis on the threephase current of singlephasetoground fault in small current grounded system, the current changes of the two nonfault phases on the fault path are approximately equal and less than the current change of fault phase. The phase current change of the two nonfault phases on the nonfault path are approximately equal and also equal to the current change of fault phase. By calculating the amplitude change of threephase current before and after fault and setting the criterion, the fault phase can be selected and the fault section can be located. ATP simulation results verify the applicability in neutral ungrounded system and neutral point grounding system via arc suppression coil. The local location of fault is realized successfully. The proposed method is simple in location criterion and reduces the computational complexity of the master station.
    12  Overview of transient overvoltage mechanism and suppression strategies of high voltage direct current transmission grid
    LIN Sheng LAN Feiyan LIU Jian LI Xiaopeng
    2022, 37(6):3-16. DOI: 10.19781/j.issn.1673-9140.2022.06.001
    [Abstract](416) [HTML](0) [PDF 1.54 M](605)
    Abstract:
    Commutation failure, DC blocking and near AC short-circuit fault of HVDC transmission system would lead to transient overvoltage of sending-end power grid, restrict transmission capacity and threaten safe and stable operation of system. For this reason, this paper firstly gives the similarities and differences of the transient overvoltage generation mechanism of DC sending-end power grid under three typical fault conditions of commutation failure, DC blocking and near-field AC fault are analyzed systematically, and the main influencing factors of transient overvoltage are clarified. Secondly, the existing transient overvoltage suppression strategies and their advantages and disadvantages are summarized. Finally, in view of the shortcomings of the existing research, it is analyzed that the three aspects of analyzing the transient overvoltage mechanism of different new energy transmission scenarios, revealing the coupling law of multiple influencing factors of transient overvoltage, and constructing a multi-temporal and spatial scale transient overvoltage collaborative suppression system are the focus of future research on transient overvoltage of HVDC sending-end power grid.
    13  Location and selfhealing of singlephase grounding fault based on distribution automation
    YANG Fu ZANG Xuan QU Hanbing LIN Shan GU Shilong CHEN Hao
    2020, 35(4):176-181. DOI: 10.19781/j.issn.16739140.2020.04.024
    [Abstract](414) [HTML](0) [PDF 908.04 K](2185)
    Abstract:
    Aiming at the nondirectly grounded distribution network of neutral point, this paper proposes to connect the small current fault line selection device to the distribution automation system. When a singlephase ground fault occurs, through the onoff control of the intelligent switch on the line and sequential logic of singlephase grounding alarm signal to determine the fault interval.Then the method isolates the fault area through the distribution automation system, restores the power supply in the nonfault area, and realizes the singlephase ground fault selfhealing of the distribution grid. In the end, this paper verifies the effectiveness and necessity of this strategy by experiments.
    14  Prediction of transformer oilpaper insulation aging based on BP neural networks with the chicken swarm optimization algorithm
    YUAN Jiabo XU Pengcheng LI Lei LIU Yanwen WANG Xin ZHENG Yihui
    2020, 35(4):33-41. DOI: 10.19781/j.issn.16739140.2020.04.005
    [Abstract](411) [HTML](0) [PDF 1.03 M](2138)
    Abstract:
    In order to study the relationship between the aging and the polarization/depolarization current (PDC) of transformer oilpaper, a prediction method of transformer oilpaper aging is presented based on the BP neural network with the chicken swarm optimization algorithm. Firstly, the relationship between extended Debye parameters and the polymerization degree (DP) of oilpaper is examined. With the variation of atmosphere temperature, PDC changes and it leads to a failure of extended Debye model to response the aging status of oilpaper. In order to eliminate the error caused by temperature, a BP neural network is trained through fitting PDC and DP of oilpaper. Then, in view of the slow convergence and low efficiency of BP neural network, the chickens swarm algorithm is utilized to optimize weights and threshold of the BP neural network. After the optimization, the network convergence is speeded up and the possibility of trapping into local optimal is also reduced. Finally, the simulation results show that the environment influences to polarization/depolarization current are reduced and the oilpaper polymerization degree is predicted accurately.
    15  Optimally selected objective and model predictive control based optimal strategy of wind power with energy storage
    YAN Xiao CHENG Shan ZUO Xianwang WEI Kanglin
    2023, 38(1):1-10. DOI: 10.19781/j.issn.1673?9140.2023.01.001
    [Abstract](403) [HTML](0) [PDF 1.56 M](569)
    Abstract:
    Aiming at the problem that the wind storage system's power fluctuation suppression effect is unsatisfactory, the wind storage system's operation is optimized. Considering the time series coupling characteristics of wind storage system operation and the influence of future wind power fluctuation on the energy storage system (ESS), an optimization strategy based on stabilizing target optimization method and model predictive control (MPC) is proposed. Firstly, the expected grid?connected power is calculated according to the predicted wind power and the constraints of ESS, and the local prediction accuracy is introduced to correct it. Then, combined with the current state of charge (SOC) of ESS, the optimal stabilization target is obtained by fuzzy control; Lastly, the MPC with particle swarm optimization (MPC?PSO) strategy is used to optimize the ESS power, so as to minimize the difference between the grid?connected power of next time and the optimal target power and minimize the ESS power. The simulation results show that the strategy proposed in this paper has a better wind power fluctuation smoothing effect and can effectively reduce the operation cost of energy storage.
    16  Research on threephase load imbalance treatment based on the seamless commutation device
    CAO Lei HU Pengfei WANG Rui
    2020, 35(4):99-106. DOI: 10.19781/j.issn.16739140.2020.04.013
    [Abstract](389) [HTML](0) [PDF 1.10 M](1047)
    Abstract:
    The threephase load imbalance seriously influences the safety, economic and reliable operation of distribution network. On this background, a control strategy of the SCR is proposed in this paper. Firstly, on the basis of the seamless commutation device, a mathematic model of threephase load imbalance treatment system in distribution network is established. Then, the vectorgenetic algorithm is utiliazed to realize the threephase load imbalance treatment and the optimal phase allocation scheme of the distribution area is obtained. Finally, the feasibility of the algorithm is verified by the simulation. The seamless commutation devices are installed in the low voltage distribution area and the experimental results validate the correctness and feasibility of the proposed control scheme.
    17  APWM control strategy of fixed frequency LLC resonant converter for wide voltage applications
    Pan Jian Liu Songlin Shi Di Song Haojie Xiong Jiaxin
    2022, 37(5):80-87. DOI: 10.19781/j.issn.1673-9140.2022.05.009
    [Abstract](381) [HTML](0) [PDF 1.95 M](449)
    Abstract:
    The conventional frequency-controlled LLC resonant converter suffers from wide frequency regulation range and low conversion efficiency, so that it is unsuitable for wide voltage range applications with a wide voltage range. In order to solve these problems, a PWM control strategy of the full-bridge LLC resonant converter is proposed in this paper, which realizes the gain adjustment by adjusting the duty cycle of the switch The switches of two lower arms of the resonant converter are controlled by a fixed frequency, and the switching frequency is equal to the resonant frequency, while the switches of the two upper arms are controlled by PWM to adjust the output voltage. With the method, the frequency variation range of the resonant converter is significantly narrowed. In addition, the switches of primary circuit and the rectifier diodes of secondary circuit could achieve zero voltage switching (ZVS) and zero current switching (ZCS), respectively, which effectively reduces the switching losses of the converter. Finally, the 1.5 kW simulation and experimental prototype with 400 V input voltage, 250~500 V output voltage are established to verify the effectiveness of the proposed PWM control strategy.
    18  Research and application of modeling method of secondary cable loop in intelligent substation
    HAO Xiaoguang GENG Shaobo REN Jangbo YANG Jingchao ZHOU Kun ZHANG Bingwang
    2020, 35(4):161-168. DOI: 10.19781/j.issn.16739140.2020.04.022
    [Abstract](379) [HTML](0) [PDF 1.48 M](3132)
    Abstract:
    Due to the lack of secondary cable circuit model, the information model of intelligent substation is incomplete. It is not only harm to intelligent substation comprehensive online monitoring and operational diagnosis, but also infect the development of smart substation Informationization. In this paper, a modeling method for secondary cable loops in the intelligent substation is proposed firstly. Then, the secondary cable loop configuration process is designed and the secondary cable loop model structure is introduced. The multidimensional visual display of secondary subcircuit for the intelligent substation is realized by the secondary cable loop model file visualization tool. Finally, the secondary cable loop information model is associated with the physical model by mapping the information model in the SCD file to the secondary cable loop model. The online monitoring and fault location of the secondary cable loop of the intelligent substation is realized successfully.
    19  A new method of fast simulation for electromagnetic transients of SVC and TCSC
    XU Shengyang MAO Xiaoming MAI Liyun
    2020, 35(4):66-75. DOI: 10.19781/j.issn.16739140.2020.04.009
    [Abstract](374) [HTML](0) [PDF 1.60 M](2031)
    Abstract:
    In the traditional electromagnetic transient simulation, the computation speed of SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series Compensation) is relatively slower. In order to overcome this deficiency, a new method of fast simulation for the electromagnetic transients of SVC and TCSC is proposed. For the fact that the state equations of SVC and TCSC are unchanged when the state of TCR (Thyristor Controlled Reactor) branches stay the same, the piecewise timeinvariant state equations of SVC and TCSC are developed firstly. Then, auxiliary variables are introduced and the model is transformed from a set of nonhomogeneous linear equations into homogeneous ones to obtain the unified expression suitable for varied working conditions. Finally, the scaling and squaring method is utilized to compute the matrix exponent and the response of the model is obtained. The feasibility and high efficiency of the proposed method is verified by comparing with the results from classical electromagnetic transient simulations using the PSCAD/EMTDC software package.
    20  Joint optimization of windthermal bundling transmission line crosssection and thermal power capacity considering heat capacity
    ZHANG Mengjie YE Rong LIN Zhangsui WEN Buying
    2020, 35(4):91-98. DOI: 10.19781/j.issn.16739140.2020.04.012
    [Abstract](373) [HTML](0) [PDF 988.92 K](4327)
    Abstract:
    Windthermal bundling external power transmission use thermal power to suppress the fluctuation of wind power and improve the utilization rate of the line. It is an important way to absorb wind power on a large scale. Therefore, the choice of windthermal bundling external power transmission lines and supporting thermal power is crucial. And the transmission capacity of the external power transmission line is related to its cross section and environmental temperature. Considering the line heat capacity or namely the influence of environmental temperature, this paper proposes a method to optimize transmission line crosssection and thermal power capacity of windthermal bundling external power. This method comprehensively considers the impact of wind power and thermal power income, total cost of thermal power, line investment cost, and wind curtailment cost on social benefits. The calculation example shows that this method can give full play to the transmission capacity of the line and increase social benefits compared with the method without considering the thermal load capacity.

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