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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](930) [HTML](0) [PDF 1.09 M](4663)
    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  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.
    3  Analysis of charging power demand of electric vehicles considering the influence of travel temperature
    Zhang Xincheng Liu Zhizhen Hou Yanjin Zong Shasha
    2021, 36(4):124-131. DOI: 10.19781/j.issn.1673-9140.2021.04.016
    [Abstract](198) [HTML](0) [PDF 1.40 M](3610)
    Abstract:
    Travel temperature directly affects the specific energy consumption of electric vehicle through various interferences, resulting in the difference in charging power demand at different temperatures. According to the statistical principle, under the support of a large number of samples, the least squares method to obtain the specific relationship between the electric power consumption per km of electric vehicles and the travel temperatures in this paper. Then a power calculation model for electric vehicles considering the influence of travel temperature is proposed. The distribution network of a certain residential district in Beijing is taken as an example. Monte Carlo method is used to simulate the specific difference of electric vehicle charging load under different seasons (temperatures). The different impacts of EV load on the regional power grid in different seasons are analyzed to provide a new seasonal scheduling idea for the orderly control of EV charging behavior in the future.
    4  A novel dynamic detection approach for power system operation section based on Qlearning algorithm
    Li Bao Wu Yunliang Deng Weisi Li Peng
    2021, 36(4):116-123. DOI: 10.19781/j.issn.1673-9140.2021.04.015
    [Abstract](269) [HTML](0) [PDF 1.06 M](3548)
    Abstract:
    Power grid operation section is an important measure in power system operation control. Faced with the numerous intelligent generation methods of grid operation sections at present, how to make a reasonable choice has become an important content of the research in the field of online generation algorithms for grid operation sections. To solve this problem, a dynamic detection method for power grid operation section based on Qlearning algorithm is proposed. The main feature of this method is that the Qlearning agent is trained, and the grid operation section generation method is dynamically selected according to the grid operation characteristics, so as to make full use of the algorithm advantages of different generation methods in different scenarios. Finally, a case study based on the actual data in a certain provincial power grid shows that the dynamic detection method can improve the accuracy of the generated results by optimizing the selection of the detection algorithms in different scenarios. For the applied sample set, the method could improve the accuracy by nearly 5.2%.
    5  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](381) [HTML](0) [PDF 1.48 M](3133)
    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.
    6  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](889) [HTML](0) [PDF 1.08 M](2886)
    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.
    7  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](535) [HTML](0) [PDF 1.10 M](2671)
    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.
    8  Research on parameters setting of Siemens PSS3B power system stabilizer
    LI Li HONG Quan GUO Siyuan CAI Yuhua WU Jinbo
    2020, 35(6):157-162. DOI: 10.19781/j.issn.16739140.2020.06.021
    [Abstract](169) [HTML](0) [PDF 619.89 K](2545)
    Abstract:
    The parameters of Siemens PSS3B power system stabilizer are difficult to tune, therefore, a parameter tuning method is proposed in this paper. Firstly, the PSS3B feedback transfer function structure is equivalently converted into a series transfer function structure by analyzing the transfer function structure of the power system stabilizer. Then the phase compensation parameters of transfer function is adjusted based on the phase compensation principle. Finally, the gain coefficient of the power system stabilizer is adjusted by checking the damping ratio corresponding to the dominant characteristic root of the closedloop transfer function and the oscillation frequency. After the adjustment, the PSS3B power system stabilizer has a good suppression effect on the lowfrequency oscillation of active power, which verifies the effectiveness of the method.
    9  Study on the energy management system of an electric vehicle and renewable energy in home microgrid
    HAN Feng ZENG Chengbi MIAO Hong
    2021, 36(1):79-86. DOI: 10.19781/j.issn.16739140.2021.01.009
    [Abstract](202) [HTML](0) [PDF 1.00 M](2334)
    Abstract:
    The home microgrid contains uncertain power sources and loads such as photovoltaics and electric vehicles. The lack of a reasonable energy management strategy can easily lead to instability of the household microgrid.In the V2G system, a model that simultaneously considers electric vehicles, houses, batteries, and renewable energy power generation systems is constructed. Under the restriction of electric vehicle charging and discharging strategy, a power production planning for the residence and for the microturbine is determined.Then a dynamic energy management is proposed. Finally, the proposed home microgrid energy management method is verified by simulation. By comparing the equivalent load and energy storage operation of the microgrid under the conditions of random charging, orderly charging and discharging of electric vehicles,the feasibility of proposed method is verified when the charging state of the battery is restricted.
    10  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](2190)
    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.
    11  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](2171)
    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.
    12  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](2144)
    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.
    13  Nonamplitude difference control of microgrid based on DCside current control of inverter
    XIE Dong YANG Huanhong DING Yutao WANG Jie
    2020, 35(4):107-113. DOI: 10.19781/j.issn.16739140.2020.04.014
    [Abstract](365) [HTML](0) [PDF 1.05 M](2141)
    Abstract:
    In the microgrid with the energy storage system as the main power source, the output characteristics of the energy storage system directly affect the power quality of the microgrid. When the output of the energy storage system can not be adjusted quickly, the problem occurs that the power quality of the microgrid does not meet the requirements. The traditional V/f control strategy adopts the reactivevoltage droop control strategy. When the island is running, there is a voltage offset, which will affect the overall power quality of the microgrid. And in the droop control, the droop coefficient parameter selection inevitably leads to misadjustment. In order to solve these problems, this paper discusses the relationship between the DC and AC power of the inverter. Based on the implementation of the control strategy of the energy storage inverter, DC current control is added to solve the problem of voltage offset and misadjustment to achieve nonamplitude difference control of microgrid. Finally, the PSCAD software is used to build the wind and solar storage microgrid model for simulation and verification, proving the effectiveness of the control strategy.
    14  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](504) [HTML](0) [PDF 1.01 M](2131)
    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.
    15  Incremental current waveform analysis and lineselection faultlocation method for intermittent breakdown grounding in distribution network
    ZHOU Yixuan PI Jie SONG Tianbao ZOU Yun YANG Lili LUO Dechang
    2020, 35(4):58-65. DOI: 10.19781/j.issn.16739140.2020.04.008
    [Abstract](356) [HTML](0) [PDF 1.24 M](2071)
    Abstract:
    In order to improve the reliability of lineselection and faultlocation for singlephase grounding failures in distribution network, the current waveform at different stages were studied and stimulated. Firstly, in terms of the summarized common features of current waveforms during their development, the incremental current of the subtransient sawtooth wave in the grounding phase and the incremental current in the sound phase are selected as the criterion signal sources for the fault location of the insulation loss in distribution networks. The general characteristics of all grounding currents reflected by the saw tooth currents are analyzed. Then, the difference of waveform characteristics is analyzed between singlephase grounding current and operationinduced disturbance currents. It provides a criterion for identifying the authenticity of singlephase grounding failure. The line selection and location method are proposed for the singlephase grounding including the insulation loss to avoid misidentification. Finally, the proposed method is applied to the grounding locator in a low voltage distribution network model for verification.
    16  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](2070)
    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.
    17  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](2035)
    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.
    18  In phase change in load current monitoring method in power system research
    WEI Rui ZHOU Lixing PENG Chaomin CHEN Hao SHI Lingwei ZHOU Luping
    2020, 35(4):147-153. DOI: 10.19781/j.issn.16739140.2020.04.020
    [Abstract](361) [HTML](0) [PDF 1.02 M](2015)
    Abstract:
    When itoccurs load mutation in cophase power supply system, conventional detection method in detecting the fundamental active current and reactive current will exist a time buffer, which in turn directly affects the detection effect of fundamental active current and reactive current at power grid side. It may lead to not timely compensate the reactiveand harmonic current in load side. Based on the above problems, this paper proposed a Scott balance transformer combined balance transform device of cophase traction power supply system mode. The twophase voltage and current analysis Through the special power supply mode of the twophase balance transformer. According to the instantaneous reactive power theory of twophase circuit, the whole singlephase fundamental wave active and reactive current signals aredetected.Theactive current in the whole singlephase circuit is decomposed. Thus,the amount of negative sequence can be obtainedin the case of mutation, and then the positive sequence under the condition of fundamental wave stability is recombined with the negative sequence. Therefore, the dynamic performancegets greatly improved when it occurs load mutation. Simulation and theoretical comprehensive analysis verify the rationality of this method.
    19  An improved engineering calculation method of static voltage stability limit
    ZHAO Rui YUAN Huafang YANG Junwei ZHANG Yan ZHANG Wenchao CHANG Qiankun DONG Nan
    2020, 35(4):181-182. DOI: 10.19781/j.issn.16739140.2020.04.025
    [Abstract](345) [HTML](0) [PDF 960.60 K](1926)
    Abstract:
    Based on the analytical expression of the static voltage stability limit derived from apparent power, this paper gives an index to identify the weak point of static voltage stability, and proposes an improved engineering calculation method for the static voltage stability limit. The power system simulation software is mainly used in the project to calculate the static voltage stability. This method simulates the load growth in the stability calculation program, and solves the problem of limit misjudgment caused by the difficulty of the convergence of the operating point near the static voltage stability limit in the ordinary power flow algorithm. In the power flow calculation program, the PV node of the generator in the region is modified to a PQ node, which solves the problem of excessive output of reactive power caused by the dynamic calculation characteristic of the generator in the stable calculation program. Finally, a certain district power grid in Beijing is used as an example to verify the adaptability of the calculation method.
    20  A condition assessment method of transformers based upon the dynamic grey target with the interval grey number
    ZHOU Jingsong YU Jingfeng YANG Huanhong ZHU Binquan DING Yutao WANG Jie
    2020, 35(4):133-140. DOI: 10.19781/j.issn.16739140.2020.04.018
    [Abstract](267) [HTML](0) [PDF 919.20 K](1873)
    Abstract:
    Nowadays, the condition assessment of transformer doesn't consider the dynamic characteristics and variational tendency of information in different stages. On this background, a dynamic gray target assessment model based on approaching degrees is proposed in this paper. First of all, the index data of benefittype and costtype are standardized. Secondly, the variance and the mean deviation of the interval grey number are introduced to evaluate the data volatility of the interval index. Then, the best weight can be determined. After that, a dynamic grey target evaluation model of interval grey number is proposed considering the accumulation of transformer phase information and the dynamic variation of index. The approaching degree is regarded as the basis of condition assessment. At last, the multistage operation data of multiple transformers in a substation is analyzed to verify the validity of the proposed method.

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