01 January 2017, Volume 38 Issue 1

    

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   Optimal Selection of Electrical Connecting Nodes of Electric Vehicle Charging Stations in Distribution Systems

  GUO Jianlong, WEN Fushuan, YUAN Jun, LYU Haohua, YU Zheren

  Electric Power Construction. 2017, 38(1): 1. https://doi.org/10.3969/j.issn.1000－7229.2017.01.001

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   The optimal sitting and sizing problem of electric vehicle (EV) charging stations has been studied in many existing publications for achieving spatially coordinated distributions of EV charging loads as well as other objectives. However, the determination of electrical connecting nodes of EV charging stations in a distribution system has not yet been investigated, and is the subject of this paper with the impacts on power flow considered. First, the distributions of initial charging states and starting charging time points of EVs are attained based on the fitting results of traveling statistics, and a probability model for describing EV charging loads is established and then solved by Monte Carlo simulations with demonstration of actual data of electric taxis in Shenzhen. Then, based on the percentages of bus voltage deviations and branch loss increments, a comprehensive evaluation index is employed for assessing the impacts of EV charging stations on power flow in the distribution system concerned, and the electrical connecting points of EV charging stations in the distribution system are then optimally determined. Finally, a modified version of the IEEE 33-node distribution system is served for demonstrating the proposed method.

  
  
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   Temporal and Spatial Stochastic Distribution Characteristics of Charging Loads of Electric Taxis

  LIAO Binjie, YANG Jun, WEN Fushuan, LI Bo3, LI Liang, MAO Jianwei

  Electric Power Construction. 2017, 38(1): 8. https://doi.org/10.3969/j.issn.1000－7229.2017.01.002

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  With the development of electric vehicles (EVs), the temporal and spatial stochastic distribution characteristics of EV charging are imposing challenges for power system secure and economic operation. Given this background, this paper proposes a systematical method for analyzing the charging load of electric taxis considering the temporal and the spatial stochastic distribution characteristics. First, driving patterns of electric taxis are discussed on account of typical passenger trip characteristics and the influences of two charging operation modes, i.e. fast charging and battery swapping. Then, the urban area of a given city is divided into several traffic zones by road map grid divisions, and the corresponding geographical coordinates are thus determined. Based on the grid-based traffic network, mathematical models for describing the driving, destination and path selection of electric taxis and charging/swapping behaviors are next presented, and the Monte Carlo simulation method is employed for attaining the solution. Finally, the operation scenarios of electric taxis in Hangzhou city are employed to demonstrate the essential features of the proposed method; specifically, the daily charging loads of electric taxis are investigated, and the impacts of two charging operation modes on the temporal and spatial distribution characteristics of electric taxi charging loads are compared.

   
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   Optimal Planning of Electric Vehicle Fast Charging Facilities in Urban Areas

  LI Jiayi， ZHANG Honggang， XIA Xue， NING Kanghong， PENG Mingwei， CHEN Huimiao， HU Zechun

  Electric Power Construction. 2017, 38(1): 17. https://doi.org/10.3969/j.issn.1000－7229.2017.01.003

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   This paper proposes a fast charging facility planning method in urban areas which aims to minimize both the construction and operation costs. Firstly, we divide the maps including the plan area into equal squares. Secondly, the mathematical model of planning is formulated with considering the traffic flow in each square area, the land using fee, the candidate sites of charging facilities, the capacity charge for charging stations, the costs of fast chargers and the penetration rate of electric vehicles. The constraints of the model include the service radius, the power and energy capacity requirements. Finally, we take the area within the fifth ring of Beijing as example to simulate the charging facility planning and analyze the results.

   
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   Performance Analysis of Communication Networks in Large-Scale Charging and Swapping Stations of Electric Vehicles

  GUO Yunpeng, YE Xiaming, ZHAO Junhua, WEN Fushuan, LI Bo, LI Liang, MAO Jianwei

  Electric Power Construction. 2017, 38(1): 23. https://doi.org/10.3969/j.issn.1000－7229.2017.01.004

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   The automation degree of charging and swapping station of electric vehicles is bounded up with the performance of its communication network. A well-performed communication network is the precondition of transmitting data in time and implementing the functions of automatic control and management. Therefore, the data transmission characteristics in the communication network of large-scale charging and swapping station and the communication performance are worthly studied. Firstly, this paper analyzes and models various data in communication network of charging and swapping station in detail. Then, aiming at the condition whether the data in the network sets priority, this paper carries out numerical simulations with using software OPNET and obtains a series of conclusion. The simulation results show that setting priority tags for different kinds of data is helpful for guaranteeing the reliable transmission of important data. Moreover, if the code rate of video monitoring data is high, a communication network with a broader bandwidth or even a proprietary network for these data only may be demanded.

   
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   A Reduction Method of Large Power Systems for Electromagnetic Transient Simulation and Its Application in China Southern Grid

   

  KANG Yi,LU Shaoqi, CHENG Lingyun, CHENG Gaihong,XU Zheng

  Electric Power Construction. 2017, 38(1): 31. https://doi.org/10.3969/j.issn.1000－7229.2017.01.005

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   To reduce the computational complexity of electromagnetic transient simulation program for large-scale AD/DC system under the unbalanced faults in AC system, this paper proposes a method that adopts the support strength of generators for dynamic equivalent. According to the topology of low-voltage network with 500 kV trunk network buses and whether there are generators in it, three reduction schemes are used to replace the corresponding low-voltage network. Then, the dynamic parameters of equivalent generators are obtained by a time domain aggregation method. Finally, three indicators are defined to evaluate the equivalent system. This paper carries out equivalent calculation for the planning data of China Southern Grid in 2020, and compares the steady power flow, short-circuit current level and transient response characteristics of trunk network before and after the equivalent. The comparison results show that, the proposed equivalent method can not only ensure the steady power flow of trunk network before and after the equivalent, but also ensure the short-circuit current approximately unchanged; the equivalent system greatly simplifies the original system while the characteristic of dynamic response remains.

   
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   Conventional HVDC Power Regulating Method to Improve New Energy Integration Capability (Ⅰ): Method Introduction

   

  SUN Yujiao, ZHOU Qinyong, XIA Yi, SONG Wenqin, ZHANG Zhongdan

  Electric Power Construction. 2017, 38(1): 39. https://doi.org/10.3969/j.issn.1000－7229.2017.01.006

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   The conventional HVDC transmission mode of transmitting relatively constant power is not good for the development of new energy. Since there is a long distance and there are different climate conditions, load properties and power grid operation conditions between the two power grids connected by HVDC, if it can determine the appropriate DC transfer power according to the new energys fluctuations and the operation conditions of the two power grids, it can improve the consumptive ability of new energy, and the safety and economy of system operation. Based on this, this paper proposes the regulating method of conventional HVDC power for accepting large-scale new energy. The basic idea is that, in the planning period the HVDC power curve and the two power grids generation schedules are coordinately determined according to the new energy generation power prediction and the power systems actual operation conditions with considering multiple time scales refinement, which makes DC power follow the planning. While in the real time, according to the power fluctuations of new energy, the power forecast errors and the operating conditions of the two power grids, it can achieve the real-time regulation of DC power to deal with the large random fluctuations and large forecast errors of new energy power and other emergencies.

   
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   A Sub-Synchronous Oscillation Mitigation Method by Blocking Sub-Synchronous Components in Control Loop of HVDC

  CAO Chengsha, XIAO Xiangning, ZHANG Jian

  Electric Power Construction. 2017, 38(1): 49. https://doi.org/10.3969/j.issn.1000－7229.2017.01.007

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   To mitigate sub-synchronous oscillation (SSO) of thermal power transmitted by high voltage direct current (HVDC) transmission, this paper studies a method for blocking the sub-synchronous frequency component in HVDC control  loop and designs the parameters. By mechanism analysis, this paper investigates the damping sensitivity in the sub-synchronous interaction path. The results indicate that in the pass-band (10~20 Hz) of HVDC rectifier side, the damping is the most sensitive to the triggering angle. Based on the analysis, this paper proposes a band-stop filter blocking method in the link of triggering angle generation to directly and effectively eliminate the sub-synchronous frequency component.Then, we adopt PSCAD/EMTDC to construct the electromagnetic transient simulation model for a real system, carry out time-domain simulation and damping scanning based on complex torque coefficient method, and use Prony analysis to extract the modal oscillation characteristics. The results show that band-stop filter blocking method with different parameters can significantly improve electrical damping near the modal frequencies and suppress SSO problem effectively. Compared with supplementary sub-synchronous oscillation damping controller (SSDC), the proposed method has stronger damping ability. According to the analysis results, this paper presents the optimal parameters of engineering suggestions. The comparison results between the dynamic process of the DC voltage and current with and without mitigation show that the proposed method has little effect on the normal operation and control of HVDC.

   
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   Spatial Load Forecasting Based on Fuzzy Rough Set Theory with Spatial and Temporal Information 

  XIAO Bai，LIU Qingyong，FANG Longjiang，YAO Di，SONG Kaihao

  Electric Power Construction. 2017, 38(1): 58. https://doi.org/10.3969/j.issn.1000－7229.2017.01.008

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   Spatial load forecasting (SLF) is a basic work in the field of city network planning, however, most of the SLF is based on historical load data at present, but ignores the factors of spatial information which has the impact on the SLF. For the same kind of land use type, the development degree of each district is different due to the different geospatial information, and the load density of each district is not the same. If the uniform load density is used to predict, it will inevitably bring larger of the error. Therefore, this paper proposes a SLF method based on fuzzy rough set theory and spatial-temporal information. We use geographic information system (GIS) to obtain the spatial information of the power supply community, and analyze the influence of spatial information on the distribution of each load. Then based on fuzzy rough set theory we obtain the unified fuzzy rough factors for the development of each power supply community (which are suitable for the comparison of the same type community, because unified fuzzy rough factor defined for each type of community has its own standard). Thus, we can depict the difference of load density between similar loads. The proposed method can describe the unbalanced and uncoordinated development of the load more accurately and improve the accuracy of SLF. Finally, the practicality and validity of the proposed method are verified by engineering example.

   
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   Short-Term Power Load Forecasting Based on ‘Layered-Confluence’ Model

  LEI Jingsheng,HAO Jiawei, ZHU Guokang

  Electric Power Construction. 2017, 38(1): 68. https://doi.org/10.3969/j.issn.1000－7229.2017.01.009

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   In view of problems that the electrical characteristics of power consumers have not been fully shown in short-term load forecasting and the accuracy of load forecasting is not enough, this paper proposes a new ‘layered-confluence’ model. Firstly, we layer the power consumers based on electrical characteristics, obtain the load characteristic curve of each layer with different electrical characteristics of power consumers, and take the load characteristic curve of layer as attribute factor to construct total load curve. Then, we train the model according to  real time load data and load characteristic curve of each layer confluence on different days. Finally, we implement the regression prediction. Taking the actual power load data of a region as an example, we forecast load based on the proposed prediction method. The results show that, the short-term power load forecasting method based on ‘layered-confluence’ model is superior to general regression forecasting method in 3 evaluation indices of mean absolute percentage error (MAPE), root-mean-square error (RMSE) and Pearsons correlation coefficient, which verifies the validity of the model. The ‘layered-confluence’ model has a good forecast effect through using different algorithm combination in ‘layered’ period and ‘confluence’ period, which verifies the robustness of the model. ‘Layered-confluence’ mode can improve the precision of load forecasting, which can provide a new idea for the short-term power load forecasting.

  
  
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   Monthly Electricity Forecast Based on X-12-ARIMA Seasonal Decomposition and Annual Electricity Correction

  ZHANG Qiang, WANG Yi, LI Dingrui, ZHU Wenjun

  Electric Power Construction. 2017, 38(1): 76. https://doi.org/10.3969/j.issn.1000－7229.2017.01.010

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   Monthly electricity forecast is the basis for the planning department of power grid corporation to arrange the operation and purchase plan. This paper presents a method for forecasting monthly electricity consumption considering various economic factors. First, we adopt the X-12-ARIMA  model to decompose the economic data and monthly electricity data into seasonal part,  and adopt stepwise regression analysis to study the correlation and regression model between the economic factors and electricity consumption and get the primary forecast results. Then, we use polynomial fitting to forecast the annual electricity, and use the result of annual electricity to adjust the monthly electricity consumption. Finally, we adopt autoregressive integrated moving average (ARIMA) model to correct the seasonal forecast for the months which are obviously influenced by meteorological factors and holidays, and obtain the monthly electricity forecasting model with good precision. In this paper, monthly electricity consumption from May 2014 to April 2015 in Guangdong Province are forecasted by economic data and monthly electricity consumption from March 2009 to April 2014 to obtain the average prediction accuracy of 97.78%, which verifies the effectiveness of the prediction model.

  
  
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   Coordinated Operation Strategy of Storage Battery SOC and Smoothing Wind Power Fluctuation

  SHAO Lihua, ZHANG Zhuyao, ZHANG Chunlong, ZHAO Qing， HUANG Guoping, YAN Fei

  Electric Power Construction. 2017, 38(1): 84. https://doi.org/10.3969/j.issn.1000－7229.2017.01.011

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   Using battery energy storage system (BESS) to smooth wind power fluctuation can optimize wind power output characteristics and improve the stability of output power in wind farm. In order to extend the service life of BESS, it needs to control the state of charge (SOC) of BESS in a defined interval furthest, which can have enough capacity to charge and discharge at next moment and bring a better smoothing effect. Therefore, this paper proposes a new control strategy which consists of two control algorithms. The selection between these two algorithms is determined according to the value of wind power fluctuation during the operation of system. Two algorithms are switched with each other based on the actual operating conditions of wind farms. Simulation results show that, compared with the traditional low pass filtering, the new strategy not only has a good stabilizing effect but also can make the SOC of BESS in a reasonable range which can largely extend the service life of BESS and save the cost of energy storage investment.

  
  
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   Distribution Network Power Supply Capability Assessment Method Based on Sensitivity Analysis 

  ZHANG Yu, HE Di, CAO Yu, GUO Chuangxin, GAO Shi， GAN Ning

  Electric Power Construction. 2017, 38(1): 89. https://doi.org/10.3969/j.issn.1000－7229.2017.01.012

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   Distribution networks power supply capability (DNPSC), which reflects the current power supply margins, is a significant index to evaluate the operation state of distribution systems. The traditional maximum load multiple method is limited by heavy-loaded equipment, because all buses share the same increasing ratio and the calculation will be stopped once one constraint works while using the repeated power flow (RPF) algorithm. Therefore, the DNPSC cannot be known accurately. To solve these problems, this paper proposes a load increasing mode (LIM) and an improved repeated power flow (RPF) algorithm, which is based on sensitivity analysis (SA) of equipment power flow and buses voltage to load increasing, to calculate the DPNSC precisely. The novel LIM can adopt the SA results to reduce the influence of load increasing on the load flow of heavy equipment and bus voltage deviation; the improved RPF algorithm can provide a solution when the constraints work. The example shows that the proposed LIM and improved RPF algorithm have more accurate assessment capability, which has the referencial value for the distribution networks operation and construction.

  
  
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  Small Signal Stability Analysis of AC/DC Hybrid Microgrid Under Isolated Island Operation

  XIANG Yang, FU Ming, ZHANG Aifang, DOU Xiaobo,JIAO Yang, YANG Yeqing

  Electric Power Construction. 2017, 38(1): 96. https://doi.org/10.3969/j.issn.1000－7229.2017.01.013

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   Compared with pure AC microgrid, AC/DC hybrid microgrid has many advantages, which has become a hot topic. When AC/DC hybrid micro-grid is disconnected with power grid and under isolated island operation, because that each distribution generation (DG) is power electronic interface, the system inertia is small; and the AC side and the DC side are coupled to each other through the main converter, the unstable side is bound to affect the other side, so the small signal stability problem becomes more complex. This paper establishes the model for AC/DC hybrid microgrid which including DG, energy storage, load and main converter, then finds out the systems main oscillation mode and its damping ratio, corresponding state variables through eigenvalue analysis. The proposed method can change the parameters of a particular element to improve the damping ratio in low damping oscillation mode by root locus analysis. Whats more, it effectively improves the stability of the system, and the small-signal analysis results are verified through time-domain simulation.

  
  
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   Optimal Operation Scheme and Benefit Analysis of Wind-Hydrogen Power Systems

  YANG Jingang，LIU Weimiao， LI Shunxin,DENG Tianhu，SHI Zhiping，HU Zechun

  Electric Power Construction. 2017, 38(1): 106. https://doi.org/10.3969/j.issn.1000－7229.2017.01.014

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   To improve the utilization of wind power in power grid with high penetration of renewable sources, this paper studies wind-hydrogen power system, constructs a mixed integer programming model with considering the randomness of wind power output, and proposes the new mode of wind power absorption on the spot. The model takes the maximum revenue of the wind-hydrogen power system as target and takes into account the following performance of the combined output of wind farm and hydrogen energy storage system. Combining with the actual design example, we use the simulation of the stand-alone operation of wind farm to verify the effectiveness of hydrogen energy storage system, where revenue increases by 27%. And we test the influence of electrolyzers and fuel cells capacity on the system.

  
  
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   Pollution Emission Reduction and Factor Influence Effect Analysis for Energy System Under Complex Conditions

  LIU Zhengping, LI Wei, Zhen Jiliang, WU Chuanbao, HUANG Guohe

  Electric Power Construction. 2017, 38(1): 116. https://doi.org/10.3969/j.issn.1000－7229.2017.01.015

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   Scientific energy system planning is beneficial to relieve the contradiction between energy   supply and demand  at present stage. However, the energy system consists of multiple complex subsystems, which contains a variety of uncertainties, and there are complex interactions among subsystems. With considering energy, economy and environment, this paper constructs an energy system planning model, based on uncertain optimization methods including interval programming, two-stage stochastic programming and chance constrained programming. In addition, this paper carries out sensitivity analysis of the model  optimization results  based on factorial analysis method, selecting main factors affecting pollution emission and revealing its influence and potential interaction. The model can effectively deal with pollutant emissions under complex conditions, optimize the allocation of system resources, and promote the adjustment of energy structure. The results show that on the basis of meeting the system operation and energy demands, it can effectively reduce the system cost, promote the pollution and emission reduction, and achieve the win-win of energy development and environmental protection.

   
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   Assemment and Influential Factors Analysis of Power Energy Efficiency Based on New Energy Industrial Orientation

   

  LIN Li, ZHOU Peng, ZOU Lanqing

  Electric Power Construction. 2017, 38(1): 123. https://doi.org/10.3969/j.issn.1000－7229.2017.01.016

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  The improvement of power energy efficiency is contributed to sustainable and green development of social economy. Firstly, this paper establishes the principle of selecting energy efficiency assessment indices. On the basis of the existed used assessing indices, the assessing indices of power energy efficiency oriented by new energy have been established from the three aspects of energy technology efficiency, energy economic efficiency and energy environment efficiency.The standardization law of Min-max is used to normalize the indices, and the assessing model of power comprehensive energy efficiency is established according to expert opinion and analytic hierarchy process (AHP). Taking a real regional power system as an example, its energy efficiency is assessed and analyzed, the main factors that influence the regional power energy efficiency, and the improvement space arised by those factors are both analyzed. At last, the measures and recommendations are proposed to improve the power energy efficiency. 

   
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   Flexibility Analysis of Conventional Generation with Random Fluctuation Renewable Energy

  WANG Ying, LIN Youkuo, LAN Xiaoming, ZHAO Hongshan

  Electric Power Construction. 2017, 38(1): 131. https://doi.org/10.3969/j.issn.1000－7229.2017.01.017

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   Flexibility reflects the ability of dealing with change of supply and demand in power system under a certain time scale. Flexibility study has a great significance on the analysis of renewable energy access problem. So it is needed to analyze the restrictive relationship between renewable energy and conventional generation. According to the characteristics of the ramping rate, this paper proposes the quantitative indices of the unit flexibility and the conventional generation flexibility of power system, and presents the corresponding calculation processes by Monte Carlo algorithm. Compared with other flexibility indices, the proposed flexibility indices can evaluate the flexibility of every conventional unit in power system and analyze the contribution of each one to conventional generation in the face of flexibility. Meanwhile, the ability of absorbing renewable energy also can be calculated. Finally, we take the IEEE 9-generator and 57-bus system as an example to calculate the proposed flexibility indices, and obtain the flexibility of unit and the ability of absorbing renewable energy of power system. The results show that the proposed indices are accurate and effective.

   
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   Large Consumer Direct-Purchasing Mechanism and Its Application in Northwest Power Grid Considering Renewable Energy Consumption

   

  ZHANG Xiaodong, YANG Tingtian, REN Jing, WU Zechen, ZHANG Qianwen, WANG Xiuli, YANG Hao

  Electric Power Construction. 2017, 38(1): 139. https://doi.org/10.3969/j.issn.1000－7229.2017.01.018

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   With the development of large consumer direct-purchasing and the  difficult  situation of renewable energy  accommodation , this paper proposes the mechanism of large consumer direct-purchasing with considering renewable energy consumption, and presents the suggestions for promoting the new energy consumption from  the aspects of the direct-purchasing incentive mechanisms of large consumer participating in peak load regulating, the generation right exchanged of autonomous power plant and renewable energy bundling transaction. Taking Ningxia and Gansu of Northwest power grid as examples, this paper verifies the feasibility of the proposed direct-purchasing incentive mechanisms through the example simulation calculation analysis. The proposed direct-purchasing incentive mechanisms connecting large consumer direct-purchasing with new energy consumption, which has reference significance for the development of large consumer direct-purchasing in the region with rich new energy.

   
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  Operation Strategy of Time-of-Use Electricity Price for Demand Side Considering Output Uncertainty of Grid-Connected Distributed Energy Resource

  LU Hai，PENG Xiaotao，ZHANG Bin，ZHOU Jicheng，CHEN Xiaoyun

  Electric Power Construction. 2017, 38(1): 144. https://doi.org/10.3969/j.issn.1000－7229.2017.01.019

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   Aim to the integration of distributed energy resource (DER) to distribution network, this paper studies the optimal operation strategy of time-of-use  electricity-price to improve the operation characteristics of distribution network connected with DERs. Firstly, we study the user load demand response model to time-of-use electricity-price based on load transfer rate. Then, through studying the division method of load peak valley time, we establish the operating cost benefit model for distribution network consuming the uncertain output power by DERs. Combining with the fuzzy chance constrained theory, we propose the optimal strategy of time-of-use electricity-price with considering the uncertainty of grid-connected DERs. On this basis, we further study the solving method for the time-of-use electricity-price optimal model based on particle swarm optimization algorithm. Finally, we verify the feasibility of the proposed operation optimization model for electricity price by simulation. The simulation results show that the demand-side time-of-use electricity-price operation can not only improve the DER consumption ability of distribution network, but also is beneficial to improve the comprehensive operation benefits of distribution network operation.