01 June 2018, Volume 39 Issue 6

    

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  Electric Power Construction. 2018, 39(6): 0.

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   Optimal Planning of Supply Capacity in a Residential Distribution System Considering Integration of Electric Vehicle Charging Facilities

  HUANG Yuchun, WANG Hong, WANG Ke, WEN Fushuan

  Electric Power Construction. 2018, 39(6): 1. https://doi.org/10.3969/j.issn.1000-7229.2018.06.001

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  In recent years, Chinese government has been strongly promoting the popularization of electric vehicles （EVs） in the private sector, and requires that new residential buildings have the capability of fully accommodating charging infrastructure at the parking lots. The ever-increasing number of private EVs poses a challenge to distribution system planning. Distribution system planning aims to ensure that both conventional power demands and charging demands of EVs be reliably satisfied. Meanwhile, distribution system planning should well balance the security and economy of the system operation, to avoid unnecessary redundancy and hence waste of resources. Given this background, a mixed integer linear programming model for supply capacity planning of a residential distribution system is presented, with the travel patterns and coordinated charging management of EVs taken into account. The developed optimization model is then solved through the combined use of the linear programming method and binary search. Finally, a practical residential distribution system is employed to demonstrate the proposed method. Simulation results show that it is necessary and efficient to consider the travel patterns and coordinated charging management of EVs, and the peak demand in the residential distribution system can then be significantly reduced, as well as the security and economy of the system improved.

   
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   Power Supply Planning of Electric Vehicles Participating in Logistics Distribution Based on the Battery Charging and Swapping Mode

   

  CHANG Gong, DENG Youjun, YANG Hongming, WEN Fushuan, LAI Mingyong

  Electric Power Construction. 2018, 39(6): 7. https://doi.org/10.3969/j.issn.1000-7229.2018.06.002

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   ABSTRACT：  Considering the operation mode of battery charging and swapping stations （BCSSs） which can provide two kinds of power supply patterns simultaneously, i.e. the charging mode and swapping mode, the research on electric power supply strategy for an electric vehicles （EV） participating in logistics distribution is helpful to reduce the whole logistics cost. To accommodate the constraints of route selection, loading capacity, regular charging/discharging power, time and battery capacity, an optimal decision-making model is proposed for selecting EVs power supply modes in BCSSs by choosing the logistics distribution route, charging/swapping mode and regular charging/discharging strategy as decision variables, and minimizing the sum of fast charging costs, swapping costs, total degradation costs of the EV participating in logistics distribution as the objective. Comprehensive numerical simulations are conducted on a 33-node logistics distribution system, and the impacts of the power supply mode selection of EVs in the BCSSs are analyzed, and the characteristic of the proposed method demonstrated.

   
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   Life-cycle Economic Assessment of Ultra-fast Charging Station in China

   

  HUANG Xueqi，HE Bo， YUAN Xinmei,QU Dawei,LI Juan

  Electric Power Construction. 2018, 39(6): 15. https://doi.org/10.3969/j.issn.1000-7229.2018.06.003

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   ABSTRACT： Ultra-fast charging technology improves customers experience effectively by boosting the charging power of charging equipment. Operating economy of charging infrastructure should be chosen as a precondition for its promotion. Theoretical research on operating economy of ultra-fast charging infrastructure is carried out in this paper. The analysis on the costs and revenues structure of operating charging infrastructures is conducted and the economic model is constructed based on the theory of life cycle cost. Then the economic indexes are used to assess the operating economy. The life-cycle economic assessments of the 6.6 kW AC charging piles and the 350 kW ultra-fast charging station are calculated, compared and discussed. The research results can provide an important reference for promoting ultra-fast charging station and making relevant policies.

   
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  A Coordinated Charging Strategy for Electric Vehicles in a Distribution System with Unbalanced Three-phase Photovoltaic Power Inputs

  LIU Xunyuan, QI Feng, WEN Fushuan, FENG Changsen, WANG Lei, ZOU Bo, ZHANG Xizhu

  Electric Power Construction. 2018, 39(6): 21. https://doi.org/10.3969/j.issn.1000-7229.2018.06.004

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   ABSTRACT：  Extensive integration of electric vehicles （EVs） and distributed photovoltaic （PV） units will probably deteriorate the three-phase imbalance problem in the distribution system.  A coordinated charging strategy is presented for EVs in the distribution system with unbalanced three-phase PV power inputs. First, the charging load is modeled on the basis of the travel behavior and charging characteristic of EVs. Then, on the basis of the three-phase power flow model of distribution system, an EV coordinated charging strategy is proposed with the objectives to optimize the daily load profile and to minimize the three-phase imbalance degree in the distribution system. Relevant decision variables include the charging phase, charging power and charging time of EVs. The formulated optimization model is solved by using the adaptive genetic algorithm. Finally, a modified IEEE 33-bus distribution system is employed to demonstrate the proposed method.

   
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   Coordinated Charging and Discharging Management of Electric Vehicles Based on a Multi-function Big Data Service Platform

  YANG Wentao, WANG Lei, ZOU Bo, ZHANG Xizhu, WEN Fushuan, CHENG Min

  Electric Power Construction. 2018, 39(6): 28. https://doi.org/10.3969/j.issn.1000-7229.2018.06.005

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   ABSTRACT：  The coordinated charging and discharging management of electric vehicles （EVs） plays a significant role in improving load profiles and mitigating power fluctuation from renewable energy power generation. However, there are still some problems to be solved in the demand side, such as difficulty in enforcing dispatching tasks, inconvenience in charging and discharging, occasional interruptions of information interactions. Given this background,  coordinated charging and discharging strategies are proposed separately for the two levels, i.e., “the power distribution system （PDS） to EVs” and “the power transmission system （PTS） to PDS”. Firstly, a flexible management mechanism for “PDS to EVs” level is proposed considering numerous decentralized EVs and hence heavy computational burden. To this end, a multi-function big data service platform （MDSP） is developed for analyzing the performance of charging and discharging of EVs, with respect to time-of-use （TOU） pricing and short-term charging and discharging agreement （SCDA）. On the basis of the predicted EV charging and discharging power from the “PDS to EVs” level, a bi-layer two-stage chance-constrained programming model is then proposed for the “PTS to PDS” level, in which the optimal subjects of upper layer and down layer are the independent system operator （ISO） in the transmission system and VPPs, separately, including day-ahead and real-time dispatching. Finally, a sample power system with 87 buses, including both PTS and PDS, is attained by expanding the IEEE 30-bus power system, and then served to demonstrate the features of the proposed method.

   
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   Research on Internal Fault Diagnosis and Countermeasure of Modular Multilevel Converter Based on Half Bridge Sub-modules

  ZHENG TAO，ZHANG Zihang

  Electric Power Construction. 2018, 39(6): 42. https://doi.org/10.3969/j.issn.1000-7229.2018.06.006

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   ABSTRACT： Half bridge sub-modules （HBSM） are the basic units of HBSM-MMC （modular multilevel converter）, whose malfunction is one of the common faults in MMC. It has significance to realize the fast and correct fault diagnosis and protection，which are connected to the safe and stable operation of the system. In this paper, a comprehensive fault characteristic analysis on open circuit and short circuit fault of IGBT in HBSM is carried out. Depended on the analysis of fault characteristics, fault diagnosis strategies of IGBT open-circuit, IGBT or FWD short-circuit fault of HBSM are put forward，only needing to measure the voltage of the sub-module capacitance, without additional measuring points. The logic of the diagnosis strategies is simple, whose calculation results are merely represented by “0”, “1” and “ ∞”，and the proposed methods will not be interfered by external failures in AC and DC system. Then, the fault isolation strategy based on the redundant HBSM in the “hot standby” operation state is designed to realize reliable isolation of the fault HBSM, without locking the whole converter station. Finally, the simulation experiment in PSCAD / EMTDC verifies the feasibility of the proposed diagnosis strategies and isolation scheme.

   
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   Study on the Back-up Protection Method for Loop DC Distribution Lines Based on Polarity Discrimination

  SUN Lijing, ZHANG Hai, LIU Yinglin, LUO Guomin, WU Ming

  Electric Power Construction. 2018, 39(6): 49. https://doi.org/10.3969/j.issn.1000-7229.2018.06.007

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   ABSTRACT： Longitudinal differential protection methods applied to DC lines are widely used in transmission and distribution systems in our country because of their high reliability and good operation results have been obtained. However, with the rapid development of distributed generation in the distribution network, the threshold value is not easy to be set when high-impedance fault occurs, and the reliability of the protection action is poor. Traditional protection method for distribution network is not suitable for the ring DC distribution system. In this paper, a method of longitudinal protection based on the slope of sudden current change is proposed. First of all,  the direction of the sudden current change at both ends of DC distribution line are analyzed. Then, it is proposed to introduce the slope direction into the direction detection of the sudden current change. Using the polarity relationship of the fault current signal in the low frequency band, a backup protection method capable of accurately operating for the DC distribution line is realized. Finally, a simulation model is built in MATLAB / SIMULINK. Simulation results show that this method has strong capability free from jamming and the affection of transition resistance, and to accurately identify the fault range and to improve the backup protection reliability to a certain extent.

   
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   A Flexible Virtual Inertia Control Strategy for DC Microgrid

  ZOU Peigen，MENG Jianhui，WANG Yi，WANG Jian

  Electric Power Construction. 2018, 39(6): 56. https://doi.org/10.3969/j.issn.1000-7229.2018.06.008

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   A Flexible Virtual Inertia Control Strategy for DC Microgrid

   
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   Multi-Scenario Robust Transmission Planning Considering Correlation Between Wind Power and Load Demand

  HUANG Qihang, WANG Xiuli, QI Shixiong, FAN Jiajie, WANG Yifei

  Electric Power Construction. 2018, 39(6): 63. https://doi.org/10.3969/j.issn.1000-7229.2018.06.009

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   ABSTRACT： Increasing penetration of wind farms into the power systems has injected more uncertainties into the transmission planning and using uncertain theory to manage uncertainties has already been a focus that attracts many scholars attention. Traditional multi-scenario method is easy to take into consideration the correlation between wind power and load demand, while this approach has problem to control robustness of planning scheme. This paper presents multi-scenario robust transmission planning model considering correlation between wind power and load demand. Compared with each scenario denoting a fixed operational value in the traditional multi-scenario model, this proposed approach using an uncertain set to represent a scenario. The robustness of planning scheme can be adjusted through the budget of uncertainty when the number of operational scenarios is given. There is no doubt that this proposed method has more flexibility and adaptability than traditional multi-scenario ones. The CCG （column-and-constraint） algorithm is introduced to obtain the optimal solution. The planning model has been implemented on the modified Garver 6-bus and IEEE RTS 24-bus systems and simulation results demonstrate the correctness and efficiency of the proposed approach.

   
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   Research on Multi-layer Optimization Planning Method for Intelligent Distribution Network Considering Operational Flexibility

  MA Li，WANG Zongli，LIU Wei，ZHU Tieming，ZHAO Mingxin，CHEN Hai

  Electric Power Construction. 2018, 39(6): 71. https://doi.org/10.3969/j.issn.1000-7229.2018.06.010

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   ABSTRACT：  Development of flexible resources such as distributed generation and demand-side response have brought significant changes to the operation and control of distribution networks. The positive impacts of these flexible resources in peak load adjustment and flexible transfer in operation have not been taken into consideration sufficiently in the traditional distribution network planning. The impacts of flexible resources such as operation control methods and demand-side management on distribution networks planning are considered comprehensively in this paper, and corresponding planning model of intelligent distribution network is proposed with the aim of minimizing the total cost. The solving method and process are also put forward on the basis of the combination of differential evolution, Voronoi and Prim algorithms. Finally, a numerical example in a typical power supply area is provided to verify the proposed method, and results show that the economy of the proposed model has been improved significantly compared to traditional methods. The model can also provide new ideas for the planning and constructions of the future intelligent distribution networks.

   
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   Two-layer Programming Model Considering Reactive Power Cooperation for Distributed Renewable Energy in Distribution Network

  GUO Yanlin，LIU Junyong，TANG Yonghong，XU Lixiong，WEI Zhenbo，XIANG Yue，ZHOU Chunyan

  Electric Power Construction. 2018, 39(6): 80. https://doi.org/10.3969/j.issn.1000-7229.2018.06.011

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   ABSTRACT： The matching degree between large-scale integration of distributed renewable energy （DRE） and the existing control ability of distribution network has a great influence on the consumption of DREs. Conventionally, the planning of DREs didnt take the existing reactive power resources into account, which lowers the facility utilization. In operation, although DREs served as the voltage control measure, their consumption at a high proportion level didnt realize. Thus a two-layer model considering the existing reactive power resources will be adopted to maximize the profit of the DREs and improve the voltage quality of distribution network. Case study in the modified IEEE 33-bus distribution network demonstrates the rationality and effectiveness of the proposal.

   
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   Impacts of Cyber Contingencies on Cyber Physical Power Systems

  ZHENG Peixiang, CHEN Keren, WEN Fushuan, CHEN Bin, ZHANG Gonglin

  Electric Power Construction. 2018, 39(6): 89. https://doi.org/10.3969/j.issn.1000-7229.2018.06.012

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   ABSTRACT：  In a cyber-physical power system （CPPS）, the interaction between the power information system and the power physical system becomes more extensive and more in-depth. For the purpose of analyzing the impacts of cyber contingencies on the power physical system concerned, a dynamic interactive model is proposed for CPPS. In this model, the physical part of a radial power distribution system with distributed generators integrated is formulated as a typical differential-algebraic equation set, while the cyber part is described by an incident matrix model, with multiple types of cyber contingencies in the information transmission process considered, including data error, data mismatch and time delay. The feasibility and effectiveness of the proposed method are demonstrated by a revised version of the IEEE 33-bus radial distribution system.

   
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   Research on Clustering Analysis Algorithm Based on Adjustable Potential Index for User Power Consumption Behavior

  YANG Weihong, LAI Qingping, LAN Yu, WANG Dan, HU Qing′e, WANG Xuyang, LIU Yanru

  Electric Power Construction. 2018, 39(6): 96. https://doi.org/10.3969/j.issn.1000-7229.2018.06.013

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   ABSTRACT：  Against the background of continuous access of flexible loads, the ability and potential of users to participate in power grid regulation continues to increase, and the users power consumption behavior is clustered on the basis of  the users regulatory potential. On the basis of the peak-to-peak electricity price background, a load transfer rate model based on peak-to-peak time-of-use price is constructed on the basis of the principle of user psychology. On the basis of this model, a user-adjusted potential index based on peak-to-hour electricity price is constructed and used. The users electricity consumption behavior is used for cluster analysis, and the results are compared with traditional clustering algorithms based on daily load curves and typical load characteristics, which proves the validity and correctness of the clustering results of the algorithm. At the same time, the clustering analysis of electricity users electricity consumption behavior proves that the clustering algorithm based on the adjustment potential index has a better clustering effect.

   
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   Multi-objective Operation Optimization for Integrated Electricity and Gas Systems Considering the Accommodation Capability of Wind Power

  WANG Ke, WANG Peng, XU Yuan, LIU Weijia, WEN Fushuan, LIN Zhenzhi

  Electric Power Construction. 2018, 39(6): 105. https://doi.org/10.3969/j.issn.1000-7229.2018.06.014

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   ABSTRACT：  An integrated electric power and natural gas system, as a special example of an integrated energy system, is of great potential for promoting the accommodating capability of intermittent renewable energy generation through flexible operation of various energy carriers. However, the overall operation cost and energy transmission loss may suffer from significant changes depending on the penetration level of renewable energy sources. It is necessary to study the multi-objective optimal operation strategy for integrated electric power and gas systems considering the accommodation of wind power generation. First, a multi-objective operation optimization model is established by minimizing the operation cost, wind power curtailment and energy loss of the integrated electric power and gas system. Then, the nonlinear constraints are simplified by piecewise linearization, and the original mixed integer nonlinear planning model is then transformed into a mixed integer linear planning one. Moreover, the multi-objective optimization technique based on the augmented ε-constraint method is employed to solve the model, and the fuzzy comprehensive evaluation is employed to find the compromised optimal solution from the attained Pareto optimal solutions. Finally, an integrated and revised version of the IEEE 39-bus power system and the Belgium 20-bus natural gas system is served to demonstrate the feasibility and efficiency of the proposed method.

   
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   Grid-friendly Optimal Scheduling Method for Multi-microgrid System in Electricity Marketing Environment

  MI Shinong, ZHANG Jiancheng, GUO Wei

  Electric Power Construction. 2018, 39(6): 117. https://doi.org/10.3969/j.issn.1000-7229.2018.06.015

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   ABSTRACT： In this paper, a grid-friendly optimal scheduling method in electricity market environment is proposed formulti-microgrid system in distribution network, and a day-ahead double-layer scheduling model is established. The paper first constructs the optimization model of distribution network, which reduces the fluctuation of the injection power from transmission network and microgrids to distribution network and improves the economy of distribution network operation by optimizing the output of the microgrids as well as ensuring the proportion of renewable energy generation, so as to increase the enthusiasm of power system to accept microgrids, which is helpful to market operation and development of microgrids in electricity marketing environment. Secondly, in the microgrid layer, the randomness of solar and wind power is described with the multiple scenario technique. The microgrids and distribution network are regarded as different interest subjects and the incentive mechanism for dynamic electricity price is designed to guide the microgrid in accordance with the optimization of distribution network, so as to establish the economic and environmental optimization model of microgrids to coordinate the output of distributed generation. The simulated annealing algorithm is used to solve the model, and the simulation example verifies the rationality and validity of the model.

   
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   Control Strategies of Battery Energy Storage Systems for Mitigating Fluctuations of Wind Power Outputs

  GUO Yunpeng, WANG Xiaolei, WEN Fushuan, LI Liang, MAO Jianwei

  Electric Power Construction. 2018, 39(6): 125.

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   ABSTRACT： Integrating a battery energy storage system （BESS） with a wind farm with many wind power units could mitigate the output power fluctuations of the integrated system. Thus, it is an important issue to be addressed to develop an appropriate control strategy of BESS for effectively mitigating the fluctuations of wind power outputs and then maximizing the accommodation capability of the power system concerned for wind power integration. Firstly, the mathematical model of BESS is presented with the structure and characteristics of the integrated system taken into account. An improved control strategy is then proposed with the interactions between the current charging/discharging behavior of BESS and the state of charge （SOC） constraints at the next time slot taken into account, so as to fully make use of the BESSs capacity. And then, an optimal control strategy is developed for minimizing the over-limit probability of combined output power fluctuations from the integrated system, and a highly efficient solver, named AMPL/CPLEX, is employed to solve the optimization model. Finally, an integrated system including a large wind farm and a BESS is employed to demonstrate the performance of the proposed improved control strategy and optimal control strategy. Simulation results show that these two BESS control strategies could effectively mitigate the fluctuations of the combined output power of the integrated system.

   
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   Study on the Optimal Replacement Time of Physical Assets in Power Grid on the Basis of Grey Theory

  SHENG Meng，ZHANG Shuya

  Electric Power Construction. 2018, 39(6): 131. https://doi.org/10.3969/j.issn.1000-7229.2018.06.017

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   ABSTRACT： Equipment is the core asset of the power company, researching the lean management of equipment and the scientific economic life is of great significance to the grid investment decision. In this paper, concept of asset life cycle management and cost annuity method are used to analyze the overall cost of the equipment, and to establish the calculation model of economic equipment life. Using grey theory and actual data over the years, a prediction model G（1,1） for operating costs is established, and the post-test differential test method is used to test the accuracy of the operating cost forecast, then the optimal timing of equipment scrapping and replacement can be determined, the equipment cost can be optimized and the benefit can be maximized. Examples show that, the economic life prediction model of grid equipment based on the grey theory prediction constructed in this paper is feasible and the measurement results are more accurate. By comparing with actual service life of the equipment and analyzing the reasons for the differences, it can provide certain decision support for the technical transformation and grid planning of the power grid company.