01 June 2020, Volume 41 Issue 6

    

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  Scheme and Method for Market Participation of Virtual Power Plant Based on Equilibrium Theory

  AN Qi， WANG Jianxiao， LI Gengyin， WANG Xuanyuan， LIU Zhen

  Electric Power Construction. 2020, 41(6): 1-8. https://doi.org/10.12204/j.issn.1000-7229.2020.06.001

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  With the depletion of fossil energy and its pollution to the environment， the environmentally-friendly distributed generation has been widely adopted. However， large-scale integration of distributed energy resources （DERs） may cause power quality problems and influence the reliable operation of power grids. The emergence of virtual power plant （VPP） effectively solves these challenges. By coordinating and optimizing DERs， a VPP can alleviate the impact of plug-and-play DERs on the bulk power grid； thereby improve the security of power grids. However， research on the coordination between VPPs and power grids still needs further investigation. Therefore， we propose a market equilibrium method in this paper， which enables an iterative coordination between VPPs and the bulk power grid until converged. First， we analyze the definition of VPP and DERs. Then， the optimal coordination between VPPs and the bulk power grid is formulated as a market equilibrium problem. A two-level mathematical model is proposed. The objectives of both VPP-level and power grid-level models are to minimize the operation costs， respecting the constraints for DERs and transmission networks. An iterative solution algorithm is designed to efficiently solve such a problem. Case studies demonstrate that the proposed model and method can effectively reduce the complexity of coordination between VPPs and the bulk power grid while considering the corresponding impacts， thus reducing the total operation costs and improving the economic level of the entire power system.
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  Two-Layer Game Model of Virtual Power Plant Applying CIQPSO Algorithm

  TAN Zhongfu，TAN Caixia，PU Lei，YANG Jiacheng

  Electric Power Construction. 2020, 41(6): 9-17. https://doi.org/10.12204/j.issn.1000-7229.2020.06.002

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  In order to make full use of the large-scale energy-storage advantages of electric vehicles （EVs） and the advantages of agent aggregators to flexibly purchase and sell electricity in the power market， to make up for the imbalance between supply and demand in virtual power plant （VPP）， this paper constructs a two-layer game model of a virtual power plant in which electric vehicles participate， to perform internal and external optimization of the virtual power plant at the same time. On this basis， firstly， a fully dynamic game model of the upper-level agent aggregator - virtual power plant is constructed to perform external optimization of the virtual power plant. Secondly， a virtual power plant - electric vehicle aggregator cooperation game model is built to optimize the virtual power plant internals， and the improved Shapley value is used to allocate the cooperation revenue between the virtual power plant and the electric vehicle aggregator. Finally， a virtual power plant with integrated wind turbines， controllable loads， energy storage batteries， users， and electric vehicles is used to analyze the example. The coevolutionary immune quantum partical swarm optimization （CIQPSO） algorithm is used to search for the optimal solution. The results of a numerical example show that the participation of electric vehicles in a virtual power plant can simultaneously improve the both economic benefits  and increase the supply-demand balance capability of the virtual power plant.
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  Dynamic Electricity Trading Strategy for Multi-Microgrid Under Transactive Energy Framework

  LIAN Xiaolin1，LI Xiaolu1，LU Yiming2，DING Yi3，LI Congli3

  Electric Power Construction. 2020, 41(6): 18-27. https://doi.org/10.12204/j.issn.1000-7229.2020.06.003

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  In order to promote electricity transaction and coordinated control among microgrids and to smooth power fluctuation between the microgrid and the distribution network， a dynamic electricity trading strategy for multi-microgrid under transactive energy（TE） framework is proposed．Firstly， the electricity transaction pattern of multi-microgrid based on transactive energy platform is designed to ensure the privacy and security of market participants and improve the flexibility of electricity transaction．Secondly， a dynamic electricity trading model for multi-microgrid is established．The first objective is to optimize electricity price by minimizing the cost of the microgrid taking into account the cost of energy storage battery degradation and controllable load dispatch compensation．The second objective is to optimize electricity transaction by minimizing the total electricity trading cost of multi-microgrid．Then， coordinating electricity transaction among microgrids based on multi-round auction aims to promote supply-demand balance and reduce the power interaction between the microgrid and the distribution network．Finally，the effectiveness and economics of the proposed strategy are verified by three interconnected microgrids．
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  Bi-level Bidding Strategies for Virtual Power Plants Considering Purchase and Sale Risks

  YE Fei1， SHAO Ping1， WANG Xuanyuan2， ZUO Juan1， WANG Jun3， DOU Xun3， ZHANG Xin3

  Electric Power Construction. 2020, 41(6): 28-35. https://doi.org/10.12204/j.issn.1000-7229.2020.06.004

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  Virtual power plant is a new generation of intelligent control technology and interactive business model that aggregates and optimizes the generation-grid-load-storage clean development. Aiming at the interactive influence of internal resources of the virtual power plant and the external market on the bidding strategy， considering the bilateral interaction characteristics of the virtual power plants internal resources and the external market， a bi-level power price-volume bidding model of the virtual power plant with internal resources and external market is established. Taking into account the price uncertainty of the external market， the conditional value at risk （CVaR） is used to quantify the risks in the purchase and sale of virtual power plants， and a bi-level multi-objective bidding model for virtual power plants with the risk of purchasing and selling electricity is established. Finally， the validity of the bidding strategy is verified using a numerical example.
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  Modeling of Virtual Power Plants Based on Ubiquitous Interconnection Participating in Real-Time Market

  ZHAO Chen，HE Yujun，LUO Gang，GONG Chao，ZHAO Yue，ZHANG Xuan，CHEN Qixin

  Electric Power Construction. 2020, 41(6): 36-43. https://doi.org/10.12204/j.issn.1000-7229.2020.06.005

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  With the deployment of internet of things （IoT） platform， a massive number of flexible resources at demand side can be aggregated into a virtual power plant （VPP） with ubiquitous interconnection and involved in the power market trading by providing demand response， so as to mitigate the peak demand of power system. For the need of instantaneity， dispersion and autonomous coordination of VPP members in the real-time trade， this paper proposes a real-time energy market model adapted to the participation of VPP， and adopts a distributed dispatch method based on the coordination between users and edge nodes， for the objective of offering proactive demand response. In this method， the VPP allocates the bidding power to edge nodes using a projective function based on aggregate capability of each edge. Then， edge node and users compute and interact the responsive power iteratively using an alternating direction method of multipliers. Finally， a practical case study is conducted in order to verify the effectiveness of the proposed algorithm. The results show that the method can meet the need for VPP in providing instant and efficient real-time response.
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  Modeling of EV Charging-Swapping-Storage Integrated Station

  HU Jue， WEI Gang， YUAN Hongtao， LUO Zhigang

  Electric Power Construction. 2020, 41(6): 44-51. https://doi.org/10.12204/j.issn.1000-7229.2020.06.006

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  The electric vehicle （EV） charging-swapping-storage integrated station （CSSIS） is an electric vehicle centralized integrated energy storage and power station that integrates charging stations， power conversion stations and cascade energy storage power stations， which can reduce system power fluctuations. This paper proposes a model of electric vehicle CSSIS considering fast charging station， battery swapping station and cascade energy storage station. Firstly， according to the behavior characteristics of fast-charging users， a model of EV fast charging station is established. Secondly， on the basis of speed-flow practical model of city roads， a model of EV battery swapping station is established. Finally， combined with the cascade energy storage model， an integrated electric vehicle CSSIS model is constructed. Taking the actual road conditions of bus lines in a city into account， a case verifies that the integrated station model proposed in this paper can meet the demand of electric vehicle charging load， and has the advantages of reducing the daily total operation cost and suppressing power fluctuation.
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  Network Loss Evaluation of Power Systems Considering Participation of Electric Vehicles in AGC

  LIU Hui， XIE Liangfeng， XIE Haimin， YANG Yude， QIN Zhijun

  Electric Power Construction. 2020, 41(6): 52-59. https://doi.org/10.12204/j.issn.1000-7229.2020.06.007

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  In this paper， a network loss evaluation method for power systems is proposed to analyze the influence of large-scale electric vehicles （EVs） integration on system network loss， considering the participation of EVs in automatic generation control （AGC）. While constructing the framework on electric vehicles participating in AGC control， available capacity of EVs for regulation at each node is estimated according to EVs information such as charging/discharging power， and the nodal power distribution method considering the participation of EVs in AGC is proposed. Besides， the system network loss is modeled with EVs participation in AGC. Finally， taking the IEEE 118-node system as an example， the results show that， compared with the generator sets participating in AGC control， EVs participating in AGC control is more conducive to maintain the system network loss at a certain level without wind power， and has a greater impact on the system network loss with wind power.
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  A Charging Coordination Method for Distributed Charging Piles Considering Local Voltage Amplitude and Cloud-Edge Collaboration

  CHEN Mingqing，LI Jianlin

  Electric Power Construction. 2020, 41(6): 60-68. https://doi.org/10.12204/j.issn.1000-7229.2020.06.008

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   In order to solve the problems of harmonics， load peak-valley difference and network loss caused by centralized charging of a large number of charging piles in the distribution system， a coordination method for decentralized charging piles on the basis of local voltage amplitude and cloud-edge collaboration is proposed. Under the cloud-edge-end power Internet of Things architecture， firstly， using the history information on voltage amplitude of each end device （charging pile） to analyze the maximum power consumption information of each charging pile； then， through the edge computing ability of edge nodes （distribution and transformation terminals） in the power Internet of Things， collecting the data of charging piles and combining the user preference， energy cost and the historical route of electric vehicles. Finally， in the Hadoop cloud platform， the deep belief network （DBN） algorithm is used to train and predict the future load data， and the target optimization model is established. In addition， the performance of the proposed method in different scenarios is compared with that of the centralized charging coordination method. The experimental results show that the proposed method realizes the coordinated and orderly charging of a large number of decentralized charging piles， reduces the load fluctuation and the impact of charging load on the power grid.
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  Control Method of Large-Scale Battery Energy Storage System for Suppressing the Disturbance of Power Grid

  JIA Xuecui 1， LI Xiangjun 1， WAN Jun 2， LI Wenqi3， HUO Fangqiang2

  Electric Power Construction. 2020, 41(6): 69-76. https://doi.org/10.12204/j.issn.1000-7229.2020.06.009

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  In order to meet the demand of power grid regulation， this paper proposes an optimal control method for large-scale battery energy storage to suppress the disturbance of power grid. According to the balance relationship among grid frequency， voltage， active power and reactive power， this paper firstly establishes a power control model of large-scale battery energy storage system considering the battery state of charge constraints. The control model includes measurement filtering， gain， dead zone， control and other complete links. On this basis， the frequency-modulation and voltage-regulation control model of large-scale battery energy storage suitable for grid regulation is derived. According to the regulation requirements of power grid and battery energy storage system with different capacity， the improved response-curve method is applied to optimize the control parameters in the model， so as to improve the flexibility and adaptability of the control system. Software PSASP is used to verify the effectiveness of the optimal control method of large-scale battery energy storage to suppress the disturbance of power grid. The results show that the system frequency can be controlled between 49.8~50.2 Hz and the bus voltage can be controlled between UN±10%UN using the proposed power control method when the grid frequency and voltage are abnormal due to large power disturbance.
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  Summary of Research on Grid-Side Energy Storage Technology

  LI Jianlin， LI Yaxin，ZHOU Xichao

  Electric Power Construction. 2020, 41(6): 77-84. https://doi.org/10.12204/j.issn.1000-7229.2020.06.010

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  Grid-side energy storage is an effective means of operation regulation， which provides a flexible guarantee for the security and stability of the power grid. With the high penetration of new energy and the rapid development of UHV power grids， grid security issues such as system fluctuations are becoming increasingly serious. In the power grid， a high proportion， widely existing， and wide-area collaborative energy storage model needs to be constructed. Therefore， it is of great significance to carry out technical research on energy storage on the grid side. This paper introduces current situation of research on grid-side energy storage technology and commercial demonstration project； summarizes methods for grid-side energy storage in site selection and optimization allocation； analyzes the demand of grid-side energy storage through theory and time-series indicators； expounds the optimization allocation technology and economic evaluation parameters in energy storage； and points out the difficult problems in promoting the application. Finally， the paper gives suggestions and prospects for development in grid-side energy storage technology， which has certain reference significance for exploiting the value in energy storage applications and innovating energy storage application business model.
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  Cost Sharing of Distributed Photovoltaic Power Generation Considering Carbon Footprint and Transactions

  HE Houyu1， HE Huaqin1， WANG Qian2， WANG Yanming1， GAO Lingjun1， LUO Zhao2， ZANG Haixiang3

  Electric Power Construction. 2020, 41(6): 85-92. https://doi.org/10.12204/j.issn.1000-7229.2020.06.011

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  With the gradual reduction of subsidies for distributed photovoltaic power generation and the advancement of unsubsidized parity on-grid， the profitability of distributed photovoltaic power generation projects has gradually decreased， which has discouraged the enthusiasm of investing in distributed photovoltaic power generation projects on the power generation side and slowed down clean power generation and distributed energy construction. The carbon emissions of distributed photovoltaic projects are tracked over the entire life cycle， and typical distributed photovoltaic power generators such as photovoltaic power generation prosumer （PPGP） are covered in carbon trading， which expands cost sharing ways of power generation. In a cost-sharing game model of distributed photovoltaic power generation， by using the MOEA / D-DRA algorithm to achieve the equilibrium solution of decision-making volume， the optimal distribution of power generation costs is realized on the generation and consumer sides. The example shows that carbon trading can effectively increase the revenue on the power generation side. When PPGP adopts preferential measures for nearby consumers， it is necessary to consider the double impact of carbon price discounts and electricity price discounts on the cost recovery period of power generation.
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  Coordinated Control Strategy for AC Fault Ride-through of MMC-HVDC Island Power Supply System

  SHEN Baoxing1， LIN Lin1， DONG Qian2， TANG Cong3， JIANG Shouqi2， XIN Yechun2

  Electric Power Construction. 2020, 41(6): 93-99. https://doi.org/10.12204/j.issn.1000-7229.2020.06.012

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  In order to solve the power imbalance problem of island VSC-HVDC links operating in parallel with AC line when the AC line is out of operation due to a fault， according to the analysis on grid-connected and the island operation control strategy of the island power supply system， a virtual synchronous control based AC fault ride-through coordination control strategy for MMC-HVDC island power supply system is proposed to realize power coordination in self-consumption and non-self-consumption scenarios. Aiming at the self-consumption scenario， a method for MMC power transfer control is proposed， which reduces the power shortage of the system only by increasing its output power， and can effectively reduce the influence range of unbalanced power. Aiming at the non-self-consumption scenario， a coordinated control strategy for MMC and wind farms to participate in unbalanced power regulation is designed to control the MMC to work at the maximum power output， and the power adjustment capability of the wind turbine is used to compensate for the remaining power deficit through over-speed load-shedding to maintain the power balance of the island system. Finally， the effectiveness of the proposed coordinated control strategy is simulated and verified. The results show that the strategy can realize the smooth transition of island power supply system from grid-connected to island operation， and can effectively improve its safe and stable operation capability.
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  Restoration Sequence Decision-Making for Smart Distribution System Considering Multiple Sources Coordination

  LIU Jiayu，MA Jiajun，WANG Ying，XU Yin

  Electric Power Construction. 2020, 41(6): 100-106. https://doi.org/10.12204/j.issn.1000-7229.2020.06.013

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  When a serious outage occurs in distribution system due to extreme events， some local resources such as distributed power sources and energy storage systems can be coordinated to restore critical loads and enhance resilience. In order to change the distribution system from fault state to restoration state quickly and smoothly， it is necessary to optimize the switching operation sequence. This paper proposes a restoration operation sequence decision-making method for smart distribution systems considering multiple sources coordination. The problem is modeled as a mixed-integer linear program which can be solved by the mature commercial optimization solver to determine the optimal switching operation sequence and system operating status after each operation. The objective is to serve more critical loads as fast as possible considering their priority. The unbalanced three-phase power flow constraints， operation constraints and in-process switch operation constraints are considered. The effectiveness of the proposed method is validated by numerical simulation with the modified IEEE 13-node test system and the modified IEEE 123-node test system.
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  Day-ahead Optimized Economic Dispatch of CCHP Microgrid Considering Wind Power Uncertainty

  CHEN Xi， XU Qingshan， YANG Yongbiao

  Electric Power Construction. 2020, 41(6): 107-113. https://doi.org/10.12204/j.issn.1000-7229.2020.06.014

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  Distributed renewable energy accounts for a high proportion in combined cooling， heating and power （CCHP） microgrids. Wind power generation has brought challenges to the optimal scheduling of CCHP microgrids for its randomness and fluctuation. In this paper， by minimizing the expected operating cost of the system， an optimized economic dispatch model of CCHP microgrid considering wind power uncertainty is established. On the basis of the truncated versatile distribution model to accurately describe the uncertainty of wind power output， the back-scene reduction technology is used to obtain a typical wind power scene after generating a wind power scene by Monte Carlo simulation method. An example of a park in Tianjin is used to analyze energy storage device working status， wind abandonment and energy shortage， and microgrid operation economy. The results verify the necessity and economy of taking into account the uncertainties of wind power by using the truncated versatile distribution model in the economic dispatch of microgrid optimization.
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  Design Optimization of Converter Valve Thyristor for New Generation of ±800 kV/8 GW UHVDC Project

  YANG Yong， SHE Zhenqiu， SONG Shengli， LI Ming，WANG Jialong，FAN Jichao

  Electric Power Construction. 2020, 41(6): 114-122. https://doi.org/10.12204/j.issn.1000-7229.2020.06.015

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  The new generation of standardized ±800 kV/8 GW UHVDC transmission projects puts forward the higher requirement on performance and reliability of thyristors used in converter valves. The performance requirements of converter valve equipment are analyzed. Then the optimization objectives of performance parameter of thyristor products are determined. On the basis of the research and development of thyristors in past projects， the optimization design and process improvement methods are studied in order to further improve current performance， reduce on-state voltage drop， improve dynamic parameter consistency and safety margin. For the new generation of standardized ±800 kV/8 GW UHVDC transmission project， two kinds of domestic 8.5 kV/5 500 A thyristors were designed and their performance characteristics were compared by special tests. The research and test results show that after the optimization design， lower on-state voltage drop and better current performance of the two thyristor products are realized， and the dynamic parameter consistency and safety margin is further improved. The two thyristor products can meet the requirements of the new generation  of standardized UHVDC project.