01 August 2018, Volume 39 Issue 8

    

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  A “Source-Grid-Load-Storage” Cooperative Optimization Method Based on Consensus Algorithm

  ZHANG Xin, DENG Lirong, LI Jingguang, WANG Kang, CHEN Weihong, LI Jiale

  Electric Power Construction. 2018, 39(8): 2-8. https://doi.org/10.3969/j.issn.1000-7229.2018.08.001

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  The large-scale application of renewable energy and energy storage has made the power system gradually transform into a complex structure of “source-gird-load-storage”. In order to fully exploit the response characteristics of elastic load and the flexibility of energy storage, multi-agent based collaborative optimization of “source-gird-load-storage” has become increasingly important. In this paper, a “source-gird-load-storage” coordinated scheduling model is proposed, with the consideration of transmission loss. Consensus algorithm is adopted to solve the model. Numerical simulation results show that the collaborative optimization model can improve the renewable energy consumption；the consensus algorithm rapidly gives the optimal solution and has the same precision with globally optimized particle swarm algorithm.
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  Optimal Energy Dispatching Strategy for Microgrid Considering Multi-Scale Demand Response Resources

  LIU Baolin, ZHOU Shaoxiong, CHEN Yaosheng, YANG Ping

  Electric Power Construction. 2018, 39(8): 9-17. https://doi.org/10.3969/j.issn.1000-7229.2018.08.002

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  With the deepening of the power system reform, the operation mode of multi investment and centralized management has been formed in the user-side microgrid. It is of great practical significance to study the energy optimization of microgrid considering the interests of operators. In this paper, the optimal energy dispatching strategy for microgrid is proposed, which aims at maximizing the income of the operators purchasing and selling electricity and minimizing the demand response compensation cost. Considering the multi-time scale characteristics of demand response, this strategy brings two demand response resources, i.e. aggregated air conditioning and electric vehicles, into three different time scales dispatching plan （namely day-ahead, in-day, and real-time dispatch）, and optimizes the energy storage system output and demand response supply step by step to realize the global benefit maximization of the operators. Load aggregator predicts controllable capacity of load in each period and takes response dispatch in real time, on the basis of the control model of aggregated air conditioning and electric vehicles. Finally, the test results have verified the effectiveness of the proposed method.
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  Optimal Reconfiguration and Coordinated Scheduling of Active Distribution Network Considering “Generation-Grid-Load-Energy Storage”

  XING Haijun，HONG Shaoyun，FAN Hong，ZHAO Xiaoli

  Electric Power Construction. 2018, 39(8): 18-23. https://doi.org/10.3969/j.issn.1000-7229.2018.08.003

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  Aiming at the coordinated optimization problem of “generation-grid-load-energy storage” in active distribution network （ADN）, this paper proposes the day-ahead coordinated optimal operation model considering the integration of the distributed generation （DG） and battery energy storage system （BESS）. The mathematical model takes the active power loss within 24 hours as the objective. The timing characteristics of DG and BESS are considered. Multiple interval distribution network reconfiguration and BESS optimal operation are taken as the active measures for the “generation-grid-load-energy storage” coordination. The second order cone programming （SOCP） method is used to solve the model. IEEE 33-node system is selected for the verification. Different capacities of DG and BESS are analyzed for the coordinated optimization problem. The result shows that the coordination can largely decrease the active power loss and improve the system operation characteristic.
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  Optimization Algorithm and Profit Distribution of Wind-Thermal-EV Cooperative Dispatch for Wind Power Consumption Under the Alliance Theory

  SUN Bo, WANG Lu, LI Simin, LI Zhiheng

  Electric Power Construction. 2018, 39(8): 24-31. https://doi.org/10.3969/j.issn.1000-7229.2018.08.004

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  In order to promote the collaborative cooperation of multi-party entities in the power system, the rational establishment of the profit distribution mechanism among system members is of utmost importance. In view of the randomness, volatility and anti-peaking of wind power output, this paper first bundles wind and thermal power to form a stable power transmission system, and forms a major coalition of priority alliances with electric vehicles （EV）. Secondly, with the aim of maximizing profits, an optimal dispatch model under the major alliances and non-alliance models is constructed. On the basis of the profit results under different dispatch models, the Banzhaf-Owen value are used to make profits allocation among major coalitions and internal members of priority coalitions. Finally, the core theory is used to determine the possibility of cooperation among wind power providers, thermal power providers, and electric vehicle users under this allocation strategy. The example simulation results show that the joint scheduling of internal members of the Grand Alliance can promote the consumption and development of wind power. After the Banzhaf-Owen value allocation strategy is adopted, cooperation can be established, and major alliances and internal members of the priority alliance have considerable returns.
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  Coordinated Robust Optimization Strategy for Active and Reactive Power in Active Distribution System Based on Scenario Analysis

  HUANG He, REN Jiayi2, GAO Song, GU Wei, LIU Haibo

  Electric Power Construction. 2018, 39(8): 32-41. https://doi.org/10.3969/j.issn.1000-7229.2018.08.005

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  This article takes the requirement of economic and security operations of active distribution systems into consideration, and puts forward a coordinated robust optimization strategy for active and reactive power in active distribution system on the basis of scenario analysis. Firstly, a coordinated multi-period optimization model of active and reactive power based on second-order cone programming is established with the consideration of controllable resources power characteristics. Based on this model, this paper puts forward a robust coordinated optimization of active and reactive power with the consideration of reducing the negative effect of energy uncertainty on the system. By generating typical scenario sets, the robust strategy can obtain the robust control policy for the active distribution system in extreme scenarios. Numerical tests on the modified IEEE 14 distribution system show that the proposed strategy can make the system stable.
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  Economical Operation Optimization of Distribution Network Considering Multiple Adjustment Measures

  TU Hui1，ZHOU Jiancong，SHI Wenchao，GAO Hongjun，LI Xiang，LIAO Lijuan，LU Lin

  Electric Power Construction. 2018, 39(8): 42-52. https://doi.org/10.3969/j.issn.1000-7229.2018.08.006

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  Due to the strong coupling relationship between active power and reactive power in distribution network, the traditional method of optimizing the active and reactive power cannot make the distribution network operate in the optimal state of economical operation. And the uncertainties of load demand and power of distributed generation bring great challenges to the operation of distribution network. A two-stage robust economical operation optimization method for distribution network considering multiple adjustment measures, including on-load tap changer, capacitor banks, static var compensator, electrical storage system and switch reconfiguration, is proposed on the basis of the branch power flow model. And the non-linear power flow constraints are relaxed by second order cone so that the economical operation optimization model is transformed into the mixed integer second order conic programming model to solve effectively. To solve the uncertainties of load demand and power of distributed generation, two-stage robust optimization method is adopted, and the optimal robust operation strategy of each adjustment measure is obtained through the column-and-constraint generation algorithm. Finally, the validity of the proposed model is verified by IEEE 33-node system.
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  General Coordinated Reactive Power Optimization of Active Distribution Network on the Basis of Scenario Time Domain Probability

  ZHANG Hang, DING Xiaoqun, CHEN Guangyu, JI Rihua

  Electric Power Construction. 2018, 39(8): 53-58. https://doi.org/10.3969/j.issn.1000-7229.2018.08.007

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  In view of the randomness and controllability of wind power and energy storage, reactive power coordinated optimization is difficult. A scene analysis method based on time domain probability is proposed, using CURE clustering method to reduce the total scene number, and calculate the time domain probability of each scene at the same time. A coordinated reactive power optimization method which considering source, network, load, storage in active network is proposed. The active power optimization model based on the minimum power consumption of main online shopping is used to solve energy storage and interruptible load active power. On this basis, a coordinated reactive power optimization model is established. By using the multi-objective particle swarm algorithm, a 10 kV distribution line in a prefecture level city is finally taken as an example to verify the feasibility and robustness of the proposed method.
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  Multi-objective Optimal Operating Strategy of Distribution Network Considering V2G on the Basis of Grouping Method of Electric Vehicles

  MEI Zhe, ZHAN Hongxia, YUAN Jihe2 HUANG Hu, ZHANG Xi, DENG Qiang

  Electric Power Construction. 2018, 39(8): 59-68. https://doi.org/DOI： 10.3969/j.issn.1000-7229.2018.08.008

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   Disordered charging of electric vehicles and the fluctuation of distributed energy resources may do harm to the distribution network. An operating strategy of distribution network considering V2G on the basis of grouping method of electric vehicles is proposed to reduce the influence. An internal and external nested model is built on the basis of two aspects of macroscopic system and network topology. Cost of owners, standard deviation of distribution network and network losses are considered as objectives. In this model, distributed energy resources, distribution network and vehicles are optimized correspondingly. The optimal operating states can be gotten by the coordination of vehicles and the resources. To meet owners mobility needs, a grouping method based on two eigenvalues is proposed, which are the moment of starting to charge and the time that is needed to get owners expected charge state. Thus, dimensions of variate are decreased. Case analyses in four scenarios are solved by GA-PSO algorithm. The strategy is proved to ensure the benefit of owners, decrease load level, stabilize load fluctuations, abate difference of peak and valley load, improved voltage level and reduce network losses.
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  Allowable DG Penetration Capacity Calculation of SNOP-based Flexible Distribution Network

  LIANG Haishen,LI Shengwei,BAI Linquan, LIU Cong，LI Wei, XU Jian，WANG Qingbiao

  Electric Power Construction. 2018, 39(8): 69-76. https://doi.org/10.3969/j.issn.1000-7229.2018.08.009

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  The introduction of high-capacity DG into the distribution network will break through the power flow limit, and also affects the safe operation of distribution network. SNOP-based flexible distribution network provides a new way for improving the allowable DG penetration capacity. With bidirectional power regulation capability, SNOP helps to improve the bottleneck status of bus/branch in distribution network, achieves active regulation of power flow, and improves the DG penetration capacity. Firstly, this paper establishes the optimization model of DG penetration capacity in the flexible distribution network. Because of the large number of network nodes, the model belongs to high dimensional nonlinear optimization problem. Secondly, according to the actual scenario and parameter settings, the analysis is divided into three cases: 1） fixed position of DG in traditional distribution network, 2） fixed position of DG in flexible distribution network, 3） free access of DG in flexible distribution network. Next, MPGA is used to solve the problem, which can get the global optimal solution. Finally, a case of IEEE 33-bus distribution network is used for verification, the optimization result shows that the method not only helps to get the allowable DG penetration capacity, but also shows the best capacity/location scheme.
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  Power Supply Capability Evaluation of Active Distribution Network on the Basis of Contribution Stratified Sampling

  REN Jiafeng，MU Qitian，YANG Yongchun，GAO Yajing

  Electric Power Construction. 2018, 39(8): 77-84. https://doi.org/10.3969/j.issn.1000-7229.2018.08.010

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  The power supply capacity （PSC） of active distribution system（ADS） is affected by varieties of uncertain factors such as the topology of distribution network, component faults, load level and the volatility of distributed energy resources （DER）. In order to quickly evaluate the PSC of ADS, this paper first analyzes the factors those affect the medium and long term PSC, and uncertainty modeling of DER and load output is carried out. The contribution stratified sampling algorithm is used to sample and obtain representative samples. For uncertainty of component operation, network uncertainty modeling is based on line importance. Furthermore, a series of evaluation indexes are defined for medium and long term PSC. Finally, an improved IEEE 14-node distribution network is used to verify the model and algorithm proposed in this paper by comparison with traditional Monte Carlo method.
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  Optimal Capacity Planning of Hybrid Energy Storage System in Active Distribution Network on the Basis of Discrete Fourier Transform

  ZHONG Guobin, WU Tao, ZENG Jie, XIE Kaigui, WANG Chao, HU Bo

  Electric Power Construction. 2018, 39(8): 85-93. https://doi.org/10.3969/j.issn.1000-7229.2018.08.011

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  Taking into account the complementary of energy-type and power-type, this paper proposes an optimal capacity planning model of hybrid energy storage system （HESS） in active distribution network （ADN） based on discrete Fourier transform （DFT） to minimize the investment-operation cost of HESS. DFT is used to decompose the power of HESS into low-frequency component and high-frequency component. Low-frequency component is undertaken by energy-type energy storage system （EESS） and high frequency component is undertaken by power-type ESS （PESS）. Considering the influence of charge and discharge state on the lifetime of EESS, the depth of charge and discharge of EESS is calculated as well as the loss of lifetime of EESS. Actual lifetime of EESS is calculated and represent by investment-operation cost. In addition, taking into consideration the time-of-use electricity price and the difference of transaction power price, the optimal charge and discharge power of HESS and the reduction of lifetime loss of EESS are achieved. Case study is performed by use of modified IEEE 14-node distribution network and typical summer daily operation data. The results demonstrate the proposed model is correct and effective.
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  Research on Hierarchical Control in AC/DC Distribution Network on the Basis of Optimal Power Flow

  MENG Ming,ZHU Guolin, WEI Yi

  Electric Power Construction. 2018, 39(8): 94-101. https://doi.org/10.3969/j.issn.1000-7229.2018.08.012

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  Aiming at the problem that it is hard to realize operational optimization of hybrid AC/DC distribution network with only local control, this paper proposes a hierarchical control strategy with different time scales to combine local control with optimal dispatch. In a short-term scale, the first layer control enables to regulate DC voltage balance by means of coordinated control between converter stations. At the second layer, secondary voltage recovery in harsh operating condition is achieved by changing the control strategy of converter stations. As the third layer control, targeting minimum network loss and voltage offset, optimal energy dispatch system provides operation instructions for the lower control by optimal power flow calculation in a longer-term scale. Operating condition of network is improved by coordinated control between different layers. Simulation results in Matlab/Simulink show that this control strategy can realize operational optimization of network in various conditions and it does not rely on optimal energy dispatch system absolutely to remain distribution networks balance, which improves system reliability.
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  Control Strategy of Inter-linking Converter in Hybrid Microgrid Under Master-slave Control

  ZHU Yongqiang, WANG Fuyuan, ZHAO Na, JIA Lihu

  Electric Power Construction. 2018, 39(8): 102-110. https://doi.org/10.3969/j.issn.1000-7229.2018.08.013

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  This paper studies the power balance relationship and control strategy of the inter-linking converter in hybrid AC/DC microgrid in island mode under master-slave control. The main control unit bears the power fluctuation and maintain the stability of the system. The concept of capacity occupancy rate of main control unit is proposed to reflect the operation state of hybrid microgrid on both sides. According to this concept, the mathematical connection between AC and DC is established, and a partitioning control scheme for inter-linking converter is designed, which can regulate the power flow between the microgrid and achieve mutual power support between the two sides. In order to avoid the inter-linking converter switching frequently among different operation modes，hysteresis comparison is set up to improve the stability of control system. Simulation of hybrid AC/DC microgrid in PSCAD/EMTDC shows that, the control strategy of partition can realize the flexible control of the inter-linking converter and adjust the power flow between AC and DC microgrids accurately, which is helpful to realize power balance in the hybrid microgrid and maintain the stability of each sub-microgrid.
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  Risk Evaluation of Repeated Multiple Power Outages in the Distribution Network

  XU Mingming, YAO Sen, NIU Rongze, HU Bo, XU Hengbo, XIE Kaigui, ZHOU Ning, HAO Yu

  Electric Power Construction. 2018, 39(8): 111-115. https://doi.org/10.3969/j.issn.1000-7229.2018.08.014

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  This paper presents a risk identification method for repeated multiple power outages in distribution networks. First, the frequency of repeated multiple power outages in distribution networks is defined, and a risk early-warning index of repeated multiple power outages is proposed on the basis of the occurrence probability and the severity of outages. To accurately depict the impact of number of outages on the risk-warning index, a repeated power outage influencing factor is proposed for index correction. The probability of power outage is depicted by indices of equipment level, operation and maintenance level and grid structure level respectively, and the severity of power outage is depicted by the importance of outage load, complaints information of historical outages and the number of users affected by the power outage. Then, on the basis of analytic hierarchy process （AHP） and entropy method, risk-warning evaluation of repeated multiple power outages in the distribution network is carried out. Finally, according to the quantitative results of evaluation, lines with greater risk of repeated multiple power outages are identified. The analysis of three 10 kV lines of State Grid Henan Electric Power Company is taken as an example. The example shows that the proposed indices and methods can effectively evaluate the risk of repeated multiple power outages in distribution lines and identify the lines with higher risk.
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  Influence of Inverter Parameters Based on Droop Control on Microgrid Stability

  LIANG Haifeng，DONG Yue，ZHENG Can

  Electric Power Construction. 2018, 39(8): 119-127. https://doi.org/10.3969/j.issn.1000-7229.2018.08.015

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  As we all know, microgrid has a strong acceptance of new energy. Droop control is the hotspot technology to realize the coordinated operation of power supply in island microgrid, which can best embody the “plug and play” characteristic of distributed generators （DG）. However, most research in this field is focused on the network topology, while ignoring the inverters internal control structure to some extent. From the droop control strategy used in the inverter, first of all, on the basis of in-depth study of the internal structure, the paper establishes a full-structure small-signal function model. Next, the effect of the change of controller parameters （droop coefficient and voltage loop coefficient） on the system stability is analyzed quantificationally via a case. And then, the range of control parameters is determined by the root locus method to provide selection reference for the inverters. Finally, time domain simulation is used to show the effectiveness of the model and the practicability of the analysis method. The results are also proved to satisfy the stable operation and dynamic characteristics of the microgrid.
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  Fault Recovery Operation Strategy for Distribution Network Coordinating Islanding and Reconfiguration

  MA Chenxiao, LIU Yang, XU Lixiong, LIU Yang, ZHU Jiayuan, LIN Xiao

  Electric Power Construction. 2018, 39(8): 128-136. https://doi.org/10.3969/j.issn.1000-7229.2018.08.016

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  According to the operating characteristics of active distribution network, a fault recovery strategy, which can rationally coordinate the distribution network reconfiguration with isolated island partitioning, is presented. Firstly, load cutting and island partitioning are permitted by changing the constraints of traditional network reconfiguration model. Then, 0-1 state variables in constraints are used to simplify the primary model and improve calculating efficiency. Finally, the second-order cone relaxation technique is adopted to convert the original nonconvex nonlinear problem into a mixed integer second-order cone programming （MISOCP） problem, which can be solved easily. Simulation results on modified IEEE 33-bus system show the effectiveness of the strategy. Comparisons with other algorithms demonstrate the superiority and accuracy of algorithm in this paper.