01 January 2018, Volume 39 Issue 1

    

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   Coordinated Optimal Dispatch among Generation and Loads in Industrial Microgrids with Controllable Loads

  LIN Jianxi, SHI Junyi, WEN Fushuan, LI Li, QIAN Feng, XIANG Liling

  Electric Power Construction. 2018, 39(1): 1. https://doi.org/10.3969/j.issn.1000－7229.2018.01.001

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   ABSTRACT： In recent years, microgrids with renewable energy generation as well as combined heat and power systems (CHPs) have been widely applied in many industrial fields due to favorable economic and environmental characteristics. Some loads in an industrial microgrid are flexible and controllable, which can be employed as a kind of potential dispatchable resources. In the operation of an industrial microgrid, how to fully employ these controllable loads and implement coordinated optimal dispatch among generators and loads are the key to improve the operation efficiency of microgrids and promote the accommodation capability of renewable energy generation. Given this background, a framework of a CHP embedded industrial microgrid is first presented, with multiple kinds of controllable loads and renewable energy generation included. Then, detailed models of three kinds of controllable loads, namely industrial manufacturing devices, heat ventilation and air conditioning (HVAC) and electric vehicles (EVs), are formulated respectively. On this basis, an optimization model with an objective of minimizing the energy cost in an industrial microgrid is developed and then solved through the CPLEX commercial solver. Finally, a case study is conducted in a typical industrial microgrid to demonstrate the feasibility and effectiveness of the proposed model.

   
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   Electrical Energy Acquisition Strategy for Load Aggregators Considering Combined Uncertainties of Distributed Generation Outputs and Electricity Market Prices

   

  YU Min, NI Linna, FANG Peng, LIU Fuyan, WEN Fushuan

  Electric Power Construction. 2018, 39(1): 10. https://doi.org/10.3969/j.issn.1000－7229.2018.01.002

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   ABSTRACT： With the ever-increasing penetration level of renewable energy generation and electric vehicles in power system, new participants in electricity market operation, the number of uncertainty factors in power system operation and electricity market transactions is increasing and hence each load aggregator (LA) has to address emerging problems and even challenges. In seeking a profit maximization solution, the LA could make full use of demand side resources in purchasing electrical energy from the day-ahead electricity market, so as to mitigate the negative impacts of these uncertainty factors and hence control the costs caused by risks. Firstly, distributed generation (DG) outputs and day-ahead market prices are formulated as variables within respective intervals. Secondly, a robust bi-level optimization model for electrical energy acquisition from day-ahead electricity market, with the objective of maximizing the profit of each LA, is presented with DG and demand response included. Finally, a modified IEEE 33-bus distribution system is employed to demonstrate the feasibility and efficiency of the proposed method.

   
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   Measurement and Analysis of Impacting Factors for Operation and Maintenance Costs in UHV Substations

  ZHOU Hongyu, XUE You, LIU Zuoyu, SHEN Jie, YU Min, WEN Fushuan

  Electric Power Construction. 2018, 39(1): 19. https://doi.org/10.3969/j.issn.1000－7229.2018.01.003

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   ABSTRACT： The operation and maintenance (O&M) of ultra high voltage (UHV) equipment is a key business issue in management and operation of a power system, identification, measurement and analysis of the factors impacting on O&M costs are essential for controlling the O&M costs effectively. Given this background, the indirect and direct impacting factors on the O&M costs of UHV equipment are first identified from both the compositions of the maintenance costs and the external environment, and parts of impacting factors are quantified by employing the dimension reduction method, decade depreciation method, fuzzy C-means clustering method. Then, these impacting factors are measured and analyzed through the correlation analysis, proportion analysis, principal component analysis, and path analysis. Finally, an actual O&M project of an UHV substation in Zhejiang province is served for demonstrating the presented method, and some important impacting factors on O&M costs are then identified.

   
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   Optimization Approach of Energy Storage System Locating and Sizing Considering Distribution System Resilience

  YANG Huoming, XU Xiaoyuan, YAN Zheng

  Electric Power Construction. 2018, 39(1): 19. https://doi.org/DOI： 10.3969/j.issn.1000－7229.2018.01.004

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   ABSTRACT： The large-scale outages with tremendous economic losses due to the increasingly frequent happening of extreme natural disasters draw more and more attention. In order to improve the capability of distribution system to endure disasters, this paper proposes an energy storage system (ESS) planning-operation two-stage stochastic optimization approach considering the resilience of distribution network. The ESS locating and sizing programming model is proposed to minimize the summation of investment cost and the conditional value of risk (CVaR) of the operation cost with taking the effects of extreme events into consideration. The scenario analysis algorithm based on Monte-Carlo simulation and forward selection in wait-and-see clusters (FSWC) is adopted to model the uncertainty of renewable energy output, load fluctuation and line outage contingencies, and the solving algorithm of ESS locating and sizing programming is established. Taking the IEEE 33 nodes system as test system, the optimization results verify the correctness of the proposed method and its improvement for distribution network resilience compared with traditional risk neutral planning method. Finally, the relationship between the investment cost and operational risk is also discussed, which can provide valuable guidelines for the planning decision of power grid corporation.

   
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   Reactive Power Compensation of Power Grid Based on V2G Reactive Power Dispatching

  ZHANG Kai,YIN Zhongdong,YANG Xiaotian,YAN Zhuowu,HUANG Yongzhang

  Electric Power Construction. 2018, 39(1): 41. https://doi.org/10.3969/j.issn.1000－7229.2018.01.005

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   ABSTRACT： The design capacity of electric vehicle (EV) charger is increasing, but the low utilization rate of itself as well as its capacity still exists, which makes reactive power compensation for grid via EV V2G technology have a potential application. This paper proposes a V2G reactive power compensation utilization mode under a two-layer dispatching between power grid and charging operator. The reactive power-voltage regulation compensation is carried out by using the remainder capacity of the charger with the ordered charging mode. The upper layer is responsible for the overall dispatching and calculation by the grid and the lower layer is responsible for the coordinated response of the charging operator to the user. Finally, a variety of working conditions are simulated and analyzed, the results show that the proposed compensation mode can effectively improve the voltage amplitude of low voltage node, reduce all-day-period average voltage deviation, and effectively restrain additional network loss caused by EV charging.

   
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   Bi-Level Optimization Strategy of Electric Vehicle Charging Based on Electricity Price Guide

  HU Dequan, GUO Chunlin, YU Qinbo, YANG Xiaoyan

  Electric Power Construction. 2018, 39(1): 48. https://doi.org/10.3969/j.issn.1000－7229.2018.01.006

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   ABSTRACT： This paper establishes a bi-level optimization model for electric vehicle charging based on electricity price guide. In the upper model, the variance of the total load of the power system is minimized by optimizing the dispatching plan of the aggregator in each period. In the lower model, the aggregator guides the users to adjust the charging plan by setting the charging price, to coincide with the upper dispatching plan. We use genetic algorithm to solve the model iteratively. The results show that, compared with disordered charging, the variance of the total load of the system decreases obviously and the fluctuation of the system is reduced after the optimization of the charging load of electric vehicle. It is proved that the proposed optimization model can achieve the dispatching of the system in upper layer and the autonomous response of electric vehicle in lower layer.

   
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   Multi-Families Electricity Energy Control and Management Strategy for Load Aggregator 

  HUANG Haitao，ZHU Fengze，LI Xiaoyu，WANG Yan，ZHAO Wenhui

  Electric Power Construction. 2018, 39(1): 54. https://doi.org/DOI： 10.3969/j.issn.1000－7229.2018.01.007

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   ABSTRACT： Load aggregators  can integrate many water heaters and air conditioners as demand response (DR) resource, and through the direct load control (DLC) participate in the bidding market demand. This paper studies the LA for more electricity energy control and management strategy. First of all, based on the water heater and air conditioning load thermal dynamic model and the single machine control cycle, taking temperature variation parameters and characteristic temperature difference as characteristics and balancing the dispersibility of thermodynamic parameters, we use clustering analysis and Gaussian distribution method to propose the grouping strategy of the water heater and air conditioning group control strategy. Then, we establish the controllable capacity prediction model of multi-family DLC according to the characteristics of each control cycle. In the end, according to the control of multi-family water heater and air conditioners, we construct the model to minimize the actual reduction of load and the deviation of the scheduling plan, so as to maximize the interests of the LA. Numerical example results show that the proposed control strategy can fully exert much DR to the potential of water heaters and air conditioners, reduce the total load fluctuation of controlled electric appliance, improve LA profits, and has the characteristics of small number of groups, simple control mode and easy operation.

   
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   Islanded Control Strategy of Micro-Grid  Based on Weight Control Method

  HE Yaqing,WANG Weiqing,WANG Haiyun, FAN Xiaochao, CAO Lingling,CHEN Yan

  Electric Power Construction. 2018, 39(1): 61. https://doi.org/10.3969/j.issn.1000－7229.2018.01.008

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   ABSTRACT： When a microgrid operates in the islanded mode, droop control method is usually used. However, in case high electric power quality is required, an increase or decrease in grid load could easily result in an unstable transient response in frequency of the microgrid system, the change in busbar voltage, serious distortion of output current of distributed generation, and the fluctuation in inverter output power, or even a breakdown in the system. To address these harmful condition, this paper firstly analyzes droop control strategy and proposes a weight control strategy, and then analyzes the impact of improved control strategy on the stability of microgrid. Finally, the simulation is carried out on the Matlab platform, and the results show that the proposed control strategy can improve the stability of the system better when the load changes.

   
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   Frequency Stability Characteristics and Control Strategies for Chuanyu Transmission Network after Asynchronous Interconnection 

   

  ZENG Jian, YE Xi, QU Xiaobin, JIN Jianke, WEN Yunfeng,ZHAO Rongzhen

  Electric Power Construction. 2018, 39(1): 68. https://doi.org/DOI： 10.3969/j.issn.1000－7229.2018.01.009

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  ABSTRACT：  After Chuanyu power grid asynchronously interconnected with Sanhua and Northwest power grids, the bipole block of a large capacity ultra high voltage direct current (UHVDC) would cause a huge power surplus to Chuanyu power grid, which would cause a dramatic frequency increase in the sending endand even result in frequency instability and system splitting. It is urgent to study the influence of UHVDC block fault on the Chuanyu sending grid's frequency stability and the corresponding control strategy under asynchronous interconnection. Based on the peak load scenario of Chuanyu grid in 2020 after asynchronous interconnection is used for simulation and analysis, with considering primary frequency modulation characteristic, this paper studies the frequency stability of Chuanyu grid following a monopolar/bipole block of one of the four major large capacity UHVDC links (Xiang-Shang, Bin-Jin, Jin-Su, and Ya-Jiang). Then, the corresponding DC modulation, special protection system and coordination control strategies to maintain the frequency stability of Chuanyu power grid are proposed. Simulation results demonstrate the effectiveness of the proposed control strategies.

   
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   Network-Reconfiguration Scheme Based on Node Search

  WENG Yixuan, ZHAO Jie, CHENG Renli, LIU Dichen, XU Junru, ZHANG Shengfeng, HE Xiaofeng

  Electric Power Construction. 2018, 39(1): 76. https://doi.org/DOI： 10.3969/j.issn.1000－7229.2018.01.010

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   ABSTRACT：  The modelling method based on line break state for complex power system network-reconfiguration has the problems that the dimension of optimization problem is too large and searching the target network may result in redundant results. Aiming at these problems, this paper proposes a modelling method with taking node recovery or not as state variable. The method takes the nodes in the power system as the search object, and obtains the unique sequence of recovery nodes through optimization. The target network can be obtained by connecting lines between those recovery nodes selectively, which meets the conditions of constraint, namely topological connectivity, safe and stable operation constraints. Meanwhile, according to the drawback of existing method for network connectivity assurance, this paper proposes a target network selection method based on Dijkstra algorithm, and verifies the validity of the proposed method with taking IEEE 118-bus system and a regional power grid as examples.

   
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   Voltage Control Partitioning Method for Active Distribution Network Based on Electrical Distance Matrix Eigenvalue Analysis

  LU Lingzhi, GENG Guangfei, JI Yuqi, LI Xiulei, WEI Zirui

  Electric Power Construction. 2018, 39(1): 83. https://doi.org/DOI： 10.3969/j.issn.1000－7229.2018.01.011

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   ABSTRACT： In view of the shortcomings of the existing voltage control partitioning methods in determining the partitioning number, this paper proposes a partitioning method based on the analysis of electrical distance matrix eigenvalues. The method is applied to the active distribution network (ADN) partitioning, which can obtain the optimal partitioning number by analyzing electrical distance matrix eigenvalues. Firstly, we use the Newton-Raphson method to calculate power flow, obtain the voltage/reactive power sensitivity matrix, and process it to obtain the augmented voltage/reactive power sensitivity matrix. Then, we define the electrical distance according to the augmented voltage/reactive power sensitivity matrix, and obtain the electrical distance matrix. Besides, we establish an index describing the eigenvalues sequence of the electrical distance matrix as the basis to determine the number of the larger eigenvalues, which is the partitioning number. At last, we use agglomerate hierarchical clustering algorithm based on Ward distance to cluster the electrical distance matrix and obtain the partitioning results. Case simulation is given to prove the effectiveness and reasonability of the proposed method.

   
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   Reserve Dynamic Zone Partitioning Method Based on Semi-Supervised Clustering Considering Wind Power

  LIU Yang，YAN Zheng，MA Hongyan，XU Xiaoyuan

  Electric Power Construction. 2018, 39(1): 90. https://doi.org/10.3969/j.issn.1000－7229.2018.01.012

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   ABSTRACT： With the continuous access of new energy and the increasingly complex structure of the power grid, the operating state of the power system is complex and changeable. The spinning reserve calculation method based on fixed zone partitioning is unable to effectively deal with the volatility of the source-network-load and the resulting congestion transmission problem. Firstly a energy and reserve co-optimization unit commitment is studied. Secondly congestion transmissions are evaluated considering wind power uncertainty and N－1 contingency. Then, taking the power transfer distribution factor (PTDF) of congestion line as similarity measure, partition iterative method is proposed based on semi-supervised spectral clustering. Finally, reserve capacity configuration is determined based on the result of dynamic zone partitioning. This paper use a 39 bus system and a 118 bus system separately for simulation. The result shows that the proposed reserve dynamic zone partitioning method can automatically determine the number of zone partitioning and is reasonable to reserve partition；the zonal reserve could guarantee the delivery of spinning reserve.

   
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   Dispersed Wind Farm Locating and Sizing Considering Wind Power Consumption and Power Flow Balance

  XU Peidong，FANG Hualiang，HUANG Shuo

  Electric Power Construction. 2018, 39(1): 99. https://doi.org/10.3969/j.issn.1000－7229.2018.01.013

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   ABSTRACT： Based on the severe wind curtailment situation and promising development trend of dispersed wind farm, this paper proposes a multi-objective dispersed wind farm planning method. The power flow entropy is introduced to describe the balance degree of system flow, and the planning objective is to minimize both the overall operation cost and power flow entropy. This paper applies Latin hypercube sampling (LHS) to deal with the uncertainty and correlation of wind speed and load, and uses the chance constrained programming to restrict the curtailment rate and power rationing after establishing the static constraint model of traditional power system. Besides, an intelligent optimization algorithm is employed in wind farm locating and sizing, the influence of different factors on planning result is studied as well. The simulation of IEEE 9 system shows that the proposed method can guarantee the economic benefit and wind power utilization, and makes the power grid more adaptable to load changes. The result also indicates the great impact of unit climbing and wind speed correlation on the planning capacity of wind power.

   
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  Power Angle Transient Stability Analysis and Inertial Control Strategy for Power Generation System with Controlled Inertia

  ZHANG Xiangyu，WANG Shuang，WANG Yi，FU Yuan

  Electric Power Construction. 2018, 39(1): 106. https://doi.org/10.3969/j.issn.1000－7229.2018.01.014

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   ABSTRACT： The variable speed wind turbines with virtual inertia can improve the system frequency stability, and the power angle transient stability of the power generation system will undergo significant changes due to the change of controllable inertia. Firstly, this paper derives the mathematical model of the interconnected two-regional power grid with wind power at both ends. By theoretically analyzing the influence of wind turbines inertial adjustment on the interconnected system transient energy in two-regional power grid, the system power angle transient stability level is evaluated. Then, for improving the adverse effects of the wind power inertial control on the system power angle transient stability, this paper proposes a variable virtual inertia control strategy of doubly fed induction generator (DFIG) based on transient energy. By rapidly adjusting the inertias at both sides of two-regional power grid, it not only can avoid the power angle instability caused by fast inertial response after failure, but also improve the transient stability of the system. Finally, a simulation model of two-regional interconnected system with high wind power penetration is established to verify the effectiveness of the proposed control strategy.

   
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   A Unified Carbon Emission Benchmark for Fossil-Fueled Units and Its Effect on Carbon Emission Reduction in Carbon Market

  LIU Kaicheng, SUN Jiagan, ZHOU Renjun, HE Guixiong, GUO Bingqing

  Electric Power Construction. 2018, 39(1): 113. https://doi.org/10.3969/j.issn.1000－7229.2018.01.015

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   ABSTRACT： To enhance the competitiveness of low-carbon units in fossil-fueled power industry, a unified emission benchmark of emission allocation for all fossil-fueled units  is put forward, including conventional coal-fire units, carbon capture coal-fired units and gas-fired units. A model aimed at minimizing the total cost of both fuel and carbon emission is built to allocate electricity among various fossil-fueled units in the future. Then, the influence of both carbon capture coal-fired power generation ratio and future carbon price on the comprehensive cost and carbon emission of thermal power industry is analyzed. In the end, proper advice is given for the realization of the carbon emission reduction goal in China.

   
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   Evaluation and Forecast of Electrified Railway Influence on Wind Farm

  DING Fanfan, ZHANG Dahai,LIU Hui, HE Jinghan

  Electric Power Construction. 2018, 39(1): 119. https://doi.org/10.3969/j.issn.1000－7229.2018.01.016

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   ABSTRACT： Based on the analysis of the negative sequence characteristics of the traction load and the impact of the negative sequence on the operation of wind farm, this paper presents a method to quantitatively evaluate the influence of electrified railway on wind farms, and calculates the critical electrical distance from the wind farm to the PCC (point of common coupling) from the practical angle. The regional power grid that electrified railway and the wind power access are equalled as the two-port network. It uses the superposition principle to calculate the negative sequence voltage and current of the wind farm on-grid point when there are several traction substations accessing to the same superior substation. The shortest electrical distance of the wind farm is calculated with taking the PCC three-phase voltage unbalance to the limit of national standard as the boundary condition, in which the wind farm is not affected by negative sequence components. Finally, an example is given to verify the effectiveness of the proposed method.