01 September 2018, Volume 39 Issue 9

    

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  Scheduling Strategy Based on MILP for Assembly Enterprises Participating in Demand Response

  QI Bing, XIA Yan, LI Bin, LI Dezhi, CUI Gaoying

  Electric Power Construction. 2018, 39(9): 1-8. https://doi.org/10.3969/j.issn.1000－7229.2018.09.001

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  There is much research on the demand response technology, but mainly concentrated in smart home appliances and intelligent buildings. Since the electricity consumption of industrial enterprises possess a very high proportion in social electricity consumption, if the demand response potential of these enterprises can be taken full advantage, it may play an important role for balancing the grid power and enhancing the competitiveness of enterprises. Production models of manufacturing and assembling enterprises are constructed in this paper. At the same time, an automatic demand response algorithm is designed on the basis of mixed integer linear programming to maximize the profit of the manufacturers. In a case study of a battery manufacturing plant, the proposed algorithm automatically meets the needs of the grid as well as increasing the manufacturers profits. And the superiority of the algorithm is specifically demonstrated through three scenarios, including peak valley price, demand side bid, new energy consumption （wind power suppression）. In addition, it describes the relationship between the potential of the assembly enterprises to participate in the demand response and the proportion of the storage tank capacity, and provides the idea for the further research of the assembly enterprise to participate in the demand response.
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  Study on the Control Strategy of Frequency Conversion Air Conditioning Considering Thermal Comfort

  HUANG Haitao，WANG Daifeng，ZHU Fengze，WANG Junwei

  Electric Power Construction. 2018, 39(9): 9-17. https://doi.org/10.3969/j.issn.1000－7229.2018.09.002

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   In recent years, with the development of frequency conversion thermostat technology, inverter air conditioner to the demand response control strategy has brought new opportunities and challenges. In this paper, a quantitative evaluation model of PMV-PPD user comfort is introduced, and a thermostatic control strategy of multi-family inverter air conditioner group considering thermal comfort is proposed, which takes into account the users comfort experience and the maximum load reduction capacity. Firstly, the optimal temperature setting of constant temperature control of inverter air conditioner is determined by user thermal comfort and the maximum reduction of air conditioning load, and the non-grouping constant temperature control strategy of air conditioning group is established. Then, the capacity of the non-grouping control and the loss of opportunity response are analyzed and evaluated for different scheduling periods. It is proposed that the chances of loss of opportunity response can be reduced by group control when the scheduling period is within a certain range, which fully exploits the demand response potential of the home air conditioning load and obtains the demand response resource which can reduce the capacity stability. Finally, an example shows that the strategy is feasible and effective.
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  Load Characteristic Analysis and Application Research on Integrated Energy System

  ZHANG Yongxin，SHEN Hong，MA Jing

  Electric Power Construction. 2018, 39(9): 18-29. https://doi.org/10.3969/j.issn.1000－7229.2018.09.003

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  Integrated energy system can achieve efficient utilization of energy, and is of great significance in dealing with resource shortage and environmental pollution. Load characteristic analysis and application research are the vital parts and working basis of design, planning and operation of an integrated energy system. Aiming at the key problems about load characteristic analysis and application raised by this paper, a research framework is established. Then, the automatic realization method of bad load data identification and correction is put forward for actual integrated energy system load data. At last, based on the research framework, the load profile and law of the system at different time scales, the feasibility of enhancing the predictability of multiple loads with different types of energy data, and the potential of the integrated demand response between power and cold load are explored. The results show that the proposed framework can fully excavate the load characteristics of integrated energy system, and will play an active role in improving the predictability of load and giving full play to the potential of integrated demand response.
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  Multi-objective Optimization Model of Regional Hybrid Energy System Compatible with Responsive Load

  WANG Tao, CUI Huaiyu, WU Geng, ZENG Ming

  Electric Power Construction. 2018, 39(9): 30-38. https://doi.org/10.3969/j.issn.1000－7229.2018.09.004

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  The construction of integrated energy system is an important way to promote renewable energy consumption, achieve multi-energy cooperation, and improve energy utilization efficiency. Considering operation cost, CO2 emission intensity and renewable energy accommodation benefits of the system, a multi-objective optimization model of regional hybrid energy system （RHES） compatible with responsive load is built. With the constraint conversion and fuzzy satisfying decision method （FSDM）, the multi-objective mixed integer optimization problem is transformed into a single objective optimization problem and then be solved. A numerical example shows that, according to the constructed multi-objective optimization model of REHS, the operation cost, emissions cost and renewable energy accommodation benefits can be comprehensive optimized. In addition, when considering responsive load, the daily peak-valley difference of the system is reduced, and the reduction targets of operation cost and emission are further optimized.
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  Impact of Pole-to-ground Faults on Transformer DC Bias and Differential Current Protection in Hybrid AC/DC Power Systems

  DAI Zhihui，SU Huaibo，WANG Xue，JIAO Yanjun

  Electric Power Construction. 2018, 39(9): 39-46. https://doi.org/10.3969/j.issn.1000－7229.2018.09.005

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  Pole-to-ground faults in the hybrid AC/DC power system may result in DC-bias voltage on the AC side of the MMC converter. If the transformer is Dyn-11 connected with small grounding resistance, the DC current caused by the pole-to-ground fault would pass the transformer and lead to DC bias in magnetic field, which would further produce the magnetizing inrush current and the malfunction of differential current protection of transformers. In this paper, with respect to YNd-11 connected transformers and Dyn-11 connected transformers with different grounding resistance in hybrid AC/DC distribution grids, the impact of pole-to-ground faults on the DC bias of transformers are analyzed. Influencing factors are subsequently concluded. Secondly, as an example of hybrid AC/DC systems, the DC-access PV grid-connection system model is established in PSCAD/EMTDC to verify the correctness of the theoretical analysis. Finally, countermeasures for DC bias, as well as the identification of pole-to-ground fault and single-phase grounding fault are given after analyzing the protection misoperation caused by DC bias.
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  Control Strategy of Unidirectional Modular Multilevel DC-DC Converter

  WANG Jian，WANG Yi，FU Chao

  Electric Power Construction. 2018, 39(9): 47-53. https://doi.org/10.3969/j.issn.1000－7229.2018.09.006

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  DC power grid is the research hotspot to solve the stability problem related to grid-connected renewable energy. DC-DC converters play the key role to connect DC grid at different voltage level. Modular multilevel DC-DC converters adopt modular topology which is suitable for high-voltage and high-power applications. The unidirectional modular multilevel DC-DC converter is suitable for voltage conversion with a certain direction of power transmission. It has low cost and simple control method. But research on this topology is still relatively less. Corresponding control strategy is still mainly following the nearest level modulation（NLM）of MMC, and there is no practical demonstration project in China. So it is necessary to study the topology more deeply and put forward the control strategy which is suitable for the topology, and provide some reference values for practical demonstration projects. A new control strategy for unidirectional modular multilevel DC-DC converter is presented in this paper. The control strategy adopts current tracking instead of traditional voltage tracking, and calculates the numbers of the inserted sub-modules at the beginning of each cycle. By controlling the switch, the output current will follow the reference current. Finally, a simulation model of unidirectional modular multilevel DC-DC converter is built. The simulation results show that the control strategy can realize the voltage transformation well and current fluctuation at the input side is small. It is an effective control strategy.
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  Research on Multi-Time-Scale Control System of DC Distribution Network

  FAN Shixiong, LIU Xingwei, WEI Zechen, GAO Yunxing, WANG Chen

  Electric Power Construction. 2018, 39(9): 54-60. https://doi.org/10.3969/j.issn.1000－7229.2018.09.007

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  With large number of new energy access and the development of power electronic technology, DC distribution network has more advantages than AC distribution network. Meanwhile, the development of DC distribution network also demands the establishment of its control system. For the DC distribution network with new energy and energy storage, a multilevel DC voltage control system based on time scale is proposed. The control system is divided by time scale of millisecond level, second level and minute/hour level. On the basis of voltage droop control, three levels of voltage control are proposed, including the primary voltage regulation and inertial control for stabilizing voltage and damping power fluctuation, the secondary voltage regulation for eliminating the voltage difference, and the third voltage regulation for optimal operation. Finally, a four-terminal DC distribution network with PV and battery is established in Matlab/Simulink for simulation. Effectiveness of the proposed control system is verified by simulation results.
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  Research on Intelligent Protection Configuration Based on DC Breakers for Multi-terminal Flexible DC Distribution Network

  XU Yutao, TAN Zhukui, XIE Baiming, HUANG Hui, LU Qiansu1 BAN Guobang, YUAN Xufeng

  Electric Power Construction. 2018, 39(9): 61-69. https://doi.org/10.3969/j.issn.1000－7229.2018.09.008

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  In order to improve the operation reliability of multi-terminal flexible DC distribution network and shorten the time of fault impact, an intelligent protection configuration scheme based on DC circuit breaker is proposed. Firstly, the typical fault characteristics of system are analyzed from the aspects of topology, converter and load types. Subsequently, after the protection area has been divided, the complete protection principle, the layered configuration and the DC line fault line selection method is developed. By cooperating with the operation logic of primary equipment and secondary control system, a protection scheme with self-switching dynamic settings, quick system recovery after fault, and accurate fault line selection is configured, which can be adapted to different operation modes. Finally, a digital simulation model of three-terminal flexible DC distribution network is built in PSCAD software and the protection response characteristics under typical failures are tested, which verifies the effectiveness of the proposed protection scheme.
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  Optimal Bidding Strategy Based on Two-Stage Stochastic Programming for Virtual Power Plant

  ZHOU Bo，LU Lin，GAO Hongjun，TAN Xinyi，WU Honghao

  Electric Power Construction. 2018, 39(9): 70-77. https://doi.org/10.3969/j.issn.1000－7229.2018.09.009

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  Considering the uncertainty of the market price and the power of renewable energy, this paper adopts virtual power plant （VPP） model to aggregate distributed energy （electric vehicles, demand response, etc.） to participate in electricity market transactions, to improve the stability and market competitiveness of VPP by optimizing and coordinating distributed energy sources. Using multi-scenario method to simulate uncertainty of day-ahead market clearing price and the output of wind power plant, with the goal of maximizing the operating efficiency, the optimal trading strategy model of VPP based on two-stage stochastic programming is formulated. In the first-stage, day-ahead market consider the uncertainty of the price；in the second-stage, balance market consider the uncertainty of the wind power plant production. In addition, the risk associated with the VPP profit is explicitly taken into account through the incorporation of the conditional value-at-risk metric, so as to realize the preference of economy and risk. Finally, the influence of risk appetite and uncertainty on the profit and risk loss of VPP are analyzed, which can provide valuable reference for different risk appetite of VPP.
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  Technical Prospect of Raiden Network in Electric Vehicle Charging Transaction

  LI Gang, HUANG Yimin, ZHENG Guping, ZHOU Guoliang

  Electric Power Construction. 2018, 39(9): 78-86. https://doi.org/10.3969/j.issn.1000－7229.2018.09.010

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  In view of the new opportunity brought by block chain ecosystem to the energy field, this paper researches the transaction scheme of electric vehicle （EV） charging. On the basis of analysis on block chain technical connotation and the characteristics of transaction, a management system of electric vehicle charging transaction based on raiden network is put forward. Through the use of smart contracts with intermediary transfer mechanism, the management channel of under-chain transaction based on raiden network is established, and gives the charging transactions between users and electric vehicles. This architecture can help reduce the transaction chain pressure, promote the transaction frequency, increase line speed, reduce management cost and operation risk in the block chain transaction network etc. Combined with the using scenario of charging piles, the process of transaction under the raiden network and the implementation process under the smart contract are explained. Finally, the expansibility and application of block chain in energy transaction management are prospected.
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  Dispatch Based on Information Gap Decision Theory for Power System with Wind Power

  PAN Zhaoxu, LIU Sanming, WANG Zhijie, WANG Shuai, DING Chaoran

  Electric Power Construction. 2018, 39(9): 87-94. https://doi.org/10.3969/j.issn.1000－7229.2018.09.011

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  With the development of society, new energy sources, such as wind power, which have randomness and intermittency, have begun to connect to the power grid. At the same time, the change of load side structure, the subjectivity of user and the limitation of prediction technology make the actual load demand difficult to be obtained accurately. These new factors have led to increased "Knightian Uncertainty " in the power system, which makes power system scheduling become a very challenging job. The paper makes use of a new non-probabilistic approach-information gap decision theory （IGDT） to model the uncertainty of wind power output and the system load demand. And two models are deduced in risk averse and opportunity seeker strategies for dispatcher, which solves the Knightian Uncertainty of wind power and load in power system. Finally, the analysis is examined on Modified IEEE 39-bus system, and the validity of IGDT model is proved by result analysis and Monte Carlo method.
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  Optimal Dispatch for Microgrids with CHP Considering EV Users Intention

  SUN Zhipan, LIU Huilan, LI Ran, CHEN Yu, HUO Qijing, ZHENG Haodong

  Electric Power Construction. 2018, 39(9): 95-104. https://doi.org/10.3969/j.issn.1000－7229.2018.09.012

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  The increasing of access number which including private electric vehicles and distributed power posed a question to microgrids with combined heat and power （CHP）. Therefore, On the basis of the microgrid model with CHP and renewable energy, considering the users intention, the electric vehicles （EVs） are modeled according to different charging and discharging behaviors selected by users. And then, a multi-objective optimization model is established including microgrids with CHP and EVs considering time of use （TOU） tariff, and it is then transformed into a single-objective model by the method of fuzzy mathematics. In the analysis of this model, four different scenes are optimized by Gurobi Solver. The rationality of model and results are verified by comparing optimization results under the four scenes.
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  Interval Economic Power System Dispatch Based on Improved TLBO Algorithm

  ZHOU Buxiang, HUANG Jianan, HUANG Zhengang, ZHANG Baifu, ZHANG Ye

  Electric Power Construction. 2018, 39(9): 105-111. https://doi.org/10.3969/j.issn.1000－7229.2018.09.013

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   In view of wind power fluctuation and the uncertainty in forecast, an economic dispatch model with standby response capacity constraint is constructed. Considering the high cost and high environmental benefits of wind power, a new balance factor named coefficient of abandoned wind is introduced in order to balance the cost of wind power, and the effective range of the balance factor are defined. At the same time, the new teaching factors and cross-operation are introduced in the teaching-learning based optimization （TLBO） algorithm, which may further improve its convergence speed and convergence ability, and the solution is applied to the model. Finally, the improved TLBO algorithm （ITLBO） is used in a 10-machine simulation system, which verifies the effectiveness of the abandonment coefficient to balance the cost of wind power and the superiority of the algorithm to solve such problems.
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  Bi-level Optimal Dispatch Model of Active Distribution Network with Demand Response

  HUA Liangliang，HUANG Wei, GE Liangjun, LIU Lifu

  Electric Power Construction. 2018, 39(9): 112-119. https://doi.org/10.3969/j.issn.1000－7229.2018.09.014

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  Active distribution network can promote effective consumption of distributed generation and ensure safe and economic operation of the system by taking advantage of demand response and coordinated optimization to guide source-load coordination. Considering the uncertainties of system, a bi-level optimal dispatch model of active distribution network is proposed. The price coordination layer, taking the price-type demand response as the core, optimizes the load demand by adjusting day-ahead electricity price. The schedulable unit control layer makes the operational plan of system according to load demand to minimize the operating cost considering the effect of uncertainties within active distribution network on the safety of system. The two layers exchange information with each other and achieve the coordination and interaction. A solution strategy combining intelligent optimization algorithm and traditional optimization algorithm is proposed to improve the solution efficiency. The results of the example show that the proposed model can ensure the safety of system, improve customer satisfaction, as well as reduce the system operating cost and peak-valley difference.
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  Multistage Linearization Probabilistic Power Flow Calculation Based on Piecewise Copula and Gaussian Mixture Model

  JIANG Xuechen, YUAN Yue, WU Han, XU Yundai, HUANG Ruanming, WANG Yuefeng

  Electric Power Construction. 2018, 39(9): 120-128. https://doi.org/10.3969/j.issn.1000－7229.2018.09.015

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  Large-scale integration of wind power into grid and load stochastic volatility increase the uncertainty in power system operation, in order to effectively analyze the system operation features in the new environment, a calculating method based on wind power piecewise Copula and load Gaussian mixture model for multistage linearization probabilistic power flow is proposed. Piecewise Copula is used to establish the spatial correlation model among wind farms on the time dimension considering seasonal variation. For non-normal and multimodal load, expectation maximization （EM） algorithm is used to establish load Gaussian mixture model, and an improved K-means clustering is proposed to optimize EM algorithm, which can simplify the modeling process. On the premise of these models, calculating probabilistic power flow in the method of multistage linearization cumulant method, fully considering the impact of wind power and load fluctuation on the system operation. The accuracy and efficiency of the proposed probabilistic power flow calculation process is verified through the test on modified IEEE 14-bus system.
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  Discussion on Frequency Control and Evaluation Concerning All Kinds of Power Disturbances

  ZHU Quansheng, CHANG Yekui, ZHANG Zhen’an, ZHAO Hua, JIN Cuicui, WU Yuqiong, LIU Rao

  Electric Power Construction. 2018, 39(9): 129-136. https://doi.org/10.3969/j.issn.1000－7229.2018.09.016

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  Frequency control has always been one of the concerns in the operation of interconnected power grid. Considering new demand of frequency control in UHV transmission system, combined with the five level dispatching management model of "Unified Dispatch, Hierarchical Management" in China power grid, the control thought that frequency control in China should be divided according to the dimensions of disturbance severity is proposed. And the performance evaluation method of disturbance control suitable to integral frequency control under high-power loss fault as well as the three level scheduling schemes for state grid, regional grid and provincial grid are designed on the basis of in-depth analysis of North American reliability standard set. The simulation results show that the performance evaluation method for frequency control of interconnected power grid concerning all kinds of power disturbances has better frequency control effect than the disturbance control method of North American. The new method can improve anti-disturbance ability effectively and is beneficial to safe and stable operation.