01 September 2016, Volume 37 Issue 9

    

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  Collaborative Planning of Integrated Electricity and Natural Gas Energy Systems with Power-to-Gas Stations

  HUANG Guori，LIU Weijia，WEN Fushuan，DONG Zhaoyang，ZHENG Yu，ZHANG Rui

  Electric Power Construction. 2016, 37(9): 1. https://doi.org/10.3969/j.issn.1000－7229.2016.09.001

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  The increasing penetration of natural gas power generation and ever-developing power to gas （P2G） technology in recent years have promoted the coupling between the power system and the natural gas system than ever before. This coupling has introduced new challenges to the planning of integrated electricity and natural gas energy systems, as the existing power system planning models normally overlook the impacts of natural gas or other energy systems. Given this background, this paper studies the collaborative planning of integrated energy systems with combined heat and power （CHP） plants and P2G stations. First, the energy center concept is introduced and modeled, and in an energy center various kinds of energy conversion such as CHP can be carried out. A nonlinear model for an integrated energy system with multiple interconnected energy centers and P2G stations is next presented and linearized. Then, this paper takes the minimum overall cost as planning objectives including investment cost, operation cost and energy shortage cost characterizing the reliability of integrated energy systems, optimizes the location sizing problems of traditional generating units, CHP plants, P2G stations, gas-fired boilers, transmission lines and natural gas pipelines with using general algebraic modeling system（GAMS） -based CPLEX solver, and evaluates the reliability of the planning scheme and the benefit generated by P2G stations in promoting the capability of accommodating intermittent renewable energy. Finally, the effectiveness of the proposed collaborative planning model is demonstrated by a sample integrated energy system.
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  Operation Strategy for Residential Quarter Energy Hub Considering Energy Demands Uncertaintie

  ZHANG Huayi, WEN Fushuan, ZHANG Can, WANG Peng, MENG Jinling, LIN Guoying

  Electric Power Construction. 2016, 37(9): 14. https://doi.org/10.3969/j.issn.1000－7229.2016.09.002

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  In recent years, the popularization of combined heat and power generation and electric heating has attracted extensive attention. The main energy demands in a residential quarter are heating demands and electricity demands, and the energy hub can be used to descript the coupling relationship between the energy demand and the energy input. Given this background, this paper firstly presents a mathematical model for the residential quarter energy hub, with the combined heat and power generation and the heat pump as energy devices. Then, this paper constructs the deterministic model of the residential quarter energy hub operation optimization, and considers the charging load of electrical vehicles as a controllable load to participate in the operation optimization. Energy demands of a residential quarter are uncertain, and various decision-makers may have different risk preferences in determining optimal operation strategies. With this consideration, this paper employs the information gap decision theory （IGDT） to develop the robust optimization model and the opportune-windfalling model respectively, in order to obtain the scheduling strategy of risk-aversion decision-makers and risk-preference decision-makers. And then, this paper constructs the mixed integer linear programming model and adopts the CPLEX to solve the model. Finally, a residential quarter is employed to demonstrate the essential characteristics of the developed model and method.
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  A Mutual Information Method for Associated Data Fusion in Energy Internet

  LI Gang，YANG Liye，LIU Fuyan，YU Min，SONG Yu，WEN Fushuan

  Electric Power Construction. 2016, 37(9): 22. https://doi.org/10.3969/j.issn.1000－7229.2016.09.003

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  In the framework of a cyber-physical system, the amount of data in an energy internet needs to process is massive, and it is very difficult to extract knowledge and analyze the associated characteristics among data. Based on the mutual information （MI） theory, an information fusion structure with a‘data-characteristics-decision’three-layer framework is applied to the massive monitoring data of energy internet, and a multi-layer mode data fusion scheme is then presented. The MI method can measure the correlation between condition attributes and decision attributes and eliminate the redundant features, and then to extract rules and form knowledge. First, the MI method is used to determine the correlation degrees among massive monitored data, and extract the associated features in the procedure of data preprocessing. Then, the multi-layer feedforward neural network （MLFNN） is used for fusion of decision-making with massive data. The proposed method is then combined with the well-known MapReduce （MP） model in the field of parallel computing for large-scale data sets so as to figure out a "Mutual Information-Multiple-layer Feedforward Neural Network-MapReduce" （3M） methodological framework for the fusion of large amount of data. Finally, the output power forecasting of a wind farm is served for demonstrating the presented method, whose calculation results show that the proposed method is of better forecasting accuracy and computational efficiency, compared with the traditional variable selection method.
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  Price Guide of Electric Vehicles Charging Based on Cost Function

  TONG Xin, GUO Chunlin, ZHANG Mingzhi

  Electric Power Construction. 2016, 37(9): 30. https://doi.org/10.3969/j.issn.1000－7229.2016.09.004

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  The charging of large number of electric vehicles （EV） will affect the secure operation of power grid. In order to reduce the impact of charging load on the grid, the charging price can be adjusted to guide the charging behavior of EV owners. This paper derives the formulas of self-elastic coefficient and cross-elastic coefficient based on the cost function. And this paper establishes two time-of-use （TOU） price plans and a TOU price model for guiding EV charging with considering the motivation level of owners and the load fluctuation in power grid. Finally, this paper compares the optimal TOU prices between these two plans. The results show that TOU price can effectively guide the charging behavior of EV owners, and the increased difference between peak and valley load price will stabilize the load fluctuation in power grid and reduce the EV owners' charging cost.
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  Fuzzy Matter-Element Assessment Method of Electric Vehicle Charging Station Planning

  TAN Yangyang，YANG Honggeng，XU Fangwei，ZHANG Xi

  Electric Power Construction. 2016, 37(9): 36. https://doi.org/10.3969/j.issn.1000－7229.2016.09.005

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  The scientific and rational planning of urban electric vehicles （EVs） charging station is an important prerequisite for large-scale EVs interacting with smart grid friendly. This paper realizes the planning assessment of EV charging station based on fuzzy matter-element theory. We analyze the features of urban EV charging station, and establish the evaluation index system for alternative charging station. We adopt fuzzy-matter element analysis method to obtain the optimal fuzzy matter-element sequence with alternative points, which is taken as a reference sequence. Then, we use the entropy method to obtain the weights of alternative points corresponding evaluation index, calculate the weighted gray relational degree of alternative points through gray correlation analysis method, and determine the planning scheme of EV charging station based on the size of correlation degree. Finally, the simulation results verify the rationality and feasibility of the proposed method.
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  Charging and Discharging Control of Electric Vehicle by Electric Vehicle Agent

  LI Wenhua, FAN Xintao, KONG Meijuan

  Electric Power Construction. 2016, 37(9): 43. https://doi.org/10.3969/j.issn.1000－7229.2016.09.006

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  When large scale electric vehicle is incorporated into the power grid for power grid dispatching, a proxy mechanism needs to be set up in a certain area as the intermediary of power company dispatching department and electric vehicle. According to the control of the electric vehicle by the agency, firstly, the area is divided into the office area, residential area and the supermarket shopping area, which can be controlled by one day. Secondly, according to the state information of each electric vehicle, the electric vehicle is divided into charging cluster and discharging cluster. Thirdly, according to the scheduling capacity, the scheduling time, the evaluation system of the default degree of electric vehicle owners, the agency queues the charging or discharging order of electric vehicle in the cluster in each period. Finally, in the case of safety constraints of electric vehicle owners driving and battery, the charging and discharging scheduling for electric vehicles can make the agent meet the dispatching plan of the electric power company as far as possible.
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  State-of-Charge Estimation of Large Scale Battery Energy Storage System Based on Improved Unscented Kalman Filter

  ZHAO Zekun, ZHANG Xilin, ZHANG Bin, HAN Xiaojuan

  Electric Power Construction. 2016, 37(9): 50. https://doi.org/10.3969/j.issn.1000－7229.2016.09.007

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  Accurate and reliable state of charge （SOC） estimation for large capacity battery energy storage system （LCBESS） is necessary for the battery management system （BMS）. Since the difference between batteries, it is difficult to obtain ideal prediction results by traditional methods. To solve the above problem, this paper proposes the prediction method of SOC for LCBESS based on improved unscented Kalman filter （UKF）, which adopts the genetic algorithm （GA） method to optimize the filter coefficients of UKF, in order to further improve the prediction accuracy of SOC. This paper simulates the series battery energy storage system under setting conditions. The simulation results show that the proposed improved unscented Kalman filter method can obtain the effective and reliable prediction results of SOC, which has a broad prospect of engineering application.
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  Control Strategy of Grid-Connected PV-Hydrogen-Storage Generation

  PENG Long，CAI Guowei，KONG Lingguo，CHEN Chong，DU Jiabao，DUAN Jie，ZHANG Hao

  Electric Power Construction. 2016, 37(9): 56. https://doi.org/10.3969/j.issn.1000－7229.2016.09.008

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  Intermittent, randomness and volatility of photovoltaic （PV） power generation, has been one of the main reasons restricting its large-scale development. This paper uses pure green hydrogen energy storage devices with high energy density to improve the reliability of power supply of PV array. In hybrid systems, hydrogen energy storage devices comprise electrolyzer, hydrogen storage tank and a proton exchange membrane fuel cell （PEMFC）, etc., for each cell by bringing together the power converters to the DC bus, and finally are connected via an inverter from the AC grid. Taking into account the constraints on the limit of pressure hydrogen storage tank, the electrolyzer and the rated output of fuel cell, this paper introduces high power density supercapacitors as a backup to ensure continuous and reliable power supply and the maximum use of solar energy resources. Under the premise of satisfying the constraint conditions of each component and hydrogen energy storage device starting a higher priority than supercapacitor, this paper proposes power coordination control strategy under six kinds of operation modes, whose effectiveness is verified by simulation analysis.
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  Influence of Scaled Photovoltaic Grid-Connected System on SSO Characteristic of Thermal Power Unit

  ZHENG Chao, LI Yuan

  Electric Power Construction. 2016, 37(9): 62. https://doi.org/10.3969/j.issn.1000－7229.2016.09.009

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  Large-scaled development of photovoltaic （PV） and concentrated to power grid, is one of the important forms of solar energy resources utilization in China. The fluctuated PV power combined with adjustable conventional thermal power unit is an important way to enhance the capacity utilization efficiency of AC transmission line.In the above scenario, it is urgent to research the influence of PV on the sub-synchronous oscillation （SSO） damping characteristics of proximate thermal unit. This paper establishes the electromagnetic transient simulation model of PV power generation unit including three main parts such as battery plates, voltage source converter and control system. And then, this paper studies the influences of large-scaled grid-connected PV and its different electrical parameters on SSO damping characteristics of proximate thermal unit, such as the impedance of collective line, operating points, access location and so on.Aiming at the threat of SSO under AC transmission compensated with series capacitor, this paper proposes the suppression measure that the additional damping controller is installed into the dynamic reactive compensation device located at the PV power collection station. The simulation results verify the effectiveness of the proposed measure.
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  Principal Problems of Energy Storage Optimization Allocation

  LI Dandan, SU Xiaolin, YAN Xiaoxia, TAN Yixue

  Electric Power Construction. 2016, 37(9): 70. https://doi.org/10.3969/j.issn.1000－7229.2016.09.010

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  Energy storage optimization allocation is the foundation of energy storage system （ESS） application, which involves two dimensions of technical and economic aspects, also relates to the different needs of multi-application time scales and power energy. According to the different application requirements of ESS in power grids, focusing on security and stability, frequency regulation, acceptance of renewable energy sources and power quality, this paper analyzes the optimal allocation of its objectives, conditions, methods and theories deeply. Based on the cost-benefit analysis of energy storage system, this paper establishes a general NPV （net present value） optimization model. Combined with the application characteristics of different energy storage, this paper analyzes the selection principles of energy storage type, as well as the combination type of composite energy storage and the methods of capacity allocation. This paper presents the relevant evaluation index and methods for the evaluation of energy storage application from the compensation effect, safety, reliability, economy and so on. Finally, this paper proposes the future research topics in the practice of energy storage planning.
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  VDCOL Parameters Optimization to Improve Multi-Infeed HVDC System Stability

  LYU Sizhuo, YANG Ying, ZHENG Chao, SUN Weizhen, LI Jing, ZHANG Jing

  Electric Power Construction. 2016, 37(9): 79. https://doi.org/10.3969/j.issn.1000－7229.2016.09.011

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  In East China and South China power grid, it has formed the pattern that many HVDC transmission systems feed into the receiving-end grid. Because of the strong coupling of multi-infeed HVDC systems, AC voltage disturbance will lead to the commutation failure of multiple HVDC at the same time, even voltage instability. At first, this paper analyzes the inverter station dynamic reactive power change track of dual-infeed HVDC test systems, and reveals the mechanism that the optimization of voltage dependent current order limiter （VDCOL） parameters can reduce the total reactive power demand. According to the influence of resisting disturbance capacity of converter bus on DC power recovery characteristics, this paper proposes the optimization scheme of VDCOL parameter based on multi-infeed short circuit ratio （MSCR）. The simulation results of East China multi-infeed HVDC systems show that proposed optimization scheme of VDCOL parameter can reduce the reactive power demand of inverter station and improve the voltage stability of receiving end of power grid.
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  Reliability Research for UHVDC Transmission System with Parallel Converters

  ZHAO Zheng, MA Weimin

  Electric Power Construction. 2016, 37(9): 86. https://doi.org/10.3969/j.issn.1000－7229.2016.09.012

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  The safety and reliability operation of UHVDC projects, which are characterized by large transmission capacity and long working distance, has vital practical significance. This paper establishes a fault-tree model of UHVDC system with parallel converters, which can help to calculate the forced energy unavailability, monopole forced outage times and bipole forced outage times of UHVDC projects effectively. Then, this paper proposes several sensitivity indices which show the impact of every equipment on the reliability of UHVDC system, thus to effectively find the weak points of the project. Finally, based on the statistical data of the reliability of HVDC projects of SGCC （State Grid Corporation of China） in the past 10 years, this paper calculates and compares the reliability indices for the main wiring schemes of three different kinds of UHVDC system with parallel converters. Moreover, this paper completes the sensitivity analysis on the reliability index of system affected by equipments, and finds the key links which affect the forced energy unavailability, monopole forced outage times and bipole forced outage times. The results show that this research can determine the topology of high-reliability UHVDC system with parallel converters, and provide important reference information for the reliability improvement of UHVDC projects.
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  Integration Planning of Microgrid Considering Power Quality Constraints

  HU Pan, CHEN Hongkun, ZHU Xiaohang, CHEN Cong

  Electric Power Construction. 2016, 37(9): 93. https://doi.org/10.3969/j.issn.1000－7229.2016.09.013

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  In nowadays, the power quality problems, such as voltage fluctuations and harmonic, limit the high integration of microgrid in the distribution network. This paper innovatively proposes a method for microgrid integration considering the power quality constrains preliminarily at the planning stage. Firstly, we derive the probabilistic power fluctuation model of microgrid, and present the static-state evaluation of power quality of microgrid. Based on the consideration of network loss and other economic benefits, we transform the power quality index into the related constraint conditions, and present the chance-constrained model for microgrid integration. As the proposed model is a mixed integer one consisting of both linear and non-linear element, we adopt linear decreasing inertia weight-particle swarm optimization （LDIW-PSO） algorithm to solve it. In order to verify the proposed method, we simulate the microgrid integration in a real industrial park under IEEE 33-bus system, whose results show that the proposed method can effectively improve the permeability of microgrid in distribution network.
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  Comparison and Selection of Power Grid Planning Based on Life Cycle Cost

  LIU Liping，PENG Bo，GU Xi，LIU Sheng，CHEN Cong，LIAO Zhiwei

  Electric Power Construction. 2016, 37(9): 101. https://doi.org/10.3969/j.issn.1000－7229.2016.09.014

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  The life cycle cost of power grid assets is a key technology in power system planning to control long-term cost and short term investment. Considering the effects of reliability, economic indicators and different replacement cycleson the cost calculation, this paper proposes a cost calculation model base on LCC for transmission network to compare and select the schemes of smart grid planning. Meanwhile, in combined with the theory of power network reliability analysis and LCC theory, this paper proposes the reliability index calculation and quantitative method based on Monte Carlo model, studies the effect of different load types on reliability cost, and then establishes the LCC cost model of power grid planning with considering the replacement of equipment. Finally, this paper verifies the accuracy and effectiveness of the proposed LCC cost calculation model through an appropriately example of comparing and selecting of two planning schemes for an 110 kV substation.
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  Reliability Evaluation of Distribution Network with Distributed Generation Considering Correlations

  HU Meiyu, HU Zhijian, HU Mengyue

  Electric Power Construction. 2016, 37(9): 108. https://doi.org/10.3969/j.issn.1000－7229.2016.09.015

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  To analyze the impact of correlation between wind speed, illumination intensity and load demand, this paper proposes a new reliability evaluation model for distribution system with distributed generation （DG） considering correlation. Firstly, we adopt the correlation coefficient matrix, Latin hypercube sampling and Cholesky decomposition to establish a sampling method, which can effectively deal with the correlations between the non-normal distribution random variables and the nonlinear relationship. Then we propose the method of correcting the traditional reliability index based on island stable operation probability, which effectively combines the traditional distribution reliability assessment with the distribution reliability assessment containing DG to improve the assessment efficiency. Finally, through the quantitative analysis on examples, we analyze the influences of correlation intensity between the same type DG, different types of DG, DG and load on island stable operation and distribution system reliability index, whose results verify the feasibility of the proposed model and method.
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  Control Strategy of Virtual Synchronous Generator Based on Adaptive Droop Characteristic

  LIN Yan, ZHANG Jiancheng

  Electric Power Construction. 2016, 37(9): 115. https://doi.org/10.3969/j.issn.1000－7229.2016.09.016

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  The photovoltaic-energy storage unit, based on virtual synchronous generator （VSG） control, can be used to form island microgrid, and provide forceful support for the stable operation of microgrid. However, the imbalance between power consumption and generation in the cycle of running, will get the state of charge （SOC） of energy storage equipment beyond its safe operation region, due to the fluctuation and intermittent of distributed generator output. According to this issue, the method of adjusting droop coefficient according to SOC is introduced into the VSG control. Through analysis, it is found that it may be difficult to achieve the control target by changing the droop coefficient. During the regulating process, the system can even lose its stability. By introducing the concept of adaptive droop characteristic, further improvement of VSG control is made by translating the whole droop characteristic. The improved VSG control reduces the impact on system stability. The reasonable allocation of active power and the fast adjustment of SOC can be realized more effectively. Relevant theoretical analysis and proposed scheme are verified by the simulation system built with Matlab/Simulink simulation tool.
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  Modeling and Simulation of No-Load Cutting-In Operation Control for Doubly-Fed Induction Generator

  LAN Fei, YAO Zhiyang, LI Jinghua, TAO Li

  Electric Power Construction. 2016, 37(9): 123. https://doi.org/10.3969/j.issn.1000－7229.2016.09.017

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  This paper proposes a two-stage control scheme of ‘no load - grid connected’ to realize the smooth state transferring from ‘no load’ to ‘grid connected’, according to the characteristics of ‘no load’ and ‘grid connected’ of doubly-fed induction generator （DFIG）. Based on the Matlab/Simulink platform, we establish the simulation models of a no-load operation and a grid-connected operation of DFIG respectively, and give the simulation module and parameters based on the stator field-oriented vector control technology, which provides important basic information and platform for the research on the grid connected control technology of DFIG. Then, we propose a set of the simulation experiment scheme for ‘no load - grid connected’ DFIG, which can obtain comprehensive results for testing the control strategies. Finally, we verify the effectiveness of the proposed control strategies and simulation model, through the simulation results of the no-load operation, the transient process at the cutting-in moment, and the maximum power energy tracking （MPPT） after grid-connected operation.
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  Sea-Island Distributed Generation Planning Model Based on Godlike Algorithm

  NIU Dongxiao, MA Tiannan, HUANG Yali, LIU Bingyi

  Electric Power Construction. 2016, 37(9): 132. https://doi.org/10.3969/j.issn.1000－7229.2016.09.018

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  To achieve the effectiveness of power supply with low pollution and low cost in island area and improve the absorptive and utilization capacity of renewable energy, this paper establishes the multi-objective distributed power planning model, which includes mainly three aspects of the cost of investment, system loss and system stabilitybased on the characteristics of island distributed generation planning. Based on the concept ofPareto optimal solution, we adopt Godlike algorithm to solve the above multi-objective, multi-constrained and nonlinear optimization problem. Finally, we apply the proposed model and its solution algorithm to the practical planning problem of an island distributed generation system in South China. The simulation results showthat the Godlike calculation result is far superior to the single genetic algorithm, simulated annealing algorithm, differential evolution algorithm and particle swarm optimization algorithm, which can effectively avoid the problem of falling into local optimum and premature maturation of single algorithm in solving distributed generation planning problem and ensure the global Pareto optimal solutions.
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  Cost-Benefit Analysis of Grid-Connected Distributed Generation Considering Different Stakeholders

  LUAN Weijie,LIU Shu, CHENG Haozhong,ZHANG Shenxi,XIAO Yuanbing

  Electric Power Construction. 2016, 37(9): 140. https://doi.org/10.3969/j.issn.1000－7229.2016.09.019

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  The gradual increase of the distributed generation connected to distribution network has exerted an impact on the cost and benefit of the distributed generation and distribution network. On the basis of summarizing the current business model of grid-connected distributed generation, this paper calculates the cost and benefit of power company and independent investor after distributed generation connected to distribution network with using net present value method and payback period method. And then the paper compares the cost and benefit of grid-connected distributed generation under different business models and different load mode. The calculation results show that, in the economic aspect, distributed generations bring more disadvantage to power company under the current business models, and independent investors gain more benefit when using more power.
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  Day-Ahead Tow-Stage Dynamic Economic Emission Dispatching in Wind Power Integrated System Incorporating Demand Response

  LIU Xu, YANG Deyou, MENG Tao, ZHANG Wang, LIU Xi, JIANG Minglei

  Electric Power Construction. 2016, 37(9): 146. https://doi.org/10.3969/j.issn.1000－7229.2016.09.020

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  As an important interactive resource between generation side and demand side, demand response can effectively regulate the distribution of load demand to achieve energy-saving and emission-reduction and improve the system wind power capacity. Based on this, this paper considers the demand response in the environmental economic and proposes a day-ahead two-stage dispatching model under smart grid. The first stage is day-ahead user interaction stage, in which the next day load distribution is adjusted by time-of-use price leverage guiding the user to take rational power consumption and the optimal load curve and time-of-use price is determined by considering the load level and user satisfaction index. The second stage is day-ahead dispatching stage, in which the economic emission dispatch model is established based on chance-constrained programming for wind power randomness and this model is transformed into a deterministic model by using wind power distribution function. We propose an improved multi-objective particle swarm optimization algorithm by introducing the diversity index, random black hole theory and the multi-targeted search mechanism, and adopt technique for order preference by similarity to ideal solution（TOPSIS） method to sort the Pareto frontier individual to help the dispatcher to make scientific decision. The simulation results of the improved 10 machine system verify the validity and rationality of the model and method.