01 October 2016, Volume 37 Issue 10

    

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  Optimal Operation of AC/DC Hybrid Microgrid Based on Coevolution Improved Black Hole Algorithm

  DI Kaili, LI Xinming, LI Peng， XU Shaojun, SUN Jian

  Electric Power Construction. 2016, 37(10): 1. https://doi.org/10.3969/j.issn.1000－7229.2016.10.001

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  AC/DC hybrid microgrid can take complementary advantage of both AC and DC, and its optimal operation is an important research topic in area of microgrid. This paper establishes a mathematical model for the optimal operation of AC/DC hybrid microgrid with comprehensively considering economic cost and environmental cost. Based on the coevolution theory and the structural characteristics of AC/DC hybrid microgrid, a complicated optimization problem is split into two relatively independent simple problems: AC area optimization problem and DC area optimization problem. And an improved black hole algorithm is proposed to settle this optimal problem by the introduction of chaos mechanism, the inertial and velocity constraints of stars as well as improvement on the generation of initial stars. The simulation results show that the proposed coevolution improved black hole algorithm is suitable for the optimal operation problem of AC/DC hybrid microgrid with myriad and complex variables, and the better operation strategy can be reached at comprehensive operating cost as low as possible in this model, which verifies the effectiveness of the proposed algorithm.
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  Power Control of Interlinking Converter in AC/DC Hybrid Microgrid

  XIE Wenchao，ZHU Yongqiang，DU Shaofei，XIA Ruihua

  Electric Power Construction. 2016, 37(10): 9. https://doi.org/10.3969/j.issn.1000－7229.2016.10.002

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  According to the AC/DC hybrid microgrid, this paper analyzes the droop characteristics of the subgrid in AC/DC hybrid microgrid as well as the power balance relationship between the grid-connected mode and off-grid mode. To avoid the frequency action of the converters and improve the power quality, this paper proposes a droop control method for AC/DC hybrid microgrid based on unitized processing, designs the error action threshold, derives the mathematic relationship between the unitized error and the exchange power, and realizes the partial control of the interlinking converter. The simulation model of AC/DC hybrid microgrid built in PSCAD/EMTDC shows that, in both the grid-connected mode and the off-grid mode, the interlinking converter can quickly and accurately regulate the exchange power between DC microgrid and AC microgrid, and guarantee the stable operation of AC/DC hybrid microgrid, which verifies the feasibility of the control strategy.
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  Optimal Allocation of Power Supply in AC/DC Hybrid Stand-Alone Microgrid

  LIU Xingjie，DU Zhe，YAN Xiao

  Electric Power Construction. 2016, 37(10): 16. https://doi.org/10.3969/j.issn.1000－7229.2016.10.003

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  The optimal allocation of power supply in AC/DC hybrid microgrid can reduce the converter loss and system cost. According to the unique structure and energy flow pattern of AC/DC hybrid stand-alone microgrid, this paper proposes the specific energy management strategy with considering the power transmission efficiency. The optimal allocation model aimes at the optimal economy, and comprehensive consides environmental protection and power supply reliability. This paper adopts modified artificial bee colony algorithm to solve the model, which can obtain the optimal allocation result of distribution generation in AC/DC hybrid stand-alone microgrid. Finally, through the comparison and analysis of examples, it shows that AC/DC hybrid microgrid can save the operation costs of the system compared with AC microgrid or DC microgrid, and the application of improved energy management strategy can obtain the allocation scheme of power supply in microgrid with better economy.
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  Emergency Energy Management Strategy for Commercial Building Microgrid

  CUI Yi, LIU Nian, CHEN Qifang

  Electric Power Construction. 2016, 37(10): 16. https://doi.org/10.3969/j.issn.1000－7229.2016.10.004

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  When there is a power failure in distribution network, commercial building microgrid can be operated autonomously. In order to reduce the users loss caused by power outage and preserve the power supply of important loads during blackout, this paper presents a novel emergency energy management strategy for commercial building microgrid with photovoltaic-battery system, where planned and unplanned outages are both taken into account. When the outage is planned, an optimization model is established, aiming to reduce outage loss and preserve power, and weighting factors are introduced to weigh the importance of reducing loss and preserving power. Rolling optimization strategy is proposed to reduce the prediction errors on the result. When the outage is unplanned, a real-time emergency program is established, following the principle of giving priority to preserve the power supply of important loads. Comprehensive results obtained from comparison simulations show that the proposed strategy is efficacious in adjusting the input of controllable loads to reach the desired goals. Additionally, sensitivity analysis is carried out in case study section, and different weighting factors will flexibly adjust the importance of reducing outage loss and preserving power in the optimization goal.
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  Operation Control of DC Power Supply System in Green Data Center

  MENG Ming, LU Yuzhou, CHEN Shichao

  Electric Power Construction. 2016, 37(10): 33. https://doi.org/10.3969/j.issn.1000－7229.2016.10.005

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  To save energy and protect environment and reduce the apparatus room construction cost of data center, this paper introduces new energy into the power supply system and establishes the power supply system of green data center. This paper introduces the existing data center power supply modes, analyzes the deficiency of the traditional power supply mode, and designs DC power supply system of data center including PV generation, energy storage device, AC grid and load. On the basis of bus voltage stability control, the system operation is divided into eight operating modes to control the corresponding converter according to system operating mode and local information. This paper proposes the energy control strategy for the DC power supply system of green data center, which can ensure the reliability of power supply by coordinating and controlling the active power. Via Matlab/Simulink software, the simulation models of system are built respectively under grid-connection and grid-disconnection operations, the result of which verifies the feasibility of the proposes control strategy.
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  A Hierarchical Control Strategy of Autonomous DC Microgrid

  QIU Yaoyao,YANG Xiu,HE Hongli

  Electric Power Construction. 2016, 37(10): 41. https://doi.org/10.3969/j.issn.1000－7229.2016.10.006

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  The distributed control strategy with the supervision system has effectively solved the problem of voltage deviation brought by conventional droop control method. Considering the drawback of the previous distributed control strategy in voltage drop compensation and energy storage management, this paper proposes a novel hierarchical control strategy to achieve the reliable and optimal operation of stand-alone DC microgrid. The proposed control strategy includes two hierarchical layers. The primary control layer, which is the local control layer, uses bus voltage signal as an indicator of the power balance to change the operation modes of system. The secondary control layer is the system control layer based on communication links, which can achieve real-time bus voltage regulation by low-bandwidth communication technology, and adjust the drop control coefficient based on the battery state of charge (SOC) to balance the SOC between different batteries. This paper constructs the model for PV storage DC microgrid in MATLAB/simulink, whose simulation results verify that the primary control layer can ensure the reliable operation of the system without communication links, and after the addition of the second control layer with communication links, it can solve the problem of voltage deviation brought by conventional droop control method, and realize the balance of the SOC between different batteries.
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  An Improved Droop Control Method for Voltage and Frequency Restoration in Microgrid

  ZHANG Xinzhou, WANG Weiqing, WANG Haiyun

  Electric Power Construction. 2016, 37(10): 48. https://doi.org/10.3969/j.issn.1000－7229.2016.10.007

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  At present, the realization of the island microgrid control is generally based on droop control. The droop control can not only ensure the stabilities of voltage and frequency, and realize the reasonable load sharing of distributed generation. But for the high demand of power quality, there will normally be the recovery control of the voltage and frequency for the second time after droop control, which results in the increase of operating costs. In view of this problem, this paper proposes a method based on the ‘washing and filtering’ to restore the voltage and frequency after the analysis of the droop control principle. This method introduces a ‘washing and filtering’ controller before droop control, which can restore the voltage and frequency without increasing the secondary communication line. Through the simulation experiment in PSCAD/EMTDC software platform, the results show that this method can recover the voltage drop and the frequency deviation after the load change of microgrid.
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  Operation Characteristic Analysis for UHVDC Transmission in Separating Pole Connection Mode

  WANG Jing, HAN Minxiao, YAO Shujun, TIAN Chunzheng, SI Ruihua, TANG Xiaojun

  Electric Power Construction. 2016, 37(10): 54. https://doi.org/10.3969/j.issn.1000－7229.2016.10.008

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  The traditional two-terminal UHVDC transmission system has big impact on the receiving end because of its great capacity of power transmission. For this problem, this paper proposes a novel separating pole connection (SPC) mode, which can transmit power to two receiving power systems in different locations and voltage degrees. Firstly, this paper establishes the equivalent model of AC/DC system under SPC mode, presents the improved definition of separating pole connection short circuit ratio (SPCSCR), and analyzes the abilities of power transmission related with SPCSCRs. Based on the analysis on the layered structure of UHVDC transmission control system, this paper optimizes the structure configuration scheme of the SPC control. Based on the Henan Grid Planning in 2020, this paper verifies the rationality of the control strategy and analyzes its fault response through the simulation in PSCAD/EMTDC. Finally, this paper studies the impact of one pole fault on other poles power transmission, verifies the advantage of SPC, which can provide design reference for the grid planning of of UHVDC transmission.
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  Online Monitoring Technology of Thyristor Level of HVDC Converter Valve

  WANG Huafeng, WEI Xiaoguang,ZHENG Lin,HAO Changcheng,ZHANG Haifeng,LIN Zhiguang

  Electric Power Construction. 2016, 37(10): 61. https://doi.org/10.3969/j.issn.1000－7229.2016.10.009

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  Currently there are up to 29 HVDC transmission projects in operation or under construction in China, which are playing an important role in power grid. The converter valve is the core unit of HVDC transmission, whose performance largely influences the reliability of HVDC transmission project. This paper firstly analyzes the principles and shortages of existing monitoring technologies of HVDC converter valve. Then, this paper proposes a real-time online monitoring method for the parameters of thyristor-level damping circuit and DC grading circuit, and improves the self-check of thyristor trigger and monitoring unit (TTM). Finally, this paper verifies the effectiveness of the proposed monitoring method through simulation and experiment. As a result the annual preventive maintenance of converter valve is replaced by condition based maintenance, which can realize the maintenance free of converter valve in operation and improve the equipment's availability and reliability.
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  Coordination Optimization of Power Support Capability

  JIN Liming，ZHOU Ning，FENG Li，LU Zhiran，ZHAO Yuan

  Electric Power Construction. 2016, 37(10): 69. https://doi.org/10.3969/j.issn.1000－7229.2016.10.010

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  To alleviate the calculation complexity of power system reliability evaluation, this paper proposes a reliability evaluation model for power system based on network partition and coordination optimization of power support capability. This model determines the coordination solution sequence of subareas according to the generation margin, takes the tie line power between subareas as equivalent loads at the boundary nodes of subareas, and adopts the optimal load shedding model to optimize the load curtailment and power support capabilities of subareas successively according to the coordination solution sequence. Compared with the conventional partition equivalence technique of power system reliability evaluation, the proposed network partition and coordination model can realize the effective modeling of the power support capabilities among subareas, and enhance the reliability evaluation efficiency of power system while guaranteeing high accuracy, due to considering the generation margin and power flow constraints of subareas and adopting the optimization model to calculate the maximum equivalent load of subareas. Finally, this paper verifies the rapidity and effectiveness of the proposed model through IEEE-RTS96 test system.
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  VSC-HVDC Coordination and Stability Control Applied in Electromagnetic Loop Network

  LIN Cheng,MA Qinfeng, QU Yanxia, SHI Bonian,OUYANG Kefeng, KANG Peng, SUN Bin, ZHAO Weixin

  Electric Power Construction. 2016, 37(10): 80. https://doi.org/10.3969/j.issn.1000－7229.2016.10.011

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   This paper first analyzes the stability problems of electromagnetic loop network and the characteristics of VSC-HVDC system. Then, this paper puts forward the necessity of coordinated control of VSC-HVDC and stability control system when VSC-HVDC applied in electromagnetic loop network, and presents the coordinated control method of VSC-HVDC and stability control system, the calculation principle of measure quantity, as well as the alculation method of the coordinated control measures for transient stability. The numerical calculation of coordinated control measures based on equal area criterion considers the influences of action time delay and the reactance of the system, which can make the calculation results more accurate and the maximum use of the capacity of VSC power support for the power system in transient process. Finally, this paper adopts BPA simulation tool to establish the mechanical and electrical simulation model of VSC-HVDC applied in electromagnetic loop network. The simulation results show that the coordination control of VSC-HVDC and stability control systemwill reduce total number of the generator cutting compared to traditional stability control, and improve the voltage stability of AC system, which has a good engineering and practical value.
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  An Additional Frequency Pole Assignment Controller for VSC-HVDC

  ZHU Xianliang,ZHANG Yingmin,LI Xingyuan, CHU Zhengchao, GUO Lei,WANG Yuhong

  Electric Power Construction. 2016, 37(10): 86. https://doi.org/10.3969/j.issn.1000－7229.2016.10.012

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  In order to suppress the voltage source converter-high voltage direct current (VSC-HVDC) low frequency oscillation and improve its transmission capacity, this paper proposes a control strategy for pole assignment. We use the improved TLS-ESPRIT recognition algorithm to identify the open-loop transfer function of the system. According to the root locus diagram of the open-loop transfer function, we get the open-loop gain interval which makes it stable, and then get the closed-loop root locus poles under a better gain which are desired poles. And then we combine the desired poles with the configured observer poles to obtain a pole assignment controller. The application of the observer controller can not only reduce the work load but also have better robustness. To show the superior effect of the proposed controller, we adopted the classical root locus advance compensation method to design the controller and compared it with the proposed controller. The simulation results in PSCAD/EMTDC show that the effect of the controller designed by the classical root locus method is not obvious, while the proposed pole assignment controller can better restrain low frequency oscillation of VSC-HVDC under the different malfunctions, and therefore has better robustness.
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  Coordinated Control Robust Stability for VSC-HVDC Damping Controller Based on Effective Open-Loop Process Theorem

  LI Zhihan, ZHANG Yingmin, LI Xingyuan, DENG Qi

  Electric Power Construction. 2016, 37(10): 93. https://doi.org/10.3969/j.issn.1000－7229.2016.10.013

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   According to the phenomenon of low frequency oscillation in the AC-DC interconnected system with voltage source converter-high voltage direct current  (VSC-HVDC）, this paper converts multi-variable system loop matrix equation into many single variable system loop equation, and establishes the independent mathematical models of each circuit, based on multi-variable system effective open-loop process (EOP) theorem. For the potential uncoordinated problem of each loop controller in multi-input multi-output (MIMO) nonlinear system which contains VSC-HVDC, this paper proposes a coordinated control robust stability index of each supplementary damping controller based on small gain theorem and EOP theorem. Then, the power system stabilizer (PSS) supplementary damping controller and VSC-HVDC supplementary damping controller in cooperative operation was designed to restrain low frequency oscillation. Finally, AC/DC four machine two-area system with a VSC-HVDC in PSCAD /EMTDC has been established,  and  the validity of the proposed indicators and the feasibility of the designed controller have been verified through simulation.
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  An Improved Calculation Method of Distribution Network Harmonic Power Flow Considering Phase Sequence Characteristics of Harmonics

  SONG Mengqi, TAO Shun

  Electric Power Construction. 2016, 37(10): 100. https://doi.org/10.3969/j.issn.1000－7229.2016.10.014

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  As different order harmonics have different phase sequence characteristics, this paper proposes an improved calculation method of harmonic power flow for distribution network. Firstly, we analyze the phase sequence characteristics of harmonics. Next, we deduce the transformer models under different harmonic phase sequence with taking the impacts of transformers winding connection modes, connection set and neutral point grounding impedance on harmonic power flow into account; and discuss the calculation model of other electrical elements of distribution system with considering phase sequence. On this basis, the harmonic power flow with different phase sequences in MATLAB we analyzed. Finally, taking the IEEE 33-bus system and a practical distribution network including photovoltaic power station as examples, the power flow with or without considering phase sequence characteristics was  calculated  and  the results  were compared with the simulation results in PSCAD, which verify the feasibility and correctness of the proposed method.
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  Low Frequency Oscillation Type Discrimination Based on Initial Oscillation Waveform Data and Coherence Method

  WANG Lixin, CAI Guowei, YANG Deyou, SUN Zhenglong

  Electric Power Construction. 2016, 37(10): 108. https://doi.org/10.3969/j.issn.1000－7229.2016.10.015

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  According to the different excitations, the main low frequency oscillation of power system is forced oscillation and negative damping oscillation. The two kinds of oscillations are similar in form, but the control methods are quite different. We summarize the external characteristic and distinction of the two kinds of oscillations based on the deep analysis on the analytical expression of active power oscillation of power system, then put forward a oscillation type identification method on the basis of coherence method. Firstly, this method obtains two sets of initial data of oscillation which contains the noise through the wide area measurement system (WAMS) installed on the different generators, then calculates the magnitude squared coherence of the two sets of data based on coherence method. So we can identify the oscillation type by the comparison of the magnitude squared coherence. The simulation calculation and analysis of four-machine, two-area system verify the feasibility and effectiveness of the proposed identification methods.
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  Domestic Daily Load Curve Modeling Based on User Behavior

  LIN Shunfu, HUANG Nana,ZHAO Lunjia,TANG Bo, LI Dongdong

  Electric Power Construction. 2016, 37(10): 114. https://doi.org/10.3969/j.issn.1000－7229.2016.10.016

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  With the proportion of residential power consumption growing gradually, the residential loads have the increasing influence on the distribution network. The effective modeling of domestic daily load curve is critical for the development of demand side management and smart grid. This paper constructs the model of domestic daily load curve based on user behavior. We construct the electrical models of typical residential loads based on the tested data. And based on the statistic research data, we adopt Markov chain Monte Carlo (MCMC) method to construct the behavioral models of residential loads which introduces probability functions to represent the influence of resident household characteristics such as resident population and household appliances owned. Then, we adopt a bottom-up modeling method to construct the model of domestic daily load curve and the simulation platform with combining electrical model and behavioral model. The proposed model is universal and systematic, whose feasibility and accuracy are validated through the compared analysis between simulations and measurement.
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  Harmonic Transfer Network Analysis of Large-Scale Photovoltaic Power Plant Electricity Energy Collection System

  ZHU Yongqiang, HAO Jiacheng, TANG Qi, YANG Huina, LI Chunlai

  Electric Power Construction. 2016, 37(10): 122. https://doi.org/10.3969/j.issn.1000－7229.2016.10.017

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  In large-scale photovoltaic (PV) power plant, the output power of every PV grid-connected inverter system is collected by electricity energy collection system and then is put into electricity grid. Previous studies have demonstrated that the harmonic problem may occur when PV inverters run in parallel even if all the PV inverters individually satisfy the standards. Considering the electricity energy collection system, this paper builds the model of harmonic transfer network for typical topological structure of large-scale grid-connected PV power plant. Using node matrix method, this paper calculates the harmonic power flow of a given calculation example in MATLAB and gets the fundamental and harmonic voltage amplitudes of every node. Taking the node of the low voltage side of main transformer as the study object, this paper compares the calculation result with that of neglecting the structure of the electricity energy collection system, whose results show that the voltage amplification property obviously changes. Finally, this paper analyzes the influence of the parameters of LCL filter and cable in the electricity energy collection system on the voltage amplification property of the harmonic transfer network.
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  Multi-Objective Optimal Configuration of Distributed Generation Considering Uncertainties

  NIE Hongzhan, SHI Hao, YANG Jincheng, XIAN Yingnan

  Electric Power Construction. 2016, 37(10): 130. https://doi.org/10.3969/j.issn.1000－7229.2016.10.018

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   According to the influence caused by the uncertainty factors of grid-connected distribution energy resource (DER), this paper firstly establishes a probabilistic model for each uncertainty factors to coordinate the benefits in the investors of distributed generation (DG), grid company and social public; and establishes the multi-objective mathematical optimization model from three aspects of DG investment benefit index, transmission loss index and environmental index. Aiming at uncertain factors, this paper calculates the probabilistic flow based on the opportunity constrained programming to test the constraints condition of opportunity. Then, this paper proposes a multi-objective particle swarm optimization algorithm based on Monte Carlo simulation method (MPSO-MCS) to optimize the DC configuration. Finally, the example simulation results of an IEEE 33 node system show that the proposed model with considering the uncertainty factors of DG can optimize the configuration of DG more close to reality. According to the results after planning, the analysis results of system losses and voltage fluctuations under probabilistic method verify the effectiveness and rationality of the proposed model and method.
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  Economic Demand Response Modeling in PJM Electric Market Considering CBL Error Uncertainty

  WANG Jian, LIANG Huabin, DU Zhaobin

  Electric Power Construction. 2016, 37(10): 137. https://doi.org/10.3969/j.issn.1000－7229.2016.10.019

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  Though the economic demand response (EDR) in PJM (Pennsylvania-New Jersey-Maryland) electric market has implemented successfully, there are still some problems. According to the problems in recent years disclosed by ESPA Decision such as unbalanced interests, this paper propose a new EDR with the co-existence model of load shifting and load curtailment instead of the original EDR with only load curtailment mode, so that generators can also join the EDR in PJM electric market. Meanwhile, this paper considers the error uncertainty of customer baseline load (CBL) to accurately calculate the true response error of EDR when constructing the EDR model. The results of the case study show that taking CBL error into consideration can estimate the real cost of EDR error and the load shifting mode can coordinate the interests of generators, load service entities (LSE) and curtailment service providers (CSP) to a certain extent.
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  Solving Dynamic Economic Emission Dispatch Based on Period Coupling Characteristic

  WANG Xiaofei, HU Zhijian, ZHANG Menglin,HU Meiyu, WANG Xiang, DENG Aopan

  Electric Power Construction. 2016, 37(10): 144. https://doi.org/10.3969/j.issn.1000－7229.2016.10.020

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  This paper presents a new improved teaching-learning-based optimization algorithm (ITLBO) to solve the dynamic economic emission dispatch (DEED) problem based on the characteristics of period coupling. DEED is a bi-objective optimization problem, which minimizes the fuel cost and emission level simultaneously. In the proposed algorithm, the opposition-based learning (OBL) strategy is employed to improve the population diversity, the single interval teaching and learning process is used to enhance the local searching ability, and the single interval greedy selection strategy is adopted to explore a new domain in the whole searching space, aiming at balancing the local optimization and global optimization ability. Through the simulation analysis on the ten-unit 39-nodes system, the results show that the proposed strategy has a faster convergence rate and better convergence characteristic, and can obtain higher quality solutions.