Table of Content

05 October 2020, Volume 53 Issue 10

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Planning Methods for Transnationally Interconnected Power Systems under the Background of Clean Low-Carbon Development

ZHOU Yuanbing, JIANG Han, XIAO Jinyu, LIANG Caihao

2020, 53(10):  1-9.  DOI: 10.11930/j.issn.1004-9649.202006243

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Under the macro background of clean and low-carbon development for addressing global climate change, the current research on transnationally interconnected power systems has certain deficiencies in terms of geographic scope, time span, and multi-level coordination. We propose an orderly and coordinated framework for planning and research of transnationally interconnected power system, and introduces the key technical models such as scenario building, generation-grid collaborative planning, and environmental climate-economic-social benefit analysis. An overall work process is designed based on the “ work system” and “support system”. Taking the temperature limit of the Paris Agreement as the objective, a scenario analysis is carried out, including global power demand, power supply mix, energy flow and other issues, and the comprehensive benefits are evaluated. Finally, the planning research methods are summarized and relevant suggestions are proposed.

Modeling Methods of Static Hysteresis Characteristics of Electrical Steel Sheets under Stress

LI Yiling, LI Lin, LIU Ren

2020, 53(10):  10-18.  DOI: 10.11930/j.issn.1004-9649.202004045

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Accurate and rapid simulation of the hysteresis characteristics of magnetic materials under different stresses is of great significance to design electrical equipment cores that withstand mechanical stress. In this paper, the BROCKHAUS-MPG200 electrical steel test system was used to measure the hysteresis loops of silicon steel sheet samples under different stresses. and it is found that under the effect of stress, the hysteresis loops will produce local distortion, and the magnetic density is higher, the more serious of this distortion. Therefore, for the first time, this paper extends two commonly used simplified Preisach models to simulate the hysteresis characteristics of electrical steel sheets under stress, and finds that only one Priesach model is applicable. According to the characteristics of the model, the Everett function under different stress values can be identified only by using the measured limit hysteresis loop with distortion characteristics. this paper proposes the cubic interpolation method to extract the inverse Everett function with stress as a variable, and the static inverse Preisach model of electrical steel sheet under stress is established. Experimental and simulation results show that the model has high calculation accuracy and can be used for hysteresis characteristic simulation and hysteresis loss calculation of magnetic materials under stress in actual engineering.

Effect of Nb Addition on the Structure, Magnetic Properties and Annealing Embrittlement of A FeBCu Nanocrystalline Alloy

WU Licheng, LI Yanhui, ZHANG Wei

2020, 53(10):  19-25,33.  DOI: 10.11930/j.issn.1004-9649.202006191

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To improve annealing process and decrease annealing embrittlement of FeBCu nanocrystalline alloys, the effect of Nb content on the structure, thermal properties, crystallized structure, magnetic properties and brittleness of melt-spun Fe_86-xB₁₃Cu₁Nb_x (x = 0~6) alloy ribbons was investigated by using X-ray diffraction, transmission electron microscopy, differential scanning calorimeter, vibrating sample magnetometer, and bending test method. The results show that the increase of Nb content enhances the thermal stability of amorphous phase, and refines α-Fe grains, improves soft magnetic properties as well as reduces the annealing embrittlement of the annealed alloys. The addition effect on the structure and properties is significant when the Nb content exceeds 2 at.% and becomes moderate when Nb content ≥ 5 at.%. The decreased annealing embrittlement of the nanocrystalline alloys is mainly due to the reductions of both grain size and volume fraction of the α-Fe phase.

Modeling and Verification of A Novel Vector Hysteron Model

DENG Kai, LI Yongjian, CHENG Hao, GONG Xuehai, YANG Fuyao

2020, 53(10):  26-33.  DOI: 10.11930/j.issn.1004-9649.202006201

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A novel implementation of a hysteresis operator in the framework of Vector Hysteron Model (VHM) is presented to describe rotational magnetization. In order to simulate the effect of anisotropy on the magnetization process more effectively, this paper changes the method of using the equipotential surface to simulate the magnetization process in the VHM model, and discusses a new scheme. This model uses the bifurcation curve as the critical surface equation of the hysteron, and uses the method of the directed bifurcation curve to solve the hysteron's critical surface equation. To further discuss the simulation performance of the model under different excitations, this paper identifies the experimental data at different frequencies, and the Moving functions are used to describe the identified parameters. The comparison between simulation results and the experimental data has been given hereafter and it is shown that the new approach is acceptable and shows good effectiveness.

Study on Vibration Characteristics of Power Transformer Core and Oil Tank and the Correlation with Near Field Noise

FAN Chao, NIE Jingkai, XIAO Weimin, WANG Guangzhou, JI Shengchang, YANG Fuyao, LIU Yang, DU Pengyu

2020, 53(10):  34-41.  DOI: 10.11930/j.issn.1004-9649.202004089

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The noise of the transformer is mainly generated by the vibration of the oil tank, which is mainly generated by the vibration of the iron core, while the vibration of the iron core is mainly generated by the electromagnetic force. In order to study the correlation among ferromagnetic force, core vibration, oil tank vibration and near field noise. In this paper, the electromagnetic force of transformer in different direction under different voltage is simulated by using virtual work method, the vibration state of the core is analyzed by finite element method. And the vibration characteristics of the core and oil tank in different directions under different voltages and the near field noise characteristics of the transformer were tested by using acceleration sensors. At last the transmission process of core vibration is discussed. The results show that the magnitude, direction and frequency of ferromagnetic force are obviously correlated with the vibration of ferromagnetic core, the vibration of oil tank and the noise of transformer near field.

Effect of Mn on High Frequency Magnetic Properties and Microstructure of FeCuSiBNb Nanocrystalline Alloys

ZHANG Bojun, XIAO Huiyun, HE Aina, LI Jiawei, DONG Yaqiang

2020, 53(10):  42-49.  DOI: 10.11930/j.issn.1004-9649.202005105

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The effects of Mn element on the thermal stability, high frequency magnetic permeability, microstructure and magnetic domain of FeCuSiBNb alloys were studied utilizing DSC, XRD, TEM, MOKE, DC B-H loop tracer and impedance analyzer. With the addition of a small amount of Mn, the temperature interval between the first and second crystallization temperatures and the coercivity of the alloys remain almost constant, but the high frequency permeability and the interval of annealing temperature improve significantly. Compared with Mn-free alloys, the permeability of Mn-doped alloys at 10 kHz is increased by 36.5%, and the precipitation of Fe₃B phase is suppressed. This good properties in the Mn-doped alloys can be attributed to the fact that Mn doping reduces the mean grain size, and thus it improves the uniformity of the magnetic domains, which decreases the pinning field of the nanocrystalline alloys.

Measurement and Analysis of Hysteresis Loss of Nd-Fe-B Permanent Magnet under Superheated Loss of Magnetism

LI Yongjian, LI Haosen, GENG Hui, GONG Xuehai, YANG Fuyao

2020, 53(10):  50-57.  DOI: 10.11930/j.issn.1004-9649.202005057

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Rare earth permanent magnet materials, such as NdFeB, are widely used in permanent magnet motors because of their good magnetic properties, low price and good mechanical properties. The harmonic magnetic field in the motor will cause permanent magnet loss, which will lead to permanent magnet overheating loss of excitation and affect the stable operation of the motor. In this paper, through the design of permanent magnet comprehensive magnetic characteristics test device, quantitative application of AC magnetic field, it is found that under low frequency, saturation magnetization of NdFeB will appear obvious hysteresis phenomenon. In this paper, the hysteresis loss of NdFeB material under the condition of overheating loss of excitation is measured quantitatively and the magnetic characteristics are analyzed. It is found that the NdFeB with overheated loss of magnetism will produce obvious hysteresis loss.The test results show that the permanent magnet will lose its magnetism when it runs at high temperature for a long time, and the hysteresis loss of the permanent magnet will increase gradually, and even the hysteresis loss will be higher than the eddy current loss under certain conditions. This shows that the hysteresis loss of the permanent magnet will accelerate the failure of the permanent magnet, and in some cases is the main reason for the loss of excitation.

Zero-Error Frequency Regulation Control Method for Microgrids Based on Consensus Algorithm

CAI Guowei, BIAN Yudong, KONG Lingguo, SONG Jia, XU He

2020, 53(10):  59-65.  DOI: 10.11930/j.issn.1004-9649.202004155

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With the rapid development of energy technology, wind/photovoltaic-hydrogen production system will play a major role in the typical energy scenario. Based on the analysis of the power exchange characteristics of heterogeneous energy in wind/photovoltaic hydrogen production system, a homogenization analysis model of wind/photovoltaic-hydrogen production system was established from the perspective of power / energy supply and demand balance. Based on the analysis of the operation domain of the model, a unified analysis framework was formulated, and three dimensional analysis was conducted to study the boundary conditions of wind/photovoltaic-hydrogen production system. Furthermore, the output scatter diagram was plotted using the historical data to figure out the pattern of operation point as well as the index range of operation point such that the system operation domain can be analyzed reasonably.

Optimal Capacity Configuration of Solar-Hydrogen Independent Power-Supply System Considering Electricity-Heat Comprehensive Utilization

XIONG Yufeng, SI Yang, ZHENG Tianwen, CHEN Laijun, MEI Shengwei

2020, 53(10):  66-73.  DOI: 10.11930/j.issn.1004-9649.202006027

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Because of geographic limit and climate influence, the energy supply problem in remote regions of Qinghai-Tibetan Plateau has not been solved effectively. Considering of local characteristics of extended cold climate, abundant light resource and disperse load distribution, since hydrogen energy has advantages of non-pollution, carbon-free emission and high calorific value, this paper proposes a framework of solar-hydrogen independent power-supply system to realize heat-electricity comprehensive supply in extended cold areas. The heat-electricity united supply model of hydrogen storage system, containing electrolyzer, hydrogen tank and hydrogen fuel cell, is formed to make full of ability of heat-electricity joint stock and joint supply. On this basis, the capacity configuration model of solar-hydrogen independent power supply system is formulated and the optimization method is provided. By case study, the performance difference between solar-hydrogen independent power supply system and the current solar-battery independent system has been contrasted and analyzed. The feasibility of solar-hydrogen system independent power supply system has been validated, and the results are hopeful to provide new ideas and methods for distributed supply of clean power in remote regions of Qinghai-Tibetan Plateau.

Economic Analysis of the Application of Japan's Household Fuel Cell CHP System in China

SHEN Ruibao, DAI Xianzhong, JIANG Dongfang, HAN Xinyang, LU Qiang, JIN Xiaoling

2020, 53(10):  74-79.  DOI: 10.11930/j.issn.1004-9649.202006049

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Firstly, the technical principle of Japan household fuel cell CHP system (ENE-FARM) and its application are introduced. Secondly, in view of the complex characteristics of the factors that affect the economics of ENE-FARM, a general economic analysis model of ENE-FARM is established that takes into account equipment prices, annual household electricity consumption, electricity and gas prices and other factors. Thirdly, the break-even electricity price curve is used to analyze the economic differences of ENE-FARM applied in Japan and China, and a scenario analysis is made respectively for both 2020 and 2030. The results show that at present, ENE-FARM has the application economy in Japan, but has no conditions for large-scale promotion and application in China. It can be applied in remote areas such as islands and other disaster-prone areas. In 2030, with the gradual decrease of the equipment cost and perfection of residential electricity and gas price system, the application of the ENE-FARM system in domestic households will achieve a break-even.

Optimal Capacity Configuration and Day-Ahead Scheduling of Wind-Solar-Hydrogen Coupled Power Generation System

JIA Chengzhen, WANG Lingmei, MENG Enlong, YANG Derong, GUO Dongjie, LIU Yushan

2020, 53(10):  80-87.  DOI: 10.11930/j.issn.1004-9649.201909003

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In order to realize the optimal capacity allocation and day-ahead scheduling in wind-solar-hydrogen coupled generation system, the NSGA-II intelligent optimization algorithm is used to solve the multi-objective optimization problem of capacity allocation, and the optimal dispatching algorithm considering hydrogen transportation constraint is constructed on power generation side. Firstly, the equivalent mathematic model of each subsystem is established, and the economic indicator combining income and annual average cost of whole life cycle is put forward. Hydrogen production, fuel cell power and hydrogen storage capacity are obtained with the objective functions defined as system abandonment rate, power shortage rate and economy. Secondly, by taking the optimized capacity as the constraint condition of the day-ahead optimal coordinated control model, a single-objective optimization model is established to minimize the planning deviation and variation of pressure of hydrogen storage on the basis of the weighted coefficient method. Finally, the model is simulated and validated in Matlab. Hence the optimal capacity ratio and coordinated optimal control of the system is fulfilled.

Coordinated Dispatch Method for Integrated Microgrid Energy System Considering Interactive Hydrogen Conversion

YIN Chenxu, ZHU Liuzhu, XIANG Chao, YE Bin, ZHANG Li, LIU Hong

2020, 53(10):  88-95,148.  DOI: 10.11930/j.issn.1004-9649.201912028

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In order to take full account of interactive hydrogen energy conversion and utilization in the integrated energy microgrid, this paper proposes a coordinated dispatch method of the integrated energy microgrid. First, a typical architecture of the integrated energy microgrid considering hydrogen energy interaction is proposed. Second, the energy efficiency and economic model of key equipment is constructed with hydrogen energy as the core part. Then, the day-ahead dispatch model of the integrated energy microgrid is constructed and solved by taking advantage of the chaos enhanced fireworks optimization algorithm according to the related dispatch properties. Finally, through the comparison and analysis of actual case studies the effectiveness and applicability of the proposed model method are verified.

Energy Simulation and Optimal Scheduling of Integrated Energy System Considering Hybrid Energy Storage

LUO Yongwei, LI Chengren, ZHANG Ling, ZHANG Jianmin, WU Xinhong, LIAN Jinbu, FAN Jin

2020, 53(10):  96-103.  DOI: 10.11930/j.issn.1004-9649.202001087

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The complementary multi-energy based integrated energy system (IES) is an important way to improve regional energy efficiency and optimize energy resources allocation. An energy flow matrix model is established for the IES equipment with the minimal operating cost of the IES as the objective function, and a hybrid algorithm combining dynamic programming and the improved PSO is proposed. Under the same load and energy price settings, the horizontal analysis method is used to analyze the IES optimization under three working conditions, including without energy storage (condition 1), with sole thermal storage (condition 2), and with hybrid thermal-cold energy storage (condition 3). The results show that the operating costs of condition 3 and condition 2 are 14.65% and 5.92% lower than that of condition 1, respectively; The energy storage devices have significant effects on the optimal scheduling of IES, which can not only reduce the unnecessary use of energy-supply equipment, but also reduce the operating cost while ensuring a more stable system operation.

Combined Heat and Power System Dispatch Considering Heat Transfer Characteristics of Heat Exchangers

ZOU Liming, BIAN Xiaoyan, JIANG Jianjie, WU Henchao

2020, 53(10):  104-112.  DOI: 10.11930/j.issn.1004-9649.202002083

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The heat transfer characteristic of heat exchangers is one of the key factors affecting the optimal dispatch of combined heat and power systems. In order to optimize the dispatch of the combined heat and power systems, a three-stage heat transfer model of the extraction steam is established based on the heat transfer principle to describe the heat transfer process of the heat exchanger, and the iteration method is used to calculate the extraction steam under a certain heat load. And then, a joint dispatch model of cogeneration power, thermal power and wind power is proposed with consideration of the heat transfer characteristics of the heat exchangers. Finally, with the minimum coal consumption as the optimization goal, an analysis is made of the influence of the heat exchanger’s heat transfer characteristics on the steam extraction heat transfer process and the combined heat and power system dispatch results. The case study shows that increasing the heat transfer area of the heat exchanger and reducing the water temperature at the outlet of the heat exchanger can improve the wind power consumption capacity to different degrees, and reduce the operating cost. The research results of this paper can provide heat transfer parameters for optimizing the dispatch scheme of the combined heat and power systems.

Coordinated Optimization Operation Strategy for Multi-Energy Center with Power-to-Gas Devices

ZHANG Lei, QIN Guangyu, LIU Yaling

2020, 53(10):  113-122.  DOI: 10.11930/j.issn.1004-9649.202002013

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Application of power-to-gas (P2G) technology enables the two-way closed-loop energy flow between the power network and the natural gas network, which can promote the accommodation of intermittent clean energy. The power-to-gas process is divided in this paper into two stages: power-to-hydrogen and hydrogen-to-natural gas, and added with hydrogen storage devices to better coordinate the energy flow between power energy, hydrogen energy and natural gas energy. Aiming at the lowest operating cost and maximum wind power accommodation, a coordinated optimization operation model is constructed for multi-energy center with power-to-gas devices considering the operational constraints of power-to-gas, natural gas pipe network and various energy equipment. The model linearizes the nonlinear constraints of the natural gas network power flow, and converts the bi-objective optimization problem into single-objective optimization by adding the weight coefficient. Finally, in order to verify the feasibility and effectiveness of the established model, a four-node multi-energy network system was selected for simulation analysis. The branch definition method of YALMIP toolbox was used to solve the model, and the operating cost and wind power accommodation rate of the system were analyzed under different scenarios with different weight coefficients. The results demonstrate that the power-to-gas is feasible in operation of the multi-energy center, and the higher the utilization demand of the intermediate hydrogen gas, the greater the wind power accommodation rate is.

Operation Optimization and Reliability Evaluation of Integrated Energy System Based on Improved Timing Constraint Petri Net

HU Liexiang, WANG Lei, DONG Mingfeng, LI Hongzhong, SUN Ke, HU Zhesheng

2020, 53(10):  123-132,139.  DOI: 10.11930/j.issn.1004-9649.202003183

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The integrated energy system (IES) contains many types of equipment and load, and the coupling modes between the equipment are varied. In the construction process of actual integrated park, it is very important to evaluate the economy and reliability of different energy supply modes. Firstly, this paper establishes an operation optimization model of the IES system according to the basic modeling principle of the time constraint Petri net (TCPN), and by constructing the timing model of the cool and heat energy supply system, the general model coupling equipment and the energy storage devices. And then, the two-state model of the components in the system is analyzed to establish the system state space model. The corresponding energy supply reliability indexes are calculated by random sampling of the system state. Finally, the reliability and economy of multi-energy system under different operation modes are evaluated through case study of an actual integrated park with multi-energy storage, such as heat storage, electricity storage and gas storage.

Observability Analysis on State Estimation of Integrated Electricity-Gas System

YANG Xiaonan, LANG Yansheng, YAO Yuan, CHEN Yanbo, ZHU Chengzhi

2020, 53(10):  133-139.  DOI: 10.11930/j.issn.1004-9649.202006094

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State estimation plays a vital role in the operation monitoring and optimal dispatching of integrated electricity-gas system(IEGS). Before state estimation, observability analysis should be carried out for the system according to the existing measurement configuration to ensure the normal operation of state estimation. Because of the significant difference between the time constant of the electricity system and that of gas system, the differential-algebraic model is generally used to describe the coupling system of the two systems. Firstly, the finite difference method is used to differentiate the partial differential equation for describing the dynamic characteristics of natural gas. On this basis, the observability analysis is carried out for the IEGS, and the judgment basis and analytical steps are obtained for the observability analysis of the IEGS. Finally, the effectiveness of the proposed method is verified by a case study.

The Collaborative Optimization Model of Park Energy Supply and Use Considering the Change of Supply - Demand Regulation Cost

LUAN Fengkui, TANG Yanmei, JIN Lu, LI Kecheng, LIU Zhiyuan

2020, 53(10):  140-148.  DOI: 10.11930/j.issn.1004-9649.202004046

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For an integrated energy system (IES) of park with flexible load, the production of cold, heat, electricity, and steam can be changed by adjusting energy conversion equipment, and the load can also be changed by demand-side management. All energy conversion equipment operation and demand control measures require corresponding costs. It's necessary for integrated optimization of equipment side and demand side of energy products (such as cold, heat, electricity, and steam) to reduce cost of IES. In this paper, mathematical models for the various types of energy conversion and demand response costs are established, with the goal of minimizing the overall cost of energy supply, to comprehensively optimize the energy conversion system design and demand-side management in IES. The results show that compared with simply adjusting the output of energy conversion system, the coordinated regulation of energy production and demand side of the integrated energy system has the potential to further reduce the cost of integrated energy supply and utilization system.

Economic Operation Optimization for New Energy Microgrid Based on Deterministic Method

SUN Yingshuang, LUO Cong, GE Leyi

2020, 53(10):  149-155.  DOI: 10.11930/j.issn.1004-9649.202004219

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In view of the typical application scenarios of microgrid, the mathematician rules of prediction errors for photovoltaic power, wind power and load are analyzed. With consideration of environmental protection and economic factors, an economic operation optimization model of microgrid based on deterministic method is constructed, which simplifies the difficulty for multi-objective problem solution. In a specific example, the influences of different confidence levels, different prediction errors and different environmental penalty factors on the microgrid operation are analyzed. The result shows that improving the prediction accuracy of photovoltaic output, wind power output and load can reduce the operation cost of microgrid. Moreover, the deterministic method has advantages of fast convergence speed and short iteration time for solving the optimization model of microgrid.

Performance Degradation Based Lifetime Evaluation of Power Electronic Devices

PAN Guangze, ZHANG Zheng, LUO Qin, LI Xiaobing, MENG Linghui

2020, 53(10):  156-162.  DOI: 10.11930/j.issn.1004-9649.201907027

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Current lifetime evaluation methods are often ineffective for power electronic devices which have high reliability, long life, and multi-fault mode competition. Accordingly, a lifetime evaluation method based on performance degradation data is proposed. Such data is used to construct performance degradation and lifetime distribution models. Then, the model parameter estimation, model goodness-of-fit checking, and model optimization methods are derived. By considering the trends in the degradation of multiple performance parameters, a competitive failure model is constructed to achieve a fast evaluation for the lifetime of power electronic devices with high reliability, long life, and multi-fault mode competition. As an example, lifetime evaluation is carried out for an insulated gate bipolar transistor. The difference between the evaluation results and measured test results is small, which verifies that the proposed method is quite accurate and effective.

High Reactor Configuration and Power Frequency Resonance Analysis for The Cuting-Off of 220 kV Single-Circuit Long Line

CAO Bin, MIAO Lifang, YUAN Shuai

2020, 53(10):  163-171.  DOI: 10.11930/j.issn.1004-9649.201902021

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In order to avoid overvoltage in the power grid, shunt reactor is usually installed at both ends of long lines. As the power grid construction is expanding, long lines are often cut off and new substations are connected into the grid in order to improve the transmission capacity of grid. In the process, resonant accidents caused by improper configuration of shunt reactor are frequent. Based on PSCAD software, the precise electromagnetic transient model of renewable energy transmission project through 220 kV single-circuit long line is established in this paper. The dynamic characteristics of power frequency resonance and the parameter configuration of the shunt reactor and a small neutral reactor are analyzed. The influence trend of line-to-ground capacitance, line compensation degree and neutral reactor with power frequency resonance are analyzed quantitatively. Finally, the resonance problem is settled successfully with the proposed method, which can provide technical reference and practical experience for the design and operation of power grid.

“Cost-Accuracy” Hedging Based Load Forecasting Technique on Two-Stage Electricity Market

CUN Xin, QIAN Zhongwen, SUN Yixin, WANG Ke, WANG Yue, HUANG Zhiheng, WANG Zhimin, SHI Huicheng, LAI Lai li

2020, 53(10):  172-179.  DOI: 10.11930/j.issn.1004-9649.201809003

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Electricity plays an irreplaceable role in the national economy as a fundamental industry. Electricity contributes to the stable operation and scheduling of the power grid, promotes the efficient consumption of energy and avoids waste of resources. In most of electricity markets, the Load Serving Entities (LSEs) would submit the load scheduling by adopting model of load forecasting, which can be provided as a basis for trading in day ahead market. At present, most of load forecasting model focus on predicting accuracy instead of the fluctuation of market prices and LSEs’ benefits. This paper proposes a load forecasting strategy which balances accuracy and economic efficiency for two-stage electricity markets and establishes a “Cost-Accuracy” hedging based load forecasting technique (CAHFT). This technique is based on the traditional load forecasting technique, the term cost is introduced into the objective function, the improved backpropagation is used as the neural network for training. Case studies uses load data in New York area, and the verification results show that CAHFT has obvious effects on quantifying the benefits of the LSEs and contributing to the comprehensive improvement of its economic efficiency and accuracy.

Optimization of Generator Arrangement for Jin-Zhong HVDC

XIE Huifan, MEI Yong, ZHOU Jian, XU Guanghu, HUANG Lei, LI Ming, ZHAO Xiaobin, YANG Jian

2020, 53(10):  180-186.  DOI: 10.11930/j.issn.1004-9649.201805153

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The paper proposes an optimization method which gives the minimum on-service generator number during the low-water and low-load period on the basis that the power system is safe and stable. The optimization considers three aspects, effective short circuit ratio, stability under island mode and low-order resonance. It is found that the introduction of active DC blocking during isolated operation mode can help effectively eliminate the risk of shortage of short-circuit current, power oscillations and low-order resonance. Operational practice suggests that the minimum on-service generator number of Liyuan and Ahai power plants can be reduced to two respectively when the proposed approach is applied. By reducing the on-service generator number, the risk of having generators operate without load during the low-water and low-load period is alleviated substantially, thus ensuring the safety of equipment of power plants during island mode.

Zero-Error Frequency Regulation Control Method for Microgrids Based on Consensus Algorithm

WANG Yue, YANG Guohua, ZHUANG Jiayi, PAN Huan, ZOU Yuqi, HAN Shijun

2020, 53(10):  187-191.  DOI: 10.11930/j.issn.1004-9649.201907162

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For islanded microgrids, the microgrid system frequency with traditional droop control often deviates from the rated frequency due to the variation of output power. Therefore, a self-adjusting droop coefficient control strategy for microgrids is proposed. Through the consistency algorithm, the micro-power source in the micro-grid obtains the self-adjusting amount of the droop coefficient to achieve no static difference in the frequency of the micro-grid, while ensuring that the active power shares the load according to the rated capacity. A microgrid simulation model is built in PSCAD, and the simulation result verifies the effectiveness of the control strategy through comparison with that of traditional droop control.

Application Study of Distributed Grounding Line Selection Method Based on GOOSE Communication

CHEN Hongshan, YU Jiang, JIANG Miao, SHI Yong, HOU Wei

2020, 53(10):  192-199.  DOI: 10.11930/j.issn.1004-9649.201905038

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A GOOSE communication-based distributed grounding line selection method is introduced and implemented in the relay protection device. When a single-phase grounding fault happens in the small current grounding system, the fault current is quite small due to the switching of arc-extinguish coil, which makes it difficult to recognize the fault line using the conventional steady-state discrimination method. The wavelets decomposition algorithm is utilized to discriminate the transient component of current and to recognize the grounding line rapidly and accurately. The GOOSE communication of the station control layer is used to share information among several devices, and the wavelets algorithm is used to discriminate the fault line locally. The algorithm is proved feasible through MATLAB simulation, and the microprocessor protection device embedded in the algorithm is validated in the RTDS test.

A Practical Approach for Optimal Power Distribution Among the West-to-East Power Transmission Channels with Minimized Losses

CHENG Gaihong, ZHU Qingchun, YAN Jing

2020, 53(10):  200-205.  DOI: 10.11930/j.issn.1004-9649.201911093

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In order to reduce the power losses in power transmission from West to East, an optimal power distribution strategy with minimized losses is studied for the West-to-East power transmission channels based on both theoretical analysis and simulation calculations. The optimal power percentage of each DC transmission channel is determined with the principle of equal loss incremental rate. Based on the optimal power distribution among the DC transmission channels, the power system simulation tool is adopted to search for the reasonable power distribution between AC and the whole DC transmission channels. By introducing the step by step search strategy, the multivariable optimization problem involving power distribution among multiple transmission channels is converted to single variable optimization problem. Based on the line search strategy including advance and retreat algorithm and golden section algorithm, the optimal power distribution among transmission channels is thus determined through a small number of iterations. The proposed approach has been applied to West-to-East power transmission channels of CSG system, and the results demonstrate that the proposed approach is practical and easy to use, which can provide reference for dispatching and economic operation of power system.

Operation Characteristics and Security Control Measures of UHV Loop Network with Multi-Hierarchical DC Infeed after Breaking

BAI Shuaitao, CHEN Dezhi, MA Shiying, DONG Qing, TANG Wei, JI Ping, YANG Cheng, JIANG Xikai

2020, 53(10):  206-214.  DOI: 10.11930/j.issn.1004-9649.201909024

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The operation of a provincial UHV AC loop network provides conditions for hierarchical access and full power accommodation of multiple UHV DC systems, and also increases the coupling strength between UHV AC and UHV DC, and between 1000 kV/500 kV AC power grids at the receiving end. To ensure the reliable operation of UHV AC/DC power grids after line fault occurs, simulation is used to analyze the voltage stability characteristics of the coupled AC and DC systems after breaking of the 1000 kV UHV loop network, and the thermal stability characteristics of the power system when large power transfers to the 500 kV power grid after breaking, and the causes for voltage stability and thermo-stability problems are studied. In order to reduce the amount of security control measures, a unified multi-resource co-control optimization model is established for controlling the two operational problems, with consideration of the sensitivity and priority of multiple control methods such as DC modulation and load shedding. And a control-cost-based heuristic optimization method of constant-step gradient descent is proposed to obtain the co-control measures. It is verified through simulation of an actual power grid that the proposed controlling method can effectively reduce the amount of prevention and control measures.

Coordinative Two-Stage Superheated Steam Temperature Linkage Control Based on Multivariable Generalized Predictive Control Algorithm

TONG Sheng, LIU Le, WANG Pengfei

2020, 53(10):  215-223.  DOI: 10.11930/j.issn.1004-9649.201909059

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In addition to their own characteristics such as long duration of time delay and large inertia, the controlled objects of superheated steam temperature in large thermal power generating units are affected by a considerable number of factors and model variations under different loading conditions. Especially with complicate coal quality or under volatile environment, the effect of superheated steam temperature control turns out to be very limited, which are based on traditional PID control and single variable generalized predictive control. In this paper, the models of superheated steam temperature system under three typical working conditions are established by virtue of recursive least square method, and then an optimization strategy of two-stage superheated steam temperature linkage control based on multivariable generalized predictive control (MGPC) is constructed. Meanwhile, the strategy is applied to the 330 MW subcritical units in a power plant. The practice results show that the optimal control strategy is effective to control the outlet steam temperature of superheater whenever the system is operated under stable loads or complicated variable loads.

Design of the System for Dry and Wet Sludge Coupling Combustion for the Coal-Fired Boiler

FANG Zhaojun, FENG Bingquan, PANG Yi, HU Bo, ZHAO Wei

2020, 53(10):  224-230.  DOI: 10.11930/j.issn.1004-9649.201912174

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It is a more preferable choice to process the household garbage with high-efficiency pollutant treatment facilities of coal-fired power generating units. Regarding a coal-fired power generating unit capable of firing both wet and dry sewage sludge (with the water contents of about 80% and 20% respectively) in the transformation project, this paper conducts the study on the odor and the sewage generated during the sludge drying process from the coupling combustion in the coal-fired boiler. Also it proposes the optimization design for their treatment system. The odor produced in the stages of receiving, drying and transportation of sludge is collected by the overall micro-negative pressure control of the workshop and the local negative-pressure pumping of the drying device, then through the secondary air bellows system fed into the boiler, and eventually eliminated completely after high temperature combustion. The condensed sewage is mixed into the domestic sewage with low organic pollutant concentration, then treated in the subsequent biochemical treatment process and finally flows into the intermediate water pool for the existing industrial wastewater and hence recycled without any external discharge. With these improvements, the potential secondary pollution that may occur in the process of sludge coupling disposal has been avoided. The design can provide references for the transformation project of other similar coal-fired boilers coupling with sludge disposal.