Table of Content

05 March 2020, Volume 53 Issue 3

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Short-Term Power Prediction for Wind Farm and Solar Plant Clusters Based on Machine Learning Method

CUI Yang, CHEN Zhenghong, XU Peihua

2020, 53(3):  1-7.  DOI: 10.11930/j.issn.1004-9649.201907013

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Regional wind power and PV(photovoltaic) power forecast is an effective way to improve the robustness of power grid, however, the traditional single-station power accumulation method is poor in accuracy and operation efficiency, because the construction time of each station is different and the accuracy of single-station is various. Therefore, this paper proposes a method for short-term regional wind and PV power prediction based on feature clustering. Firstly, the machine learning-based Bisecting K-Means(BKM) clustering algorithm is used to reasonably divide the wind farms and PV stations in the region into clusters; Secondly, based on the correlation between of the historical power data of each power station and the total historical power data in the region, a representative power station is selected for each region; Thirdly, after optimizing and correcting the NWP(numerical weather prediction) model of each representative power station, a short-term power prediction framework model is established using BP neural network based on the cluster division of wind farms and PV power plants. The result shows that the proposed method is higher than or close to the traditional single-station power accumulation method in short-term prediction accuracy, but it can significantly improve the modeling efficiency while ensuring the prediction accuracy.

An Optimal Weekly Operation Strategy for Power Systems with Renewable Energy

ZHAO Shuqiang, CHEN Jiajun, LI Zhiwei, DONG Ling

2020, 53(3):  8-17,51.  DOI: 10.11930/j.issn.1004-9649.201910035

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In order to coordinate the completion of monthly contract electricity quantity, an optimal weekly operation model for multi-source hybrid power system including wind, photovoltaic, cascade hydropower and thermal power is established and analyzed in this paper. A rolling coordination and dispatching strategy, including monthly contract energy decomposition, optimal weekly dispatching and day-ahead dispatching is proposed. Water inflows and rolling modes that affect optimal weekly scheduling are analyzed. Case studies show that the proposed optimal weekly scheduling model can properly allocate water resources of cascade hydropower stations, improve overall operation efficiency of the stations and coordinate monthly electricity completion when the inflows are large during the water storage period.

Research on LVRT Control Strategy of Photovoltaic System Based on Hybrid Control Algorithm

YANG Chunbo, WANG Jingjing, KANG Peng, ZENG Linfeng, ZHENG Feng

2020, 53(3):  18-27,58.  DOI: 10.11930/j.issn.1004-9649.201911060

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A low voltage ride-through (LVRT) control strategy of photovoltaic (PV) system based on a hybrid control algorithm is proposed to solve the problems of DC-link overvoltage and AC side overcurrent of grid-connected inverter when the power grid voltage drops. Firstly, based on model current prediction control, the inverter grid-connected current can quickly follow the reference instruction and the symmetrical current can be always obtained to solve AC side overcurrent problem in the case of symmetric and asymmetric faults. Secondly, based on the voltage sag of the point of common coupling (PCC) and the adaptive non maximum power point tracking (Non-MPPT) algorithm to adjust Boost converter's duty ratio, the output power of PV array can be reduced, so that DC-link overvoltage can be inhibited in the failure process which is caused by the power imbalance between AC and DC side of the grid-connected inverter. By introducing DC-link voltage feedback, the second harmonic component of DC-link voltage can be removed in the asymmetric fault condition. Finally, the correctness and effectiveness of algorithm proposed are verified by Matlab/Simulink simulation system.

Subsynchronous Oscillation Features and Control Measures for Wind Power Influx Area near HVDC

WANG Shengli, XU Gang

2020, 53(3):  28-34,65.  DOI: 10.11930/j.issn.1004-9649.201911070

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The power electronic devices which are widely used in wind power influx area, especially near the HVDC area, can easily produce a large number of subsynchronous harmonic. According to the subsynchronous oscillation problem that emerged in the wind power integration areas near the ±800 kV HVDC in Hami, Xinjiang, the oscillation features and influence factors are analyzed to propose three measures to monitor, control and prevent subsynchronous oscillation. Experimental results show that the subsynchronous oscillation can be accurately detected by using the monitoring system and effectively prevented by taking the control measures, ensuring stable operation of the power grid.

Construction of Mobile Patrol Management and Control System for Power Transmission Channel

ZHANG Lei, JIANG Zhibo, WANG Haitao, TAO Hantao, WANG Zhao, WU Dawei, CHEN Yue

2020, 53(3):  35-42.  DOI: 10.11930/j.issn.1004-9649.201905094

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The geographical environments of transmission lines are mostly complex, and the maintenance of transmission lines is difficult. In order to make effective use of the patrol resources, and unify the working mode and standardize the management mode, a safe and reliable patrol management and control scheme for transmission channels is studied, and a mobile patrol management and control system platform for transmission channel is developed in this paper, based on an analysis of the daily inspection requirements and contents of power transmission channels. The effective integration and real-time display of patrol data are realized using mobile terminal and internet technology. The transmission channel patrol management and control services are provided for operation and maintenance department of power system by relying on the vast patrol resources. At present, the developed system platform is now deployed in the Lightning Monitoring and Early Warning Center of State Grid in Wuhan NARI, and has successfully provided patrol control services for three major UHV DC transmission lines. A large amount of effective inspection data has been accumulated, which can provide reliable technical support for patrol and management of transmission channels.

Suppressing Effect of Synchronous Condenser on Transient Overvoltage of UHVDC System under Hierarchical Connection Mode

QIAO Li, WANG Hang, XIE Jian, GUO Chunyi

2020, 53(3):  43-51.  DOI: 10.11930/j.issn.1004-9649.201910021

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At present, hierarchical connection mode has been adopted in UHVDC projects, and with the increasing proportion of new energy generation, the power grid at the sending end is facing the problem of transient overvoltage (TOV), which can be restrained by installing synchronous condensers, so it is necessary to study the suppressing effect of synchronous condensers on the TOV of UHVDC system under hierarchical connection mode. A model is established for the UHVDC system under hierarchical connection mode with synchronous condensers, and the suppression mechanism of synchronous condensers for TOV is analyzed theoretically. The effect of different number of synchronous condensers on TOV is studied under four different working conditions, including power-down operation, bipolar blocking fault, unipolar blocking fault and simultaneous commutation failure of both high-end and low-end inverters. Finally, the TOV-based short circuit ratio increment (SCRI) is proposed, and the suppressing effect of synchronous condenser on TOV is quantitatively evaluated. The results show that the proposed index can be used for quantitative evaluation of the suppressing effect of synchronous condensers on TOV. When the short circuit ratio of AC system on the rectifier side of UHVDC system under hierarchical connection mode varies from 3 to 8, the TOV-based SCRI at the rectifier side AC system is between 0.106 and 0.396 after one synchronous condenser is put into operation, and between 0.251 and 0.788 after two synchronous condensers are put into operation. Therefore, the implementation of synchronous condensers can effectively enhance the short circuit ratio of AC system and effectively restrain the TOV at the sending side.

Commutation Algorithm for Three-Phase Unbalanced Load Regulation in Distribution Network

LI Yongxia, GONG Yulei, GUO Xiuxiao, ZHAO Yanyan

2020, 53(3):  52-58.  DOI: 10.11930/j.issn.1004-9649.201901104

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Automatic phase commutation system is widely used to deal with the load imbalance problem in low voltage distribution network. It consists of an intelligent commutation terminal and a number of phase commutation switches. In the commutation switch, the compound switch of paralleled magnetic latching relay and bidirectional thyristor is selected as commutation switch actuator, in which the thyristor is cut off by zero switching at the moment of commutation, and the magnetic latching relay is switched on without large current. The hardware devices are generally used to detect the zero crossing point on the line voltage. As high frequency harmonic waves exist on the line voltage, the zero crossing point is hard to be detected accurately, and dedicated phase trigging can not be implemented using this method. Therefore, the software method is used to calculate the line voltage phase, and a reliable commutation algorithm is adopted to realize the regulation of three-phase imbalance, which effectively prevents the impact impulse to load and power grid, consequently improving the reliability in triggering thyristor. Experimental results show that the proposed algorithm is feasible in solving three-phase unbalanced loads and improving power supply quality.

Hybrid Dynamic Simulation Method of Power System Based on Impulse Load Injection

ZHANG Yanjun, LIU Jiaqi, GAO Kai, ZHANG Jian, ZHOU Zaiyan, JIANG He

2020, 53(3):  59-65.  DOI: 10.11930/j.issn.1004-9649.201904095

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Hybrid dynamic simulation is an important tool for power system simulation and validation. In this paper, a hybrid dynamic simulation method of power system is proposed based on impulse load injection, which directly injects the measured data containing constant power and impulse power into the simulation subsystem to achieve decoupling between subsystems. This method avoids the simulation error that may be caused by the dynamic equivalent of the external system. Based on the load model provided by the commercial software PSASP and the inherent impulse disturbance module, the proposed method is simple and easy to implement, and avoids the use of UPI/UD to write the interface program, thus having high practicality. A case study is conducted on an IEEE 10 machine 39-bus test system and a provincial power grid, which has verified the effectiveness of this method.

Evaluation and Optimization of Power Network Planning Scheme Based on Total-Cost Price

HE Kai, WANG Jianxiao, WANG Jiawei, LI Qiang, WANG Yao, XING Yahong, ZHONG Haiwang

2020, 53(3):  66-75.  DOI: 10.11930/j.issn.1004-9649.201908030

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In view of the actual challenges and urgent needs faced by power grid enterprises, a total-cost price model is proposed with consideration construction cost and operation maintenance cost, in which the power flow tracing method and stamp method is used respectively to allocate the power grid construction cost and operation maintenance cost based on the conventional nodal pricing mechanism. Furthermore, an evaluation process for power grid planning scheme is proposed based on the total-cost price model, which takes both security and economy into account, and the IEEE 14 and IEEE 33 bus systems are used to validate the effectiveness of the proposed evaluation method. The numerical simulation results show that the proposed total-cost price model can not only evaluate the power line planning schemes of different voltage classes, but also optimize the investment portfolio of different distribution networks. The research results can provide a quantitative analysis method and decision-making support tool for power grid enterprises to plan power grid investment in the context of new electric power reform.

Analysis and Prediction of Micro-meteorological Parameters for Power Transmission Lines in Micro-terrain Environment

LI Longji, XI Xiaoguang, LI Zhijian, WANG Xiaoguang, WEN Qingfeng, LI Qiran, ZHOU Kai, LIU Yong, YAO Juntao

2020, 53(3):  76-83.  DOI: 10.11930/j.issn.1004-9649.201907161

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In order to investigate the weather conditions of the transmission lines in micro-terrain areas, a research is carried out on the formation mechanism of micro meteorology in mountainous micro-terrain environment by taking three transmission lines in North China Grid, which are located in typical micro-terrain areas and had tower failure accidents in history, as examples, and a regression prediction model is established between micro-terrain meteorological factors and macro atmosphere parameters with the multiple regression analysis method based on the micro-climate theory. The research results show that the method can quantitatively reveal the relationship between micro-meteorological parameters, and can be used to analyze and predict the micro-meteorological parameters for the transmission lines in micro-terrain environment. The research in this paper can provide a basis for real-time evaluation of electrical reliability of transmission lines and establishment of early warning system.

Research on Hybrid Electric Field Distribution of UHV AC/DC Parallel Transmission Lines

FANG Shubo, FENG Zhihui, ZHANG Guangzhou, YAO Degui, LI Mu

2020, 53(3):  84-90.  DOI: 10.11930/j.issn.1004-9649.201808019

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In order to reduce the electrostatic induction effect of hybrid electric field generated by the UHV AC/DC parallel lines on residential houses and metal supports near the transmission corridor, this paper put up shielding wires paralleled to the AC/DC lines on the platform of residential buildings in the parallel to the AC/DC lines were established, and measured Distributions of the power frequency electric field and DC ionized field in parallel line direction were measured respectively, and the impacts of wires' height and number on the shielding effect on the hybrid electric field were also analyzed. And then built grape trellis metal support models for grape growing parallel to the AC/DC lines were set up, and the induced voltage distributions with different grid structures were measured. The results show that the shielding wires can effectively improve the spatial mixed electric ionized field under transmission lines can be effectively reduced by the shielding wires, and that has exist the best shielding structure of the wires also exists. The induced voltage of the metal support was greatly influenced by the support, and the maximum voltage value had no tingling sensation to the human body.

Research on Comprehensive Evaluation Method of High Reliability Wiring Mode for Medium Voltage Distribution Network

HAN Jun, XIE Zhenjian, GENG Lu, QIN Hua, CHEN Xi, WANG Na

2020, 53(3):  91-100.  DOI: 10.11930/j.issn.1004-9649.201809127

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In order to solve the problem that there are too many evaluation indicators and no unified standards for planning and design of medium-voltage distribution network wiring mode in high-reliability area, this paper studies the comprehensive evaluation method of high-reliability wiring mode for medium-voltage distribution network. Firstly, a comprehensive evaluation indicator system of high-reliability wiring mode is constructed from four aspects:reliability, economy, technology and adaptability. Secondly, the DEATEL-ANP-anti-entropy weight method and improved gray correlation method are used to determine the weights of each evaluation indicator. And then, the polynomial difference method is used to analyze the indicator rating function of high-reliability wiring mode. Finally, based on a high-reliability renovation project in a type A area in Jiangsu, a comprehensive evaluation and comparative study is carried out on the single-ring network wiring, double-ring network wiring, petal type wiring and three-way for same supply wiring mode with flexible DC loop. The results show that the three-way for same supply wiring mode with flexible DC loop has higher reliability and applicability with high comprehensive ratings, which conforms to the engineering reality, and proves the feasibility and effectiveness of the proposed comprehensive evaluation method.

Reliability Analysis of Repairable Stability Control System Based on Hierarchical Markov

QIE Zhaohui, LI Wei, CUI Xiaodan, LIU Fusuo

2020, 53(3):  101-109.  DOI: 10.11930/j.issn.1004-9649.201805154

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The reliability modeling analysis of the stability control system is still vacant. It is therefore of great significance to establish a reliability analysis model of the stability control system so as to perfect and improve the stability control system's design, architecture and operation. As an analysis of the function structure shows, the stability control system are structurally characterized with the redundant configuration of multi-series system and multi-system voting. The stability control system is complex in structure and large in the number of devices, so the Markov modeling is large in state-space number, which makes it impossible to realize the direct modeling solution. Based on the structural characteristics of the stability control system, the hierarchical Markov probability mapping method is proposed to reduce the number of state-space and the amount of computation, which makes it possible to realize the reliability analysis and calculation of the stability control system. The reliability modeling method is used to establish a detailed state model for a typical stability control system, which considers the factors of self-checking, overhauling, hidden faults and redundant configuration of the stability control system. The reliability analysis shows that unreasonable arrangement of equipment overhauling may reduce system reliability, which breaks the common knowledge that overhauling can improve the system reliability.

Analysis of Dynamic Performance of Phase Lock Loop and Its Effect on Line Relay

WANG Donghui, FANG Fang, LV Wentao, LUO Huafeng, YANG Tao, QI Xuanwei

2020, 53(3):  110-118.  DOI: 10.11930/j.issn.1004-9649.201806026

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The converters on the side of grid-connected renewable energy usually work on PQ mode. The phase lock loop (PLL) in the control system is the key component to determine the frequency of the terminal voltage. However, the PLL is designed based on normal operating conditions and the characteristics of the grid fault are generally not considered. The structure of the PLL is studied in this paper, and the characteristics of PLL are analyzed under the conditions of grid imbalance, frequency variation of voltage signal and multi-order signal input. On this basis, a wind farm equivalent model of 40 wind turbines are constructed, and the influence of PLL's performance on line protection is analyzed. It is found that when the wind farm's scale increases, the differential protection and distance protection will be affected in different degrees, but the 90° power directional element has a reliable performance. The analysis result can provide a reference for the selection and setting of line relay for large-scale integration of renewable energy.

Ground Fault Location of Large Generator and External Components

ZHAO Siteng, GUI Lin, ZHANG Qixue, WANG Xiangheng

2020, 53(3):  119-125.  DOI: 10.11930/j.issn.1004-9649.201910051

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A fault location method is proposed to distinguish the ground faults of large generators and their external components. It divides the generator and its external components into four regions:the generator, the high-voltage winding of excitation transformer, the high voltage winding of unit auxiliary transformer, and the remaining external components. According to the zero-sequence direction discrimination principle, the exclusion method is used to check and determine the location of the fault. The key to this location method is to measure the zero-sequence current of generator terminal and high-voltage side of excitation transformer/unit auxiliary transformer. It's necessary to select the TA according to different regions where the fault occurs. The location method was verified by a series of real fault cases, which proved that the method can accurately locate the ground fault of the generator and its external components, with shortened troubleshooting time and in-time power recovery of the generator. The proposed fault location method has the value of popularization and application.

Active Disturbance Rejection Control over Superheated Steam Temperature Based on Multi-objective Particle Swarm Optimization

NIU Haiming, YU Jiao, DING Changfu, WANG Zhaohui, TIAN Bin

2020, 53(3):  126-133.  DOI: 10.11930/j.issn.1004-9649.201908096

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Regarding the existing issues in the control of superheated steam temperature, which are related to the control system dynamic characteristics, such as large inertia, long duration of time lag and strong nonlinearities, as well as the difficulties to set the parameters of the controller under certain disturbances, this paper presents the cascade active disturbance rejection control-linear active disturbance rejection control (ADRC-LADRC) strategy. Specifically, in the outer loop the proposed method uses nonlinear active disturbance rejection control to reduce the overshoot, while in the inner loop it uses linear active disturbance rejection control to quickly respond to and then suppress the disturbance. At the same time, the multi-objective particle swarm optimization algorithm is used to optimize the parameters in the control loop. The test and engineering applications show that the ADRC-LADRC control strategy based on multi-objective particle swarm optimization algorithm has better control performance and strong anti-interference capability. Also it can quickly respond to disturbances and track the set values to keep the superheated steam temperature stable.

Calculation and Experimental Study on Purging Resistance of the Spiral Tube Heat Exchanger

LIU Junfeng, MA Xiaolong, LI Kang, CHEN Guangjian, ZHU Yingjie, MA Xiqiang

2020, 53(3):  134-138,146.  DOI: 10.11930/j.issn.1004-9649.201907165

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For the spiral tube heat exchanger with smaller diameter and more complex structure, using the conventional method is not an effective way to clean the inside of the tubes. In this paper, regarding the difficulties in cleaning the steam generator of high-temperature gas cooled reactor (HTGR), on the basis of the numerical model established for calculating the purging resistance of spiral tube heat exchanger, the effects of steam purging and compressed air purging are analyzed and compared respectively. Based on the calculation results, the compressed air is chosen as the purging media and then the purging process is tested and verified. The study results show that compressed air purging can meet the cleaning requirements of the relevant standards, while steam purging will probably make the tubes expand unevenly. Therefore, compressed air purging is recommended as the first choice.

The Present State and Prospect of Water Consumption in Coal-Fired Power Plants

LU Junchao, TAO Leixing, YUE Chunmei, CHEN Rui, LIU Zhichao, WANG Yanyan, ZHENG Fangdong, WAN Di

2020, 53(3):  139-146.  DOI: 10.11930/j.issn.1004-9649.201907169

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By summarizing the water balance test data and high-efficiency water-saving processes of typical coal-fired power plants, the water economic indexes such as water intake volume for unit power generation volume are analyzed to evaluate the water consumption level of power plants. The analysis results indicate that the power plants with lower water intake volume are characterized by advanced design concepts, effective management and reasonable reuse of wastewater. According to the calculation result, the water intake volume of coal-fired power plants (once-through cooling) can be lowered down even below 0.20 m³/(MW·h). Power plants of 1 000 MW class unit with flue gas condensation technology can produce 80~90 m³/h condensate water at full load in winter, which can be recycled back to the flue gas desulfurization system and industrial water system. As the approach of water system transformation in power plant tend to be more reasonable, the achievement of "zero replenishment of industrial water" technology can be expected in the near future.

Removal of Elemental Mercury from Coal Combustion Flue Gas Using Catalyzed Oxidation Method

QI Meng, ZHAO Yi

2020, 53(3):  147-153,166.  DOI: 10.11930/j.issn.1004-9649.201910092

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A liquid phase catalyzed oxidation system by Copper(III) periodate complex and Ni(II) was presented in this paper to oxide the insoluble gaseous Hg⁰ to soluble Hg²⁺ which could be removed easily by air pollution control devices (APCDs), such as wet flue gas desulfurization (WFDG). The key factors on removal efficiency of Hg⁰ were experimentally investigated and the results showed that the addition of Ni(II) could greatly improved the removal efficiency of Hg⁰. The average removal efficiency of Hg⁰ by parallel experiments was steadily at 93.3%, under the optimum conditions (DPC=0.18 mmol/L, Ni(II)=4×10^-5 mmol/L, T=45℃, pH=8.5). SO₂ in the flue gas had significant influence on Hg⁰ removal, especially under high concentration conditions, while NO in the flue gas only exhibited slight effects. Moreover, the active components in the reaction system and reaction mechanism were speculated from the analysis of oxidation product. The study proposed in this paper can provide valuable reference for further investigation in the development of new Hg⁰ removal techniques from coal combustion flue gas, especially in liquid phase catalyzed oxidation process.

Practice of Quality Assurance System of Carbon Dioxide Emission On-Line Monitoring System in the European Union

WANG Muhan, ZHU Lin, ZHANG Jingjie, YANG Fan

2020, 53(3):  154-158,176.  DOI: 10.11930/j.issn.1004-9649.201911010

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This paper concludes the quality control requirements of EU from the aspects of regulatory standards, data quality requirements and quality assurance, and compares them with the present situations in carbon dioxide monitoring and regulatory standards in China. Then, corresponding suggestions are proposed for China's thermal power plants on the application of continuous emission monitoring system (CEMS) to measure carbon dioxide emission and the establishment of complete standard and supervisory system in the next stage.

Global Renewable-Based Electrification Pathways and Its Long-Term Scenario Analysis

HONG Bowen, MIKETA Asami, GIELEN Dolf, RUSSO Daniel, JANEIRO Luis, BOSHELL Francisco, WAGNER Nicholas, TAIBI Emanuele

2020, 53(3):  159-166.  DOI: 10.11930/j.issn.1004-9649.201902114

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To meet the deep-decarbonisation need of a clean energy transition, the paper is dedicated to working out a blueprint of a renewable-based electrification future, in almost every aspects from its pathways to the potentials and benefits. Also the challenges it faces in industry, transport, and building sectors are analyzed and recommendations are proposed to cope with them in policy, technology, and market aspects. According to the results, it is not only technically feasible but also economically and socially beneficial to implement such a renewable-based electrification.

Optimization Method of Generation Rights Transaction Mechanism for Power System Accommodation Improvement

XU Haoliang, JIN Panrun, JIANG Jiheng, LU Zongxiang, QIAO Ying

2020, 53(3):  167-176.  DOI: 10.11930/j.issn.1004-9649.201907189

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With renewable energy consumption becoming a key issue, generation rights transaction between wind power and captive plants plays an important role in improving the power system's accommodation capacity. But there is no theory for evaluating and optimizing such mechanisms in the medium and long term. Based on probabilistic production simulation, this paper proposes a medium and long-term evaluation model to calculate system's accommodation capacity rapidly. The main factors affecting accommodation effect are summarized after analysis of operation mode of generation rights transaction. Considering the probabilistic characteristics of load and various power sources, an assessment model is constructed. Then, the shaping effect of the power generation rights transaction on the wind power probability curve is discussed, followed by analyzing the relationship between wind curtailment reduction and three key parameters:transaction capacity, start-up wind power and daily transaction time. The simulation results validate the effectiveness of the proposed algorithm in quick optimization and efficiency evaluation in monthly and annual scale.

Development and Application of Fast Reactive Power Control System for Large-Scale PV Power Plant

LI Zuming, XU Guangfu, CHEN Jun, WANG Chen, WANG Jian, JIANG Miao

2020, 53(3):  177-184.  DOI: 10.11930/j.issn.1004-9649.201911101

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At present, the AVC system of large-scale PV power plants is difficult to meet the needs of rapid control of voltage fluctuation due to its slow reactive power regulation speed and poor reliability. Therefore, a fast reactive power control system is designed based on GOOSE communication, and a time-sharing fast control method and an equal-margin reactive distribution strategy are proposed, and a fast reactive power controller is also developed. The test results show that the system has a reactive power control response time of less than 50 ms for the whole station, which can reduce or even replace the configuration of SVG, consequently saving the construction cost and land occupation for photovoltaic power plants.