Table of Content

05 August 2021, Volume 54 Issue 8

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Optimal Compensation Method for Multi-node Voltage Harmonics Based on SAPF

YIN Xiaoqing, YI Hao, YANG Zebin, ZHUO Fang, WANG Meng, LIU Xiayu, ZHU Chengzhi

2021, 54(8):  2-10.  DOI: 10.11930/j.issn.1004-9649.202007182

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With the decentralized access of non-linear loads in the local distributed network, the traditional shunt active power filter (SAPF) configuration method with the objective of local compensation of harmonics requires integration of a large number of control equipment, which leads to both low control efficiency and high control cost. Therefore, the optimization of SAPF configuration is needed for global comprehensive suppression of harmonics in the local distributed network. Firstly, the Norton equivalent method is used to establish an objective function for optimal compensation of the harmonic voltage in local distributed network. Secondly, the optimization problem is solved using the non-linear programming principle and the geometric aided analysis method to determine the installation position and optimal configuration capacity of SAPF in the system, and a comprehensive suppression algorithm is proposed for harmonic voltage in the power network based on SAPF. Finally, a simulation model of an IEEE-18 node system is established to verify the feasibility of the proposed algorithm. The results show that in the case of different distribution of nonlinear loads, all the configuration results have good control effects, and the overall harmonic distortion of the distributed network can be effectively suppressed through fewer SAPFs with less capacities.

Cost Estimation for Voltage Sag Control Based on Multidimensional Characteristics and Hausdorff Distance

LU Chengyu, HUANG Hongyang, XU Qunwei, HE Yujun, WANG Ying

2021, 54(8):  11-18.  DOI: 10.11930/j.issn.1004-9649.202007179

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Voltage sag control is non-standardized. Due to the lack of user-side details, it is hard to estimate the control capacity, which frequently causes excessive or inadequate sag controls. Considering the fact that the control object is affected by the multidimensional characteristics of voltage sags, we carry out a study on the problem of tolerance ability and control capacity identification of the control objects, and propose a Hausdorff distance identification method for sensitive equipment tolerance ability with consideration of the their sag multidimensional characteristics. By introducing the concept of pattern library, the fuzzy membership is used to judge the voltage tolerance ability of control objects. On this basis, an improved voltage sag severity index is put forward, and a control capacity identification method is proposed based on the improved sag severity index and control object capacity ratio. And then the required control cost is estimated. Based on the actual monitoring data of a city power grid, a case study shows that the proposed method is effective and reasonable, and is easy for practical application.

High Frequency Resonance Frequency Shift Method for Cable Distribution System

ZHU Mingxing, KONG Binbin, ZHANG Huaying

2021, 54(8):  19-26.  DOI: 10.11930/j.issn.1004-9649.202006235

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In order to solve the problem of high frequency resonance in cable distribution network, a high frequency resonance frequency shift method based on impedance reconstruction of distribution network is proposed. Firstly, an analysis is made of the mechanism of high frequency harmonic source and high frequency resonance in cable distribution network. Secondly, a high frequency resonance frequency shift method is proposed for impedance reconstruction of cable distribution network, and the frequency shift and resonance peak suppression effects are compared after reconstruction of different passive impedances. And then, based on actual project cases, the high frequency resonance suppression effects of the proposed method and its impact on the system stability are evaluated using the Bode diagram and root locus plotted with the system function, and the effectiveness of the proposed method is verified. Finally, the influence of passive impedance parameters on high frequency resonance of distribution network is studied.

An Analysis Method for Frequency and Transient Harmonics of Isolated Network Under Instable Condition

YANG Denghui, ZHU Mingxing, XU Bin

2021, 54(8):  27-34.  DOI: 10.11930/j.issn.1004-9649.202006213

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Focusing on the problem of spectrum leakage in Fourier harmonic analysis caused by rapid broadband changes in frequency and harmonics in isolated network under unstable condition, an analysis method for frequency and transient harmonics is proposed based on adaptive periodic sliding filter with variable bandwidth. Firstly, the high-frequency periodic interference of non-stationary signal is eliminated by the preprocessing system based on the principle of periodic sliding filter, and the DC component is separated. Then the preprocessed sequence is locked in real time by zero crossing method, and the bandwidth of the periodic sliding filter is adjusted adaptively. Finally, according to the real-time frequency of the calculated non-stationary signal, the non-stationary signal is divided into harmonics by the discrete Fourier transform (DFT) algorithm, and the transient information of each harmonic component is obtained accurately. Simulation results and field measurement data show that the method has high harmonic measurement accuracy under a variety of non-stationary states, and can effectively measure the frequency and transient harmonics of isolated network under the unstable state.

A Non-invasive Identification Method for Sensitive Load Based on Voltage Sag Monitoring Data

HU Chong, XU Bin, ZHEN Chao, ZHAO Xinde, WANG Xin, TANG Xingyong

2021, 54(8):  35-42,51.  DOI: 10.11930/j.issn.1004-9649.202007160

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For the problem that it is difficult to accurately obtain the user's sensitive equipment parameters and the production process structure in voltage sag mitigation, a method is proposed for identifying sensitive loads based on available voltage sag monitoring data. Discrete wavelet transform is performed on the voltage and current recorded when the voltage sag occurs to calculate the active power trajectory. The singular value decomposition method is used to identify the starting point of the transition section of the trajectory, and the characteristics of the trajectory and its relationship with the load voltage sag response are obtained. Combined with the voltage tolerance curve of sensitive equipment, the sag and load-response events are grouped. The active power and its recovery ratio after the end of the voltage sag is then calculated based on the recorded data, thereby the active power percentage of typical sensitive loads is identified. Through Matlab/Simulink simulation, the accuracy and validity of the proposed method and indexes are proved, which has obvious engineering significance.

Classification and Identification Method of Power Equipment for Industrial Users Based on Harmonic Emission Level

YANG Xingang, ZHANG Peng, DU Yang, PAN Aiqiang, XU Qin

2021, 54(8):  43-51.  DOI: 10.11930/j.issn.1004-9649.202007177

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With the rapid development of the power Internet of Things, clarification of user load status are significant for improving the quality of power supply service, power price decision-making, demand-side response, and paid precise services. The classification and identification of industrial power equipment based on non-intrusive methods is faced with the challenges of poor prior knowledge of industrial loads and low sampling frequency of the used data. Using the power quality monitoring data of large industrial users, this paper proposes a classification and identification method of power equipment for industrial users based on the level of harmonic emission. Firstly, a detection method is proposed for industrial equipment switching events based on bilateral cumulative sum algorithm. Secondly, the typical characteristics of each event is extracted to construct a feature matrix for industrial user equipment, and a feature screening method with high contribution rate is proposed to reduce the number of features. A classification and identification method of power equipment for industrial users based on k-means algorithm and silhouette coefficient is proposed. The 14-day power quality monitoring data of a rolling mill user under the 10 kV voltage level in Shanghai area was used to verify the proposed method. The result proves that the proposed method has high accuracy in classification of industrial user equipment with unknown equipment conditions, and has significant practical and promotion values.

An Internal Overvoltage Identification Method for Distribution Network Based on Transfer Learning

XU Hao, LIU Liqiang, LV Chao

2021, 54(8):  52-59.  DOI: 10.11930/j.issn.1004-9649.202006274

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As a measure for internal overvoltage identification of distribution network, the data driving method is limited in practical applications due to the small number of overvoltage samples. A transfer-learning-based deep convolutional neural network (D-CNN) algorithm is thus proposed to identify the internal overvoltage of distribution network. Firstly, 6 types of two-dimension time-frequency maps of 10 kV distribution network internal overvoltage are constructed by simulation and continuous wavelet transform (CWT). Then, the transfer-learning-based D-CNN network models are built using four network models, including Alexnet, Vgg-16, Googlenet and Resnet50. Finally, the two-dimension time-frequency maps are introduced into the transformed D-CNN for training. By comparing and analyzing the experimental results, it is found that the newly constructed VGG-16 network model has the highest identification accuracy, reaching 99.07%, which realizes the accurate classification of overvoltage faults in the case of scarce data.

Full-Model Electric Field Analysis of Flexible HVDC Converter Valve Hall with Fast Multipole Boundary Element Method

SHI Yuxin, WANG Zezhong, ZHAO Jiucai

2021, 54(8):  60-67.  DOI: 10.11930/j.issn.1004-9649.202003075

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The flexible HVDC converter valve hall has numerous equipment, complex structures and enclosed environment with coexistence of multiple medium, which makes the full-model electric field intensity analysis of the valve hall difficult in model building, large in calculation scale, and poor in efficiency with traditional methods. The symmetry fast multipole curved boundary element method (SFMCBEM) has the advantages of fast calculation speed and less memory consumption, and is suitable for solving large-scale problems. Two different structures of a ±160 kV flexible HVDC converter valve hall were modeled respectively and the SFMCBEM was used to calculate their full-model electric field with the number of nodes in calculation reaching up to 1.33 million. The influences of valve tower shielding system structure, bridge electric connection mode and valve hall arrangement on the surface electric field of fittings were analyzed, and the distribution characteristics of electric field in the valve hall were understood, which can provide a reference for equipment layout. The proposed method provides an effective means for understanding the electric field distribution in the flexible HVDC converter valve hall, and is of great significance for equipment insulation coordination design.

The Influence of UHVDC Additional Frequency Controller on Automatic Generation Control

WU Lingyun, HE Li, XIAO Xiong, TAN Chao, CHEN Gang, ZHOU Lin

2021, 54(8):  68-74.  DOI: 10.11930/j.issn.1004-9649.202005102

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The asynchronous interconnection of UHVDC in regional power grid has brought about the adaption problem of automatic generator control (AGC) strategy to UHVDC frequency control (FC). In order to analyze the influence of FC equipped in UHVDC on the AGC, the quasi-steady models of FC and AGC are used to find out the interaction mechanism between AGC and FC system. The power system full dynamic simulation (PSD-FDS) platform developed by China Electric Power Research Institute (EPRI) is applied to simulate the dynamic process of FC and AGC, and further analysis is made on the influence of FC on AGC both in the time domain and frequency domain, and some suggestions are proposed on optimization of the AGC strategy. The analysis results show that the fluctuation of frequency can be alleviated when FC is used, but the power loss of power systems needs to be compensated by AGC when serious fault occurs, it needs to be considered under the TBC mode that coordination of FC and AGC is set up to avoid the problems of AGC in re-regulation and slow recovery of frequency during serious faults.

A Nonlinear Dynamic Current Deviation Control Method for Suppressing Continuous Commutation Failures in UHVDC Systems

YUAN Bo, WANG Ying, SHAO Hua, ZHANG Qianmao, QIN Liangdong, LIU Ningning, DAI Zhihui

2021, 54(8):  75-82.  DOI: 10.11930/j.issn.1004-9649.202003188

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Aiming at the continuous commutation failures in LCC-HVDC systems, a nonlinear dynamic current deviation control method is proposed. The operation curve of current deviation controller is dynamically adjusted according to the severity of AC faults. Meanwhile, the nonlinear curve is used to replace the original linear curve to improve both the sensitivity of extinction angle increment to the current deviation, and the actual extinction angle margin, thus effectively suppressing the commutation failures of DC systems. The simulation results in PSCAD/EMTDC show that the proposed control method can effectively suppress the continuous commutation failures caused by various faults and can help the rapid recovery of DC system after faults.

An Efficient Positioning Algorithm Based on UWB and IMU Fusion in Electric Power Operation Scenes

YIN Kangyong, LIANG Wei, YANG Jibin, SUN Zhiming, ZHU Mengzhou, XIAO Peng

2021, 54(8):  83-90.  DOI: 10.11930/j.issn.1004-9649.202010061

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In complex environments such as electric power operation scenes, the performance of ultra wideband (UWB) positioning is seriously degraded due to non line of sight (NLOS) scenarios. The integration of UWB and inertial measurement unit (IMU) can improve the positioning accuracy, but there is error accumulation in IMU measurement, which requires accurate UWB measurement correction. Accurate identification and utilization of NLOS conditions is helpful to improve the positioning accuracy. In this paper, a UWB/IMU fusion algorithm based on extended Kalman filter (EKF) is proposed, which uses the distribution of UWB measurements in electric power operation scenes to determine NLOS conditions and mitigate errors, thus effectively improving the positioning accuracy under NLOS conditions. The proposed algorithm has good usability since it does not need prior knowledge of the environment and IMU correction. Theoretical and practical experimental results show that the performance of the proposed algorithm is superior to other baseline systems.

Three-Dimensional EGM Study on Shielding Failure Rate of Transmission Lines Considering Canyon Depth

BI Jieting

2021, 54(8):  91-97.  DOI: 10.11930/j.issn.1004-9649.202102077

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A considerable number of high voltage transmission lines are built across deep valleys. In the past, no specific study was carried out on the valley topography in building models for calculating shielding failure rate of transmission lines, and the shielding effect of the unique topography of valleys was ignored. In this paper, a new three-dimensional electrical geometrical model (EGM) based on valley depth is established to directly study the transmission line shielding failure rate through calculating the exposed and protected cambered surface areas. The effectiveness of the proposed three-dimensional EGM method is verified through an example, and the valley topography is proved to be one of the main causes for frequent lightning trip-out of transmission lines. Avoiding complicated calculus operation, the proposed method is mainly applicable in mountain valley area. With consideration of the canyon depth and the slope angle of the ground, the calculated shielding failure rate is closer to the actual situation, which is significant for application.

Modelling and Application of Electricity Marketing Tariff Risk Prediction Driven by New Forms of Distribution Networks

DAI Luping, QU Qing, HUANG Lu, PAN Ye

2021, 54(8):  98-102.  DOI: 10.11930/j.issn.1004-9649.202101015

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In the era of big data, digital transformation is being carried out for electric power companies. The role of distribution network would shift from satisfying basic load requirements to providing customers with personalized solutions, proposing high requirements for electricity marketing services. Electricity fee management has long become the main evaluation indicator for marketing quality services. The goal of this work is to build a universal model of tariff risk prediction based on big data techs and provincial features. In this regard, the risk of tariff and the operation costs would be controlled.

Impact of Large Number of Same Aggregated Distributed Generators on the High-Frequency Oscillatory Stability of a DC Microgrids

ZHANG Tianyi, ZHENG Kaiyuan, WANG Haifeng

2021, 54(8):  103-108.  DOI: 10.11930/j.issn.1004-9649.202105196

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The construction of DC micro-grid is conducive to the nearby absorption of renewable energy. Meanwhile, the increase of power electronic devices in the micro-grid may lead to the occurrence of high-frequency oscillations and other phenomena, which requires the evaluation of the stability of small disturbances during planning. In the evaluation process, the number of micro-power source is approximately proportional to the dimension of the system state matrix, so a large number of micro-power source connections bring challenges to modal calculation. It is necessary to propose a method of order reduction to meet the requirements of small disturbance stability analysis of DC microgrid. The aggregated reduced order model for high frequency oscillations can reduce the workload of numerical calculation in the process of modal analysis of microgrids, which is helpful for better evaluation of microgrids in the planning stage. In the last part, simulations are carried out to verify the method for different micropower access quantity and different microgrid topology. The simulation results show that the method proposed in this paper can effectively evaluate the high frequency oscillation risk of DC micro-grid and simplify the difficulty of calculation.

Calibration Methods for Junction Temperature Measurement of High Power IGBT Modules

CHEN Jie, DENG Erping, ZHAO Zixuan, YING Xiaoliang, HUANG Yongzhang

2021, 54(8):  109-117.  DOI: 10.11930/j.issn.1004-9649.201910055

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The accuracy junction temperature measurement is of great significance for condition monitoring and reliability assessment of power IGBT devices. The junction temperature measurement method using saturation voltage drop at small current is the most widely used method and is recommended by various test standards. Calibration is the first step of this method and also the basis of junction temperature measurement. The traditional calibration method has the problem of applicability and accuracy for high power IGBT modules. Firstly, the accuracy of two commonly used calibration systems is discussed and compared, and a new calibration system based on electromagnetic heating is proposed, and its accuracy is verified by experiment. Secondly, the non-linearity of calibration curve is discussed and analyzed, and the necessity of calibration at full temperature range and polynomial fitting is pointed out, which further complements the calibration method. This paper can provide a methodology guidance for calibration of high power IGBT modules.

Analysis on High Temperature Corrosion of Water-Wall in a 440 t/h Boiler Under Low-NO_x Combustion Mode

WANG Yibin, ZHANG Sicong, TAN Houzhang, LIN Guohui, WANG Meng, LU Xuchao, YANG Hao

2021, 54(8):  118-127.  DOI: 10.11930/j.issn.1004-9649.202004109

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The corrosive products that were collected from water-wall tubes close to burners at the lowest layer in a 440 t/h coal-fired furnace, were characterized by various technology methods including X-Ray Fluorescence spectrum (XRF), X-Ray power Diffraction (XRD), Scanning Electron Microscope and Energy Dispersive System (SEM-EDS), for the analysis and discussion of the formation of corrosive products and enrichments of trace elements. The results showed that inner corroded layer was mainly composed of FeS₂, Fe₂O₃, PbS and ZnS, with higher enrichment of Pb element than Zn. While in the outer corroded layer, ZnS, PbS, GaS, Fe_1-xS and Zn_1.0Al_1.04S_2.13 were the major compositions of the mineral phases with minor elements of Ga, Se and Bi, but more significant enrichment of Zn and Ga elements were observed than that in the inner corroded layer. Trace elements including Pb, Zn, Ga, Se, Ge, As, Bi, Th, Sn, Sb were enriched both in inner and outer corroded layer. They were formed mainly via the vaporization-condensation of gaseous species from coal combustion and the release from the unburned carbon particle that adhered to water-wall tube surfaces. Moreover, some of condensed trace elements may re-vaporize and then diffuse into deeper corrosion layer, which would further cause the growth of the crack opening size in corrosion. During the corrosive process, the oxidation and sulfidation reactions of iron matrix occurred simultaneously and competed with each other. The cracks were first formulated at the corroded layer adjacent to iron matrix and then as the cracks developed, it started to break into small patches. Various kinds of pyrrhotite with different crystal sizes would be generated and some gaseous sulfur would be released as the pyrite migrated toward the outer layer, which suggests that gaseous sulfur may play an important role in corrosive process. Additionally, the migration and diffusion of fine particles and gaseous trace elements into iron matrix side may further accelerate the rate of internal stress cracking, to promote the diffusion of corrosive gases and aggravate the corrosion.

Life Cycle Modeling Analysis of the Interaction Between Carbon Dioxide and Air Pollutant Emissions of Coal Power in China

WANG Yanzhe, ZHOU Sheng, YAO Zilin, OU Xunmin

2021, 54(8):  128-135.  DOI: 10.11930/j.issn.1004-9649.202102023

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Coal power occupies a dominant position in China's power supply structure, and its environmental impact has been the hotspot for research. This study established a life cycle analysis model for CO₂ and air pollutant emissions of coal power in China, built a database of coal-power’s parameters based on literature review and calculated the emissions per kW·h. The results show that the average life cycle CO₂ emissions per kW·h from China’s coal power is 838.6 g/(kW·h) in recent years, and the SO₂, NO_x, and PM_2.5 emissions are 0.34 g/(kW·h), 0.32 g/(kW·h), and 0.08 g/(kW·h), respectively. The air pollutant emissions per kW·h have fallen by more than 90%, mainly due to the ultra-low emission transformations of coal power in China. Research also indicates that the air pollutant emissions from the coal power can be effectively reduced by increasing the single-unit capacity and carrying out ultra-low emission retrofits, and the CO₂ emissions can be reduced to 144 g/(kW·h) by use of the carbon capture and storage (CCS) technology for coal-fired power, which can help achieve the carbon neutralization goal in China. If stricter air pollutant emission standards and treatment methods are not adopted, the CCS technology may increase the air pollutant emissions per kW·h from coal fired power by about 30% to 40%, which is related to the technology used in the carbon capture process.

SVR Data-Driven Optimization of Generator Leading Phase Operation Limit

LI Dengfeng, YANG Mincai, LIU Yuming, XU Ruilin, YU Xia, LI Zhaojiong

2021, 54(8):  136-143,153.  DOI: 10.11930/j.issn.1004-9649.202004105

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In view of the difficulty in modeling the mechanism caused by the complex and strong coupling nonlinearities between the multiple variables in the limiting conditions of leading phase operation, a novel method is proposed in this paper to optimize the leading phase operation limit of generator based on data-driven support vector machine regression (SVR). The limit calculation of generator leading phase operation is converted to the minimization of reactive power subject to the multiple constraints of leading phase. Based on the generator power angle equation, the objective function equation of reactive power is established. In order to formulate the constraint equation model, the nonlinear mapping relationship between constraint variables and independent variables in the objective function is constructed based on SVR data-driven model. The improved second-order oscillation particle swarm optimization algorithm is then applied to solve the optimization model. The case studies show that in addition to its modelling simplicity, the proposed method has exhibited high accuracy and strong adaptability, for the purpose of fast calculation of the generator leading phase limit under the conditions of any given active power output. Therefore it can be used for the online modeling and monitoring of the margin of generator leading phase operation.

Day-Ahead and Intra-day Scheduling Strategy of Concentrated Solar Power Station with Thermal Energy Storage and Wind Farm Considering Coordination Between Generation and Load

LIU Xinyuan, CHENG Xueting, BO Liming, ZHANG Jiarui, ZHENG Huiping, HAO Jie

2021, 54(8):  144-153.  DOI: 10.11930/j.issn.1004-9649.202004040

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At the moment, the problem of wind curtailment in the Northwest is still serious. In this context, to improve the wind power accommodation of a system, this paper combines the adjustable resources on both sides of generation and load in the Northwest and proposes a day-ahead and intra-day scheduling strategy of the concentrated solar power (CSP) station with thermal energy storage (TES) and a wind farm considering coordination between generation and load. Firstly, considering the energy shifting of the CSP stations and the long response time of residential load, a day-ahead scheduling model has been constructed with price-based demand response (PDR) and the aim of minimizing the operation cost and the wind curtailment in day-ahead scale. Then, given the flexible adjustment ability of the CSP stations and the short response time of intensive energy loads, this paper has built an intra-day scheduling model for the minimal adjustment cost and the wind curtailment in intra-day scale according to the day-ahead scheduling plan and the intra-day wind power forecast. The simulation results show that the proposed strategy can promote wind power accommodation while reducing system cost by making full use of the adjustable resources on both sides of generation and load and their characteristics.

Comprehensive Evaluation of Operation and Maintenance of Distributed Photovoltaic Power Based on Interval Intuitionistic Fuzzy Group Decision

ZUO Gao, ZHANG Chao, CHEN Yuchun, YU Haibo, LU Yudong

2021, 54(8):  154-163.  DOI: 10.11930/j.issn.1004-9649.202005145

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Aiming at the current situation that the evaluation index system and information for operation and maintenance management of distributed photovoltaic power stations are imperfect, this paper studies the comprehensive evaluation for operation and maintenance management of distributed photovoltaic power stations based on interval intuitionistic fuzzy group decision-making. Firstly, the key factors that affect the intelligent operation and maintenance management of distributed photovoltaic power stations are analyzed. Then, a multi-dimensional evaluation indicator system and its calculation method are proposed with a comprehensive consideration of economic, social, and technical factors. Considering the fact that the proposed indicators are various in types, extensive in contents, numerous in contact personnel, which leads to the complexity and incompleteness of acquisition data, the interval intuitive fuzzy group decision-making method is employed for comprehensive evaluation of the intelligent operation and maintenance management in order to reduce the information loss or distortion and correctly characterize the decision-making information of group decision-making experts. Simulation examples have verified that the proposed method can obtain effective evaluation results under the conditions of missing or incomplete information of photovoltaic power stations, which will be feasible for the actual operation and maintenance of distributed photovoltaic power stations.

Optimization Planning on Power System Supply-Grid-Storage Flexibility Resource for Supporting the “Carbon Neutrality” Target of China

JIN Chen, REN Dawei, XIAO Jinyu, HOU Jinming, DU Ershun, ZHOU Yuanbing

2021, 54(8):  164-174.  DOI: 10.11930/j.issn.1004-9649.202012126

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In September 2020, China proposed to striving to achieve carbon neutrality by 2060. It is an important way to achieve carbon neutrality by vigorously developing a power system with high penetration of wind and photovoltaic (PV) solar energy. Due to the fluctuating and intermittent nature of new energy power generation, it is necessary to improve the flexibility of the power system to guarantee the safe, stable and economic operation of the clean energy power system. With the 2060 carbon neutrality target as the boundary and an incorporated 8760-hour-time-series operation simulation model, we optimize the new energy power, energy storage and grid interconnection capacity from different time and space scales, considering various flexibility resources constraints, thereby offering a viable way to carbon neutrality. On this basis, the sensitivity analysis on wind and PV power curtailment, wind and PV power capacity, energy storage and grid interconnection capacity are completed to further demonstrate the effectiveness of the proposed model and method, and the benefits of coordinated supply-grid-storage planning are quantitatively analyzed for the high new energy penetrated power system.

Analysis of Relay Protection for Offshore Wind Power Long-Distance Submarine Cable Transmission with High Resistance Station

TAN Zhenlong, QIAN Xiangyi, CAI Wenchang

2021, 54(8):  175-181.  DOI: 10.11930/j.issn.1004-9649.202104016

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China’s current long-distance offshore wind power mainly follows a high-voltage AC transmission mode with an additional mid-range high-resistance compensation station. With regard to the problem about protection configuration for offshore wind power long-distance submarine cable transmission with the high resistance station, the relay protection configuration scheme and action logic are analyzed with a typical case. The reliability of range fault protection for submarine cables is studied, and then the impact of voltages at different measurement points taken by the offshore high resistance station on the calculation of capacitive current compensation is analyzed. In addition, the necessity of collecting the voltage on the offshore high-resistance side to calculate the differential compensation current is verified by simulation. The simulation results show that for the fault within the protection range, compared with collecting the actual voltage on the high-resistance side, taking the line-side voltage instead has a certain impact on the compensation current calculated by the protection device. To reduce the error in calculating the differential compensation current, the protection device should collect the voltage of the high-resistance station to calculate the differential compensation current and then work out the differential current after compensation to correct capacitive and reactive current.

Mix Copula Function Based Wind Power Correlation Analysis: A Bayesian Linear Regression Approach

SU Chenbo, LIU Chongru, XU Shitian, YUE Hao

2021, 54(8):  182-189.  DOI: 10.11930/j.issn.1004-9649.201907121

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Analyzing the output correlation among wind farms is beneficial to reasonably plan the power transmission and scheduling optimization, so as to improve the utilization rate of transmission lines. Taking wind field in northern Hebei region as an example, this paper analyzes the characteristics of wind power first, and then improves a mix Copula method to model the relationship among the wind power correlation structure. What’s more, we use the Bayesian linear regression method to establish a mixed Copula function model to calculate the correlation of wind speed sequences from different wind farm groups. In this way, we can fit the joint distribution function between them and analyze the impact of correlation on the joint output of wind farms. In addition, this method has been verified to be effective and accurate, it was also be compared with other correlation function modeling. The results show that the mixed Copula function model based on Bayesian linear regression can well calculate the correlation of wind power output, from which the output probability distribution obtained can get more accurate fitting results.

Demand Analysis of Energy Storage for the 14th Five-Year Plan Period Based on Time Series Considering Power System Flexibility

REN Dawei, JIN Chen, XIAO Jinyun, HOU Jinming, DU Ershun, ZHOU Yuanbing

2021, 54(8):  190-198.  DOI: 10.11930/j.issn.1004-9649.202007255

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During the "14th Five-Year” period, the rapid growth of installed capacity of wind power and photovoltaic systems will intensify the fluctuation of the system net load. It is inevitable that the demand for flexible resources such as energy storage will continue to rise. Meanwhile, as the energy storage technology is becoming more mature and the cost continues to fall, it tends to be gradually applied to every aspects of the power system. Therefore, it is necessary to establish an energy storage optimization planning model which takes into account the demands of system flexibility to evaluate the demands of China's energy storage in the next five years more scientifically. This article first proposes the operation simulation model method and energy storage demand analysis process based on the time sequence curve considering the flexibility of the power system. Specifically, by taking the minimization of total system cost as the optimization objective subject to the investment decision constraints and operation constraints, the structure and capacity of energy storage for the target-level year are coordinated and optimized. Secondly, based on the proposed model and methods, the optimal energy storage capacities under the protocol power transmission mode for China's seven regional power grids in 2025 are calculated respectively. The configuration of energy storage are analyzed and comparative analysis of energy storage capacity under the flexible adjustment mode is also carried out. Finally, based on the above analysis, we summarized the conclusions regarding China’s power system energy storage capacity, new energy generation capacity, wind curtailment and solar curtailment rate, and comprehensive electricity cost during the “14th Five-Year” period, which will provide technical support for the planning of energy storage in the next five years.

Experimental Research on Photovoltaic Arrays Output Power Enhancement Experiment Under Partial Shading in Frigid Plateau Region

ZHAO Bin, TAN Heng, LIANG Gao, DONG Xiaodong, QU Hongwei, WANG Li, ZHOU Lawu

2021, 54(8):  199-208.  DOI: 10.11930/j.issn.1004-9649.202103051

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By taking advantage of the photovoltaic (PV) power generation technology, the abundant solar energy resource in frigid plateau region can greatly improve the local energy infrastructure. However, the low efficiency of PV power plant has been existing as a widely publicized technical barrier. Specifically, the aging of PV modules, high surface temperature or partial shading may severely undermine the output of PV power plant. In this paper, take the example of the 4×2 PV arrays, based on the modeling and simulation with Matlab/Simulink software, the output characteristics of PV arrays are compared with respect to different structures under partial shading conditions. The results show that the RTCT structure outperforms all three others, with its maximum output power of PV array increased by 7.7% on average, such that the foundation for experiments is then formulated on enhancing PV arrays output power. Base on the experimental platform of PV arrays output power enhancement built in Lasa, the PV arrays output power enhancement technology is developed in terms of two methods, i.e., changing the topological structure of PV arrays and adding DC optimizers. The results show that both methods can increase PV arrays output power, which can provide solutions for optimization design and operation of PV power plant.