ISSN 1000-1026
CN 32-1180/TP
  • ISSN 1000-1026
  • CN 32-1180/TP

Volume 43,Issue 6,2019 Table of Contents

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Review on Case Filtering in Transient Stability Analysis
XUE Yusheng, HUANG Tiangang, CHEN Guoping, ZHENG Yuping, WEN Fushuan, XU Yan and ZHAO Junhua
2019, 43(6): 1-14.DOI: 10.7500/AEPS20181008004
[Abstract](442)[HTML](0)[PDF 1.52 M](255)
Abstract:
In the case filtering link, as many stable and unstable cases as possible can be identified rapidly through qualitative machine learning or quantitative approximate analysis so that the number of cases requiring detailed analysis and the total computational burden can be reduced. This paper discusses the adopted assumptions, characteristic variables, classification rules and generalization ability of case filtering in transient stability analysis. The integration of data driven and model driven is analyzed, which includes the introduction of causal elements, the deep integration of data statistic paradigm and model simulation paradigm for knowledge extraction. Based on the stability mechanism, a two-layer classifier is proposed: the lower layer contains several parallel links, and each link utilizes quantitative algorithm with different degrees of approximation. Their output data are regarded as the input of the upper layer. According to the approximate causality, it can reflect the influence of most original data on transient stability. Therefore not only the correct recognition rate and robustness of the classifier can be both enhanced, but also the error mechanism, evaluation credibility and acceptability can be revealed.
Cyber Energy Systems
Quantitative Survivability Assessment of Power Cyber-Physical System Considering Optimized Load Redistribution
QU Zhaoyang, DONG Yunchang, QU Nan, LIU Yaowei, YIN Xiang'ai and LI Guisen
2019, 43(6): 15-24.DOI: 10.7500/AEPS20180720006
[Abstract](200)[HTML](0)[PDF 1.51 M](111)
Abstract:
Because the scale of power cyber-physical system(CPS)is growing, and the existing cascade failure model ignores the information flow and the power flow transfer characteristics, it is difficult to quickly and effectively assess the survivability. Aiming at this problem, this paper proposes a quantitative survivability assessment method of power CPS considering load optimized redistribution. Firstly, according to the system topology and association, the degree-media weighted correlation matrix of power CPS is established by defining the degree function and the electrical interface, and the formal representation of coupled CPS is realized. Then, based on the structural connectivity change and risk propagation range of CPS cascade failure, the survivability assessment model is designed based on the constraints such as node load capacity limitation, optimal allocation strategy of information flow, power flow optimization equation and system safety operation. Finally, the chaotic Lévy search firefly algorithm is proposed to efficiently solve the assessment model. The case study shows that the assessment method can effectively quantify the survivability of power CPS and improve the assessment efficiency of large-scale coupled systems.
Second-order Cone Programming Based Probabilistic Optimal Energy Flow of Day-ahead Dispatch for Integrated Energy System
ZHANG Bowen, SUN Yonghui and ZHANG Shida
2019, 43(6): 25-33.DOI: 10.7500/AEPS20180510004
[Abstract](239)[HTML](0)[PDF 1.46 M](116)
Abstract:
With the aggravation of energy crisis, re-electrification has become an inevitable choice to solve the problem of energy development. Taking gas-electric integrated energy system(IES)as a new way of re-electrification, second-order cone programming(SOCP)is proposed to solve the probabilistic optimal energy flow of the day-ahead dispatch of IES. Firstly, the day-ahead dispatch of IES model consists of the electric power system(EPS), the natural gas system(NGS)and the energy hub(EH). Then, the day-ahead dispatch of IES model is changed into a convex model and the point estimation method is used to solve the probabilistic optimal energy flow of the day-ahead dispatch. Finally, a typical case study indicates that the algorithm is correct and effective on the YALMIP platform in MATLAB.
Basic Research
Analysis on Pattern of Power System Cascading Failure Based on Sequential Pattern Mining
LIU Yuhang, HUANG Shaowei, MEI Shengwei and ZHANG Xuemin
2019, 43(6): 34-40.DOI: 10.7500/AEPS20180528009
[Abstract](206)[HTML](0)[PDF 1.56 M](127)
Abstract:
Studying the propagation mechanism of cascading failures is of great significance for identifying the vulnerable lines in power grid and formulating prevention and blocking strategies for cascading failures. Based on analyzing the development progress of cascading failures, the concept of cascading failure pattern is defined. A cascading failure pattern mining algorithm(CFPMA)based on sequential pattern mining technology is proposed to analyze massive simulation data and identify critical cascading failure pattern of power system. Finally, taking the IEEE 39-bus system and a real provincial power system for example, CFPMA is used to mine the main cascading failure patterns, and the cascading failure propagation law is analyzed by combining the power grid topology and power flow. The test results show that the proposed method has a good effect on identifying the main cascading failure patterns and the vulnerable lines.
Impedance Modeling and Sub-synchronous Resonance Mitigation Strategy of Doubly-fed Induction Generator Based Wind Turbine in Static Reference Frame
ZHANG Xueguang, QIU Wangming, FANG Ran, ZHU Lin and XU Dianguo
2019, 43(6): 41-48.DOI: 10.7500/AEPS20180824002
[Abstract](187)[HTML](0)[PDF 1.55 M](128)
Abstract:
To explain the mechanism of sub-synchronous resonance(SSR)in doubly-fed induction generator(DFIG)based wind turbine system under series compensation, a static reference frame impedance model of DFIG based wind turbine is established. Firstly, the dq impedance model of DFIG based wind turbine is transformed into complex vector form and its frequency-domain impedance model is derived by frequency transformation. Based on the physical interpretation represented by the impedance model, the influence of controller and network parameters on equivalent impedance and SSR frequency of grid-connected system is analyzed using equivalent RLC series circuit. Damping control and virtual inductance control are proposed to mitigate SSR, which can increase the damping of SSR region and reduce the SSR frequency of the system, respectively. Finally, the accuracy of the model and theoretical analysis is verified by simulation.
Power Prediction and Correction Model Considering Wind Power Ramping Events
YE Lin, LU Peng, TENG Jingzhu, ZHAI Bingxu, WU Linlin, LAN Haibo and ZHONG Wuzhi
2019, 43(6): 49-56.DOI: 10.7500/AEPS20180321004
[Abstract](233)[HTML](0)[PDF 1.42 M](182)
Abstract:
With the integration of large-scale wind power into power system, wind power ramping events(WPREs)have brought series of effect on the stability and safety for power system operation. It is becoming more and more urgent to study the power prediction when the ramping event occurs. Ultra-short-term prediction and correction model considering the WPREs is employed based on extreme learning machine(ELM). Firstly, the optimized swinging door algorithm is utilized to identify the WPREs and extract the feature value of WPREs. Then, the fuzzy C-means clustering model is established to obtain the congeneric data. On this basis, by using ELM to train and predict the data mentioned above, similar ramping events to the results of current wind power prediction are found from historical WPREs library by tuple vector time warp(TVTW)algorithm, which obtains historically similar ramping events of power prediction. Finally, the wind power prediction result is corrected corresponding to the difference between the historical value and the actual value of predicted power. Case studies show that the proposed method can accurately identify WPREs and significantly improve the precision of ultra-short-term forecasting for wind power.
Capacity Configuration Method of Phase-change Energy Storage and Expander Generating System in Wind Farm
ZHU Sanli, LU Jiping, LIU Jialin and GE Jinjin
2019, 43(6): 57-63.DOI: 10.7500/AEPS20171222001
[Abstract](137)[HTML](0)[PDF 1.41 M](122)
Abstract:
To improve the sustainable running ability of the wind power generation and energy storage system, a modified phase-change energy storage and expander generating system(PESES)is proposed. The optimization method of the system capacity configuration is analyzed. Firstly, the historical annual mean wind power data are resolved based on the median-filtering algorithm. The difference between the stable component of the actual output in the wind farm and the dispatch order is calculated to formulate the fractional frequency control strategy. Secondly, the non-parametric estimation is used to calculate the optimal power level of the PESES under which the given wind power schedule ability confidence level is satisfied. The evaluation index of the sustainable operation capability for the energy storage system is defined. Meanwhile, the comprehensive economic evaluation function consists of the investment costs of the power exchanging, the energy supporting and the sustainable operation safeguard of the system. On the basis of the evaluation index and the evaluation function, the optimal energy capacity of the PESES is planned. Finally, an example of the operation and planning of a wind farm equipped with a steam-jet double-screw expander generating system is described.
Abnormal Data Identification Algorithm for Photovoltaic Power Based on Characteristics Analysis of Illumination Process
YANG Mao and HUANG Xin
2019, 43(6): 64-69.DOI: 10.7500/AEPS20180626003
[Abstract](152)[HTML](0)[PDF 4.11 M](86)
Abstract:
High quality of photovoltaic(PV)power data is the basis for conducting PV research, but the data collected from PV power plants contains a large proportion of abnormal data, which need to be identified. The PV power data with different illumination characteristics is modeled separately, and the probability distribution function of irradiance and power is constructed by the Copula joint distribution function. The BFGS parameter estimation method based on empirical function is used to estimate the parameters of various Copula functions. Refer to various Copula functions, Euclidean distance of empirical joint distribution function and K-S values, the Copula function is selected. The probability power curve under 90% confidence of the probability distribution of the PV power condition is obtained by combining the narrowest principle of the estimation interval. According to engineering experience and considering the time series characteristics of abnormal data, an abnormal data recognition model is established based on the criteria of four types of abnormal data. The simulation analysis of raw data and synthetic abnormal data of PV power station shows that the proposed method can identify various types of abnormal data effectively and accurately.
Analysis of Economic Influence Factors in Wind/Photovoltaic/Storage Microgrid
XIE Hua, TENG Xiaofei, ZHANG Yanjie, ZHENG Tianwen and CHEN Laijun
2019, 43(6): 70-76.DOI: 10.7500/AEPS20180201004
[Abstract](202)[HTML](0)[PDF 1.41 M](164)
Abstract:
The wind/photovoltaic/storage microgrid(MG)is an effective solution which achieves complementary advantages and efficient use of distributed sources. However, many factors affect the economics with various influences. The criticality of economic factors is quantified and analyzed in the wind/photovoltaic/storage MG. Based on the analysis of operation mode, the economic model of MG planning is built. The model is aimed at optimal annual net profit considering the operation characteristics of micro-sources, the power balance between the MG and the utility grid as well as the reliability constraints. Also, the evaluation indices of economic operation are established. On this basis, economic factors in both planning and operation aspects are quantified by calculating the influence coefficients. A practical MG in Yunnan Province is used as case study. The analysis results show that rational allocation of energy storage can improve the economics of MG planning, and the key economic factors of wind/photovoltaic/storage MG include the equivalent life cycles of energy storage, the unit investment cost of wind generators and the discount rate on the planning level, and the energy supplied, unit electricity price as well as unit environmental benefit of wind power and photovoltaic generation on the operation level.
Power Supply Capability Evaluation of Active Distribution Network Considering Reliability and Post-fault Load Response
GE Shaoyun, SUN Hao, LIU Hong, ZHANG Qiang and LI Jifeng
2019, 43(6): 77-84.DOI: 10.7500/AEPS20180806006
[Abstract](170)[HTML](0)[PDF 1.51 M](138)
Abstract:
The traditional method of power supply capability(PSC)evaluation is simply based on the network-wide N-1 criterion at peak load time and fails to consider the impact of distributed generator(DG), energy storage and load response. To solve this problem, this paper proposes a new PSC evaluation method of active distribution network(ADN)considering flexible reliability demand and post-fault load response. Firstly, combined with the uncertainty of DG output and the difference of users' response capability, the DG, energy storage and responsive load in ADN are modeled. Secondly, a PSC evaluation model is constructed with the objective of maximizing the PSC of ADN under the constraints of reliability demand and load response economy. Thirdly, a quasi-sequential Monte Carlo simulation method is developed for reliability assessment of ADN considering distributed photovoltaic, battery and demand response, and a solving method of PSC evaluation model based on genetic algorithm is proposed. Finally, the results of a typical ADN case study show that the proposed method can effectively tap PSC and improve the efficiency of asset utilization.
Generalized Fast Decoupled Load Flow Algorithm
CHEN Yanbo, ZHANG Zhi, XU Jingqiang, ZHOU Meng, YU Rui and LING Liang
2019, 43(6): 85-91.DOI: 10.7500/AEPS20180515009
[Abstract](210)[HTML](0)[PDF 1.31 M](109)
Abstract:
Fast decoupled load flow(FDLF)algorithm has been widely used in the domestic and international power dispatch and control center and planning department. The FDLF algorithm usually has very high computational efficiency. But for the transmission networks and distribution networks with high resistance-to-reactance ratios, the mathematical basis of the FDLF algorithm is no longer satisfied, and its convergence and computational efficiency are poor. So the FDLF algorithm cannot be applied to the transmission networks and distribution networks with high resistance-to-reactance ratios. The above problem is addressed by transforming active/reactive power at buses so that they can be classified as quasi active/reactive power at buses, which have better decoupling characteristics. And this decoupling property is independent of the value of resistance-to-reactance ratio. On this basis, a generalized fast decoupled load flow(GFDLF)algorithm is proposed. The GFDLF algorithm is based on only one assumption, rather than three assumptions used in the conventional FDLF algorithm. As a result, the GFDLF algorithm has good adaptability to both power transmission network and distribution network(including the network with high resistance-to-reactance ratio). Simulation results show the effectiveness and efficiency of the proposed method.
Performance Analysis and Improvement of Newton Method for Power Flow Calculation of Large-scale Integrated Transmission and Distribution Network
TANG Kunjie, DONG Shufeng, ZHU Bingquan and SONG Yonghua
2019, 43(6): 92-99.DOI: 10.7500/AEPS20180428001
[Abstract](175)[HTML](0)[PDF 1.32 M](94)
Abstract:
In order to meet the demand of integrated power flow calculation speed, an improved Newton method is proposed. In view of the seriously ill-conditioned Jacobian matrix and poor convergence and so on, an adaptive Levenberg-Marquardt method is used to choose the initial values, and incomplete LU decomposition method is used to preprocess Jacobian matrices, which effectively guarantees the numerical stability and improves the convergence of Newton method. To solve the problem of large-scale and low computing efficiency after integration of transmission and distribution networks, the GPU parallel acceleration technology is used to accelerate some steps with intensive computation including the formation of Jacobian matrix, matrix-vector operation and so on. The numerical experiments show that, the proposed algorithm can significantly improve the speed and accuracy of the large-scale integrated transmission and distribution networks, and it has a strong universality for different situations such as multiple distribution network areas, distribution network with loops or distributed generators, ill-conditioned systems.
Decentralized Economic Dispatch for Power System Based on Alternating Direction Method of Multipliers
XIA Shiwei, ZOU Weiwei, ZHANG Qian and LI Gengyin
2019, 43(6): 100-106.DOI: 10.7500/AEPS20171228005
[Abstract](188)[HTML](0)[PDF 1.60 M](165)
Abstract:
As more and more distributed generators(DGs)are connected to the modern power systems in a distributed manner, the conventional centralized economic dispatch approach has limitations such as heavy computational burden, high communication complexity and lack of flexibility. Therefore, this paper proposes a decentralized economic dispatch approach for power system based on the alternating direction method of multipliers(ADMM), which comprehensively considers the fluctuation characteristics of wind power, the DG dynamic model and its generation cost. In each iteration of the proposed approach, it only needs to collect the whole system net load and the average active power of DGs, thus all DGs could independently seek the optimal solution of active power in parallel. Finally, a distribution network consisting of multiple DGs is tested in MATLAB/Simulink to validate the performance of the proposed approach in the case of wind power fluctuations and real-time load changes. Comparative results with the conventional centralized economic dispatch approach have confirmed the accuracy and validity of the proposed approach.
Application Research
Analysis on Virtual Torque and Oscillation Instability Mechanism of Virtual Synchronous Generator with Reactive Power-Voltage Controller
LIU Ni, ZHANG Changhua, LIAO LI, CHEN Xin, CHEN Shuheng and LIU Qunying
2019, 43(6): 107-115.DOI: 10.7500/AEPS20180608005
[Abstract](322)[HTML](0)[PDF 1.40 M](145)
Abstract:
Virtual synchronous generator(VSG)has become an attractive scheme for connecting inverters with grids by simulating electromechanical transient process of synchronous generators. However, there also exists power oscillation problems in the VSG, and the related research on oscillation mechanism is needed. Based on the theory of torque analysis in the traditional power system, this paper establishes a small-signal model of VSG with reactive power-voltage controller. Combined with the oscillation mode, the virtual torque coefficient is redefined. Then the relationship between the virtual torque coefficient and VSG stability is analyzed. It is mathematically proved that the lack of virtual damping torque will lead to power oscillation instability of VSG. Taking the VSG with robust droop control as an example, the calculation method of virtual torque coefficient is given, and the conclusion is verified through PSCAD/EMTDC simulation and physical experiment. Finally, this paper discusses the effect of VSG with reactive power-voltage controller on the virtual torque coefficient and system small-signal stability from different perspectives, such as the initial state of the system, line parameters and controller parameters. The research is beneficial to the VSG controller design and the system small-signal stability analysis.
Impedance Analysis and Sub-synchronous and Super-synchronous Oscillation Suppression of Modular Multilevel Medium Voltage Converter
GAO Shang, WANG Jianhua, LI Zhou, LI Lingyu, HE Guoqing and LI Guanghui
2019, 43(6): 116-121.DOI: 10.7500/AEPS20180515005
[Abstract](167)[HTML](0)[PDF 1.34 M](115)
Abstract:
Modular multilevel converter(MMC)is suitable for grid-connected interface for medium and high voltage power grids. For the potential sub-synchronous and super-synchronous oscillation problem in photovoltaic(PV)medium voltage direct current(DC)power collection system, the positive and negative sequence impedance models of MMC converter are systematically established and the basis of the stability analysis for grid-connected MMC inverters is provided from the frequency domain. Positive and negative sequence impedance overlaps with the grid impedance, which predicts the sub-synchronous and super-synchronous oscillation of the PV medium-voltage DC power collection system under series compensation and verifies the consistency of frequency domain impedance and time domain waveform analysis. By controlling the parameter optimization, the sub-synchronous and super-synchronous oscillation phenomenon of the MMC under series compensation is effectively suppressed.
Fault Elimination Strategy of Symmetric Single-pole VSC-MTDC Based on DC Circuit Breaker
WANG Nannan, JIANG Chongxue, WANG Jiacheng, LU Yu, DONG Yunlong and TIAN Jie
2019, 43(6): 122-128.DOI: 10.7500/AEPS20180621011
[Abstract](175)[HTML](0)[PDF 1.42 M](90)
Abstract:
Aiming at the fast selective isolation problem of direct current(DC)line fault in DC circuit breaker application, the fault elimination strategy of symmetric single-pole voltage source converter based multi-terminal direct current(VSC-MTDC)transmission line is studied. The characteristics of single-pole-to-ground fault and pole-to-pole fault are analyzed, and the same cosine attenuation characteristics of the fault current changing rate in the early stage of single-pole-to-ground fault and pole-to-pole fault are obtained. A directional line selection strategy based on current changing rate, and the scheme for fault isolation and fault elimination using DC circuit breaker and reclosing strategy are designed respectively. The characteristic of fault current changing rate in the single-pole-to-ground fault and DC fault elimination strategy are verified based on PSCAD/EMTDC. Simulation results demonstrate the validity of the current changing rate characteristic and the effectiveness of the designed strategy for the elimination of the fault.
Reclosing Strategy for Hybrid DC Circuit Breakers
ZHANG Shengmei, AN Ting, PEI Xiangyu, YANG Jie, PANG Hui and ZHAO Chengyong
2019, 43(6): 129-136.DOI: 10.7500/AEPS20180528005
[Abstract](143)[HTML](0)[PDF 1.43 M](92)
Abstract:
Due to the use of overhead lines, the probability of temporary faults in the future voltage source converter(VSC)based DC grid will increase, and effective reclosing strategies must be adopted for the system recovery. To reduce the adverse impacts of protection misoperation, insulation failure, and even damage to power electronic devices caused by the synchronous operation of the hybrid DC circuit breaker transfer branch, a novel reclosing strategy based on the step-by-step operation of transfer branch is proposed. The results show that the abrupt change of voltage is largely reduced during the step-by-step operation of transfer branch, and the potential negative impacts could be eliminated thoroughly. Finally, the validity and feasibility of the novel reclosing strategy are verified in a four-terminal annular VSC based DC grid electromagnetic transient model, and the applicability of the two reclosing strategies is analyzed.
Distribution Network Fault Line Selection Based on Sequential Overlapping Derivative Transform Correlation Analysis
SHU Hongchun, LI Yifan, TIAN Xincui and FANG Yi
2019, 43(6): 137-144.DOI: 10.7500/AEPS20180812010
[Abstract](138)[HTML](0)[PDF 1.49 M](112)
Abstract:
In a resonant grounding system, the free-oscillation frequency of the cable-overhead line is typically between 3 00 and 3 000 Hz. In the initial stage of the fault, the transient information of the distribution network is rich, and the sequential overlapping derivative(SOD)transform can reflect the transient characteristic of the zero-sequence current. Therefore, the single-phase-to-ground fault line selection method based on SOD transform correlation analysis is proposed. And combined with the zero sequence voltage gradient summation as the starting criterion, the sensitivity and rapidity of the fault line selection are improved. The information of the transient zero-sequence current in the 0~2. 5 kHz band is extracted by wavelet transform and SOD transform is conducted. After the SOD transform, the similarity between the healthy lines is improved and the difference between the fault line and healthy lines is increased. Therefore, the correlation analysis of the results of the SOD transform is performed to form a fault line discrimination matrix. If the fault line discriminant matrix is all “1”, it is judged that the bus is faulty; otherwise, the line corresponding to“-1” is the fault line. The simulation shows that the method is almost independent of the initial phase angle, transition resistance and fault location, and the line selection result is accurate and reliable.
Neutral Point Intelligent Resistance Grounding Method Based on Single-phase Grounding Fault Zone of Distribution Network
LI Zhengyang, LI Jinglu, SU Sheng, ZHANG Chunhui, LIU Yang and YI Zhounan
2019, 43(6): 145-150.DOI: 10.7500/AEPS20180808003
[Abstract](156)[HTML](0)[PDF 1.62 M](86)
Abstract:
The distribution network using the small resistance grounding method has a high resistance dead zone, which has certain impact on personal safety, power supply reliability, and grid security. In order to solve the problem of small resistance grounding method, an intelligent resistance grounding method based on single-phase grounding fault zone is proposed. The method divides the faults according to the grid neutral point displacement voltage and fault line current change. In the high resistance fault zone, the double incremental start-up is adopted, and the fault lines are fast selected to remove faults. In the medium and low resistance fault zones, different delay processing methods are adopted to recover transient faults, improving the power supply reliability of distribution network and the personal safety and the power grid security. The developed device has been proved by experiment. It has a high resistance recognition processing capability of 5 000 Ω, which can recover the temporary fault of current amplitude of 65 A, and can accurately judge and remove the permanent fault. Compared with the small resistance grounding method, the intelligent resistance grounding method can effectively improve personal safety, grid security and power supply reliability.
Longitudinal Differential Protection of Transformer in Smart Substation Based on GOOSE Network
NI Chuankun, YU Tongwei, DENG Maojun, LI Baowei, HU Yebin and LI Xu
2019, 43(6): 151-155.DOI: 10.7500/AEPS20180528008
[Abstract](163)[HTML](0)[PDF 1.28 M](102)
Abstract:
For longitudinal differential protection of transformer, the starting current should avoid the influence of unbalanced current which is caused by the regulation of switch gear for on-load tap changer during the normal operation. When adjusting the wide range of switch gear, the sensitivity of differential protection would be influenced by high setting of the starting current. It is proposed that the gear position information could be obtained through the GOOSE network for the smart substation, and then the balance coefficient of the differential protection is adjusted automatically based on its actual gear position to eliminate the unbalanced current caused by gear position adjustment during the normal operation. Meanwhile, the tuning method of differential protection based on GOOSE network is proposed, which reduces the starting current and ratio restraint coefficient and improves the operation characteristics of differential protection. The simulation results show that the improved scheme can enhance the sensitivity and quickness of the differential protection of transformer.
Configuration Scheme of Emergency Load Shedding for HVDC Receiving-end Power Grid Based on Transient Low-frequency and High-voltage Features
CAO Yongji, ZHANG Hengxu, XIE Yuzheng, LI Changgang, FANG Yongjie, LI Zhaowei and DING Lijie
2019, 43(6): 156-162.DOI: 10.7500/AEPS20180404006
[Abstract](143)[HTML](0)[PDF 1.80 M](86)
Abstract:
In view of the under-frequency control problems of receiving-end power grid subjected to blocking faults of line-commutated converter-based high-voltage direct current(LCC-HVDC), a feature-driven scheme of emergency load shedding is proposed by taking into account the regular response pattern after the faults occur. The changing rule of frequency and voltage at the instant of LCC-HVDC blocking fault is derived, and the low-frequency and high-voltage feature caused by time-delay inter-tripping of reactive power compensation devices is analyzed. Moreover, the partial voltage characteristics are extracted by grey correlation analysis, and the initial changing rate of frequency is used to match the action scheme by k-nearest neighbor algorithm. On the basis of the traditional under-frequency load shedding scheme, an emergency load shedding stage is added to deal with the LCC-HVDC blocking fault, and the local-monitored low-frequency and high-voltage feature is used as the operation criterion, and is adopted to match the decision table in real time to cut off the load of fault areas. Finally, a provincial power grid is taken as a case to validate the effectiveness of the proposed scheme.
Egineering Application
Power Market Transaction Analysis of Index of Beijing Electric Power Exchange Center Under New Electricity Reform
SHI Lianjun, PANG Bo, LIU Dunnan, QIN Guangyu, LI Guodong and ZHANG Qian
2019, 43(6): 163-170.DOI: 10.7500/AEPS20180720012
[Abstract](315)[HTML](0)[PDF 1.33 M](220)
Abstract:
It is an important problem to effectively process and analyze power data with the increasingly active power trading markets across the country and the increasingly abundant types and quantities of power trading. Firstly, this paper analyzes all kinds of index preparation methods and their application in domestic and foreign markets, and presents the index of Beijing Electric Power Exchange Center(referred to as electric power index)which reflects the change of the electric power market transaction structure and quantity of electricity market participants to provide the reference and guidance to the market. Then, by referring to the guidance and instruction effect of Dow Jones theory and other market composite index theories in the securities market, the calculation and analysis method of the power market composite index is presented. It also explains how to analyze the characteristics of total electricity trading volume, seasonal fluctuation, regional difference and transaction type difference with the electric power index. The five factors influencing the electric power market composite index are investigated, including the total electricity consumption, market liberalization ratio, market trading price, trading varieties and market access area. Finally, the calculation formula of the electric power index is used to analyze the power market data from 2016 to 2017, and the results prove that the electric power index can accurately reflect the trade in the power exchange market.
Key Design Techniques of Low Voltage Ride-through Test System for Ultra-high Altitude Photovoltaic Power Station
WANG Deshun, WEI Haikun, YANG Bo, ZHAO Shanglin, YU Bin and HUA Guanghui
2019, 43(6): 171-176.DOI: 10.7500/AEPS20180321001
[Abstract](127)[HTML](0)[PDF 1.51 M](82)
Abstract:
The solar energy resources of high-altitude areas in Northwestern China are abundant and the large-scale grid-connected photovoltaic(PV)power station affects the safety and stability of the northwest power grid. The low voltage ride-through(LVRT)capability is an important indicator for the reliable access of PV power station to the northwest power grid. The LVRT test of PV power generation system in ultra-high altitude areas with an altitude over 4 000 meters needs to solve the problems of frequent operation overvoltage of test equipment and insulation coordination of plateau electrical equipment to prevent the occurrence of insulation discharge accidents. The insulation discharge problem of the test system depends not only on the high-frequency overvoltage generated by the switching reactor, but also on the optimal design of the equipment layout structure in a small space. An LVRT experimental system for PV power generation is proposed, and a method for the development of LVRT test equipment for PV power station in the ultra-high altitude regions is proposed. The factors that affect the transient overvoltage are analyzed theoretically, and the measures for the suppression of overvoltage in the test process are finally suggested. Through the finite element analysis method, the electric field strength inside the vehicle-mounted space is checked to ensure that no risk of insulation discharge occurs in the narrow space structure of the vehicle under the ultra-high altitude environment, and the electrical insulation safety of the equipment is ensured. The design scheme has been successfully applied to LVRT test system at an altitude of over 4 000 meters, and LVRT tests are carried out for several power stations.
Transformation Planning of Urban Distribution Network with Reliable Automatic Supply Transfer
LI Bin, SHU Qingchuan, LIANG Yufan and YI Yingqi
2019, 43(6): 177-183.DOI: 10.7500/AEPS20180319005
[Abstract](194)[HTML](0)[PDF 1.38 M](114)
Abstract:
The causes of the low load transfer rate of the ring network in the medium voltage distribution network are analyzed. It is proposed to optimize the partial load access points by changing the state of branch contact switches and reduce the load factors of the main feeders in the mesh-networking. The planning strategy can satisfy the conditions for safety verification at the minimal transformation cost. A feeder load balancing optimization model for radial distribution network based on Distflow is proposed to meet the feeder constraint of “N-1” load and network topology constraints. The second-order cone relaxation technique is applied to convexly relax the mixed integer nonconvex nonlinear programming so that the former condition can be transformed into a mixed integer second-order cone problem that can be efficiently solved. In order to verify the feasibility and effectiveness of this model, the model is tested by 68-node and 34-node distribution networks. The results show that the feeder can satisfy the requirements of automatic supply transfer only by reconstruction, and to some extent, can improve the economics of the distribution network operation.

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