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

Volume 43,Issue 2,2019 Table of Contents


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Special Report
Analysis on Blackout in Brazilian Power Grid on March 21, 2018 and Its Enlightenment to Power Grid in China
YI Jun, BU Guangquan, GUO Qiang, XI Gongwei, ZHANG Jianyun and TU Jingzhe
2019, 43(2): 1-6.DOI: 10.7500/AEPS20180812003
[Abstract](269)[HTML](0)[PDF 2.22 M](151)
On March 21, 2018, a large-area blackout occurred in Brazilian power grid because of a series of chain reactions caused by a circuit breaker overload protection. As sequence, the northern and northeastern power grids were disconnected from the main power grid in Brazil, 14 states in north and northeast area came to blackout, and 9 states in south, southeast and midwest area were also affected. The operation status of Brazilian power grid before the accident and the cause, process and recovery of the blackout are introduced. It is pointed out that the main causes of the accident are the lack of necessary stability analysis before the accident, the defects in security control, the misoperation of protection and the unreasonable configuration of the third line of defense. Combined with the actual situation of power grid in China, some recommendations are put forward to ensure the safe and stable operation of the power grid and to prevent blackouts. For example, attention should be paid to the setting and operation of protection and control devices.
Basic Research
Competitive Mechanism Design in Electricity Market Based on Fair Benefit Allocation
WANG Jianxiao, ZHONG Haiwang, XIA Qing, WANG Yang, LAI Xiaowen and GUO Xinzhi
2019, 43(2): 7-17.DOI: 10.7500/AEPS20180410009
[Abstract](190)[HTML](0)[PDF 1.42 M](132)
Promoting the electricity price reform, and constructing a “fair, open, organized, competitive and complete” electricity market are critical tasks confronted by the new-round electric power system reform of China. At present, the foreign electricity markets generally adopt locational marginal prices(LMPs)for electricity market clearing. However, the existing theory and practice demonstrate that LMPs cannot incentivize market participants to be truth-telling, and cannot solve the problem of information asymmetry. To incentivize market participants to truthfully bid and thereby achieve an optimal allocation for electrical resources, a competitive mechanism in electricity markets is proposed based on fair benefit allocation. Firstly, the phenomenon and reason why the LMP mechanism cannot elicit truthful information while leading to market efficiency loss are analyzed. Then based on Vickrey-Clarke-Groves(VCG)theory, a fair benefit allocation mechanism is proposed for day-ahead electricity markets, and it is proved that the proposed mechanism satisfies the properties of incentive compatibility, individual rationality and system cost minimization. The economic meaning why the proposed mechanism satisfies incentive compatibility is also explained. Case studies based on IEEE 30-bus and 118-bus systems validate the effectiveness of the proposed mechanism.
Bilateral Game Model of Power Supply and Demand Sides with Incomplete Information in Day-ahead Electricity Market
JIANG Wei, WU Jie, FENG Wei, DUAN Xiaofeng, TANG Haibo and WU Lei
2019, 43(2): 18-24.DOI: 10.7500/AEPS20180615003
[Abstract](188)[HTML](0)[PDF 1.48 M](107)
With the in-depth development of the direct power purchase by large consumers, the contradiction between the marketization of medium-long term bilateral transactions and the non-marketization of spot transactions has become increasingly prominent, thus the construction of the day-ahead electricity market is imminent. A bilateral game model is established with the incomplete information between power supply and demand sides in the day-ahead electricity market, which is aimed to provide a practical game scheme for both sides in the power transactions, so that both sides can obtain the greatest benefits in the power market. The model takes the direct power purchase price and amount as the key points of the game. For the part of the direct power purchase price, the generation cost factor is introduced and the co-integration theory is used to construct the relationship model between the direct power purchase price and the generation cost considering the error correction. The part of the direct electricity purchase amount is predicted by similar day method. Finally, the Nash equilibrium is used to find the solution of the bilateral game and the effectiveness of the proposed model is proved by an example.
Identification of Potential Harmful Behaviors in Electricity Market Based on Cloud Model and Fuzzy Petri Net
LIU Dunnan, ZHANG Qian, LI Xiaotong, GU Yugui and TAN Zhongfu
2019, 43(2): 25-33.DOI: 10.7500/AEPS20180405004
[Abstract](97)[HTML](0)[PDF 1.38 M](49)
To solve the problem of identification and control of potential harmful transactions in electricity market, a method for identifying potential harmful behaviors based on the cloud model and the fuzzy Petri net is proposed to realize real-time warning of potential hazards in the transaction process. The cloud model and the fuzzy Petri net are applied to pattern recognition, which effectively solves the problem that the potential hazard behavior is difficult to quantify, and overcomes the defects that the general recognition method is not easy to understand. Firstly, a general framework and procedure for identifying potential harmful behaviors is designed. Secondly, two methods of building feature cloud based on reverse cloud generator and expert description are described. Meanwhile, a fuzzy Petri net structure and recognition algorithm for potential harmful behaviors is designed. Finally, an example is made and analyzed by using the real transaction data of monthly auction market in Jiangxi Province, which shows the results given by the proposed method are highly consistent with the results obtained by artificial analysis and actual data.
Multi-objective Planning for Anti-disaster Backbone Grid Considering Economics and Network Frame Performance
HAN Chang, LIN Zhenzhi, YANG Li, CAI Jingdong, LYU Yunfeng and ZHANG Suming
2019, 43(2): 34-41.DOI: 10.7500/AEPS20180313002
[Abstract](105)[HTML](0)[PDF 2.47 M](56)
In order to enhance the power supply capability and disaster resistance ability of power systems under extreme natural disasters, a multi-objective planning method of anti-disaster backbone grid is proposed with the guarantee rate of the load requirements, security operation constraints of the power system and connectivity of the network topology satisfied. In the proposed strategy, a multi-objective planning model of anti-disaster backbone grid, in which the reinforce cost of differential planning, the efficiency of power resupply after a disaster and the ability of the backbone grid to resist the disaster are considered comprehensively, is constructed for maximizing economics, resilience and network survivability. The graph repair strategy is utilized in comprehensive learning particle swarm optimization algorithm, which increases the feasible solution space of the algorithm. Then, the mixed strategy Nash equilibrium, which can balance the benefit of each objective function, is adopted to extract the best compromise solution with the optimal equilibrium value from the Pareto fronts obtained by the algorithm. The feasibility of the proposed method is verified by the numerical results of a regional power grid in Guangdong Province.
Meteorological Disaster Prevention Method for Power Grid Based on Improved Stacked Denoising Auto-encoder Network
CONG Wei, HU Liangliang, SUN Shijun, HAN Hong, SUN Mengchen and WANG Anning
2019, 43(2): 42-49.DOI: 10.7500/AEPS20180302003
[Abstract](99)[HTML](0)[PDF 1.36 M](63)
The operation and maintenance data of power grid show that the main causes of the power grid fault have shifted from the level of manufacturing technology of electric equipment and the level of on-site operation and maintenance to natural weather factors such as thunder and lightning, mountain fire, gale and icy disaster. Disaster prevention and mitigation of power grid should also focus on meteorological disaster. Aiming at the characteristics and regularities of association between meteorological and power grid faults, a method of grid weather disaster mitigation based on improved stacked denoising auto-encoder(SDAE)network is proposed. Based on the meteorological historical data and grid operation and maintenance data, the synthetic minority over-sampling technique(SMOTE)is used to reduce the imbalance of the original data set. Auto-encoder network completes the extraction of meteorological information features and the establishment of the relationship meteorological information and grid faults through unsupervised self-learning and supervised fine-tuning, and improves the robustness of the network by incorporating sparse term restrictions and noise-enhanced coding. The case study shows that the proposed SMOTE-SDAE-based meteorological disaster mitigation method can establish the correlation mapping relationship between meteorological information and power grid fault accurately and completely, and can make accurate prediction for whether the given meteorological conditions will cause grid disaster accidents or not.
Small-signal Stability Assessment of Power System Based on Convolutional Neural Network
LI Yanglin, JIANG Quanyuan, YAN Rong and GENG Guangchao
2019, 43(2): 50-57.DOI: 10.7500/AEPS20171203004
[Abstract](126)[HTML](0)[PDF 1.35 M](61)
As the scale of power system increases, traditional numerical methods in eigenvalue computation for small-signal stability assessment are unable to meet the requirement of real-time analysis. Therefore, this paper proposes a small-signal stability assessment method based on deep-learning(convolutional neural network). This method takes the signals of wide-area measurement system as inputs of the model and generates critical eigenvalues as outputs. After the necessary preprocessing of the inputs and outputs, the mapping relationship between inputs and outputs can be established by deep neural network. Discrete cosine transformation and graphics processing unit parallelization techniques are employed to overcome the challenges from high dimension and slow training rate of large-scale system. Case study results indicate that the proposed method is able to accurately obtain the critical eigenvalues of the studied system after offline training using historic data, given no significant change in control parameters.
Security Correction Model of Power System with Novel Unified Power Flow Controller
ZHU Zirong, LI Qun, WEI Zhinong, ZHAO Jingbo, SUN Guoqiang and ZANG Haixiang
2019, 43(2): 58-66.DOI: 10.7500/AEPS20180508004
[Abstract](86)[HTML](0)[PDF 1.35 M](29)
New topology of unified power flow controller(UPFC)connected to different buses on shunt side and series side makes the traditional steady-state model of UPFC difficult to apply. Sensitivity-based security correction method ignores the effect of reactive power and may introduce new insecurity factors. Based on this, a steady-state UPFC model with high adaptability is proposed, along with an optimization model for power flow calculation with UPFC. Then, considering the influence of reactive power, a variable of 0-1 is introduced to transform the security correction problem into a multi-objective optimization problem with the objective of minimizing the number of adjusting devices and the amount of adjusting. Furthermore, the generator nodes and load nodes are distinguished by weights to reduce the occurrence of load shedding. Finally, the multi-objective optimization problem is transformed into a single-objective optimization problem by using the maximum method, which decreases the solving difficulty of the model. The test results of 116-bus equivalent system show that the proposed security correction model can eliminate the overload fault of the system by using the least adjusting equipment and adjusting amount, and the UPFC can improve the efficiency of the security correction.
Probabilistic Power Flow Calculation of Islanded Microgrid Based on Sparse Polynomial Chaos Expansion
HE Kun, XU Xiaoyuan, YAN Zheng, WANG Han and HONG Yuanrui
2019, 43(2): 67-75.DOI: 10.7500/AEPS20180809005
[Abstract](87)[HTML](0)[PDF 1.77 M](61)
Considering the effect of uncertainty of renewable energy source(RES)on the operation of microgrid, it is hard to comprehensively describe operation states and power flow distribution through the traditional deterministic power flow calculation. Based on the randomness and dependency of generators and loads in microgrid, this paper develops a probabilistic power flow model of islanded AC microgrid. The sparse polynomial chaos expansion method is adopted to obtain output response of islanded microgrid quickly and accurately, also it can improve the efficiency of probabilistic power flow calculation of microgrid with high-dimensional input variables. Finally, a 33-node islanded microgrid with several distributed generators is simulated, and the effectiveness and accuracy of the proposed method are verified by comparing with traditional methods.
Evaluation Method for Microgrid Cluster State Based on Fuzzy Least Squares Support Vector Machine
CHEN Weidong, LIANG Shuo, XIAO Yuanyuan and GUO Min
2019, 43(2): 76-82.DOI: 10.7500/AEPS20180311001
[Abstract](73)[HTML](0)[PDF 1.58 M](31)
Aiming at energy management system(EMS)and coordination control system(CCS)for adapting to flexible adjustment of microgrid cluster control strategy at variable operation states, a real-time operation state evaluation model of low-voltage microgrid cluster based on fuzzy least squares support vector machine(FLS-SVM)is proposed. With traditional power system operation state description method, the proposed model builds constraints in secure and normal operation of microgrid cluster and microgrid. Microgrid states are classified in view of multi-dimensional eigenvector including voltage deviation rate, energy storage state of charge, energy storage charge and discharge time, power generation and load. The real-time operation states of microgrids are evaluated with FLS-SVM, and then the operation states of microgrid cluster can be determined. Case study shows that the method can conduct the real-time evaluation within the sampling period of the system, and classify the operation states of microgrids accurately and effectively under the conditions of both off-grid and on-grid. It can provide the basis for microgrid cluster to quickly determine the operation state and flexibly adjust control strategy.
Scheme and Control Method of MMC Based Medium-voltage and High-power DC Distribution System
LI Hongliang, JIANG Jianguo, ZHOU Zhongzheng and ZHANG Dan
2019, 43(2): 83-88.DOI: 10.7500/AEPS20180102014
[Abstract](89)[HTML](0)[PDF 1.48 M](39)
A novel medium voltage DC power distribution scheme is proposed. In order to save the system volume, the structure of modular multilevel converter(MMC)and diode rectifier is used. Compared with the traditional 50 Hz control algorithm, the size of the converter can be greatly reduced by setting the output AC voltage and current base frequency to 1 kHz. As the fundamental frequency increases, the modulation algorithm must be simplified. An MMC square wave modulation strategy is proposed, which can save the controller resources compared with the traditional MMC modulation algorithm. In order to test the whole system rated operating conditions, a resistance microcirculation control scheme is proposed. The solution can achieve the internal power cycle, and the grid only provides the power consumption of the resistance and the system power dissipation, which can greatly reduce the pressure of the grid.
Analysis on Dynamic Performance of Droop Control for Multi-terminal VSC Based DC Distribution System
ZHAO Xueshen, PENG Ke, ZHANG Xinhui, XU Bingyin, CHEN Yu and ZHAO Yuehao
2019, 43(2): 89-96.DOI: 10.7500/AEPS20180211005
[Abstract](104)[HTML](0)[PDF 1.52 M](48)
Multi-terminal voltage source converter(VSC)based DC distribution system is better to meet the requirements of the development of future urban distribution system, while its flexible operation modes also pose new challenges to the control system. For different characteristics of droop control of converter, dynamic characteristics of the control system such as overshoot and damping ratio are analyzed theoretically. The influence of droop coefficient on the dynamic performance of converter power output is discussed, and small signal stability analysis is carried out. DIgSILENT simulation software is used to build a modified IEEE 33-node test system. The theoretical analysis and simulation result are consistent, and it shows that Idc-Udc and Q-Uac droop control strategies are superior to other droop strategies in terms of dynamic characteristics and high level of safety and stability, and it is more suitable to multi-terminal VSC based DC distribution system.
Classification Analysis Method for Electricity Consumption Behavior Based on Extreme Learning Machine Algorithm
LU Jun, CHEN Zhimin, GONG Gangjun, XU Zhiqiang and QI Bing
2019, 43(2): 97-104.DOI: 10.7500/AEPS20171214003
[Abstract](118)[HTML](0)[PDF 1.97 M](59)
Aiming at the classification problem of electricity consumption analysis of smart users under the background of big data, a classification method based on extreme learning machine(ELM)algorithm is proposed for electricity consumption behavior analysis. Firstly, based on the previous research of feature preference for electricity consumption behavior of smart users, the feature preference strategy is adopted to extract the best feature sets of the load curve, which helps to classify and analyze the data of electricity consumption for users. Then, the best feature sets are used as the input of ELM network. By comparing the accuracy of the training set and the test set with different hidden layer excitation functions and hidden layer node numbers, input parameters of ELM algorithm are selected, which are suitable for user's electricity consumption behavior analysis. Finally, the domestic and foreign electricity consumption data is taken as the data source to carry out the simulation experiment. Through the comparison and analysis with back propagation(BP)neural network, the results show that the analysis of electricity consumption behavior based on ELM algorithm improves the detection accuracy and reduces the algorithm operation time, which can better grasp the user load status and realize load balance of distribution network.
Application Research
Design and Application of Intelligent Power Control System for Integration of Renewable Energy
DUAN Hui, ZHU Yanfang, WANG Maxiang, XU Taishan, ZHAO Lihong and YANG Dachun
2019, 43(2): 105-111.DOI: 10.7500/AEPS20180213002
[Abstract](111)[HTML](0)[PDF 1.82 M](57)
Several existing problems in current power control of renewable energy are analyzed and the functional design and strategy of the intelligent control system for grid-connected power of renewable energy is introduced. The online sensitivity calculation method of the renewable energy station is proposed. Firstly, equivalent device in the state estimation system is confirmed according to grid-connected network of renewable energy power station. Based on real-time operation mode of the grid, the sensitivity of the equivalent device is calculated and then converted into the sensitivity of renewable energy station. The station/unit participating in the section control and the quantity of adjusted power is determined, and the problem of wind-coal coordinating control under the complex network structure is solved. When the renewable energy participates in peak regulation by tracking the negative spare capacity considering the regulation rate of thermal power unit and the area control error, the executed instructions would be adjusted in time once an exception occurs to ensure that automatic generation control(AGC)assessment indicators could meet the requirements. According to the power generation capacity, installed capacity and grid receiving space of the integrated renewable energy power station, the control sequence is determined and updated dynamically. The strategy can realize resource priority and fairness control among renewable energy stations and ensure the maximized consumption of renewable energy power. The operation result in Shanxi power grid shows that the intelligent control system can guarantee effectiveness of ensuring safe and stable operation of power grids, improving new energy consumption and promoting fair dispatch of new energy power stations.
Power Smoothing Control of Wind Turbine Generator via Coordinated Rotor Speed and Pitch Angle Regulation
TANG Xuesong, YIN Minghui, LI Dongyun, LIU Jiankun, ZHOU Lianjun and ZOU Yun
2019, 43(2): 112-120.DOI: 10.7500/AEPS20180319009
[Abstract](80)[HTML](0)[PDF 1.41 M](31)
Considering the fluctuation of wind power in seconds exerts an influence on the frequency stability of power grids, it is required to smooth the output power of wind turbine generators. Currently, the wind turbine-depended methods for smoothing wind power usually lead to frequent pitch adjustment, therefore, a power smoothing control method coordinating the rotor speed and pitch angle regulation is proposed. By separating the upward and downward regulation of pitch angle, the conventional constant-speed(upper speed limit)control is redesigned as the rotor speed range control so that the variable-speed operation at any pitch position is available and the kinetic energy buffer of wind rotor can be more adequately used to smooth wind power fluctuations. Correspondingly, while guaranteeing the smoothing effect, the proposed method can effectively reduce the frequency and amplitude of pitch actions, and alleviate the pitch servo fatigue and blade stress. Finally, the proposed method is verified by the wind turbine simulator based experiments.
Coordinated Control Strategy of AC/DC Hybrid Power Router Based on Voltage Stabilization by Energy Storage
LI Zhen, SHENG Wanxing, DUAN Qing, LI Penghua, WANG Jianhua and DU Songhuai
2019, 43(2): 121-129.DOI: 10.7500/AEPS20180504003
[Abstract](95)[HTML](0)[PDF 1.69 M](46)
AC/DC/AC converters, DC converters, energy storage and their converters are combined through a common DC bus to form the topology of power router which has two AC ports and three DC ports. Then, the typical operation modes are analyzed and the coordinated control strategy of AC/DC hybrid power router based on energy storage stabilizing voltage and virtual motor is proposed. Under the mode of single or double AC ports connecting to the grid, the power flow of two AC-DC converters are controlled by the power outer loop of virtual motor, while the DC voltage keeps steady due to energy storage. When both the AC ports are off-grid, not only keeps the DC voltage stable, but also supplies for AC and DC loads. The proposed strategy reduces the complexity of device control without mode switching. The stability of DC voltage is achieved in each operation mode, and the distributed generation is accommodated by local loads, and the constant and stable power supply for AC and DC load is ensured. Moreover, the flexible interconnection between the feeder lines of the distribution network is realized, and the power flows are transferred when the power grid fails, while the self-stable operation is realized when both the AC ports are off-grid, which effectively improves the power supply reliability of the low-voltage distribution network. Finally, the correctness and effectiveness of the proposed coordinated control strategy are verified by simulation and experiments.
Fringing Electric Field Suppression Method of Electric-field Coupled Power Transfer System with Four-plate Coupler
SU Yugang, FU Qunfeng, MA Junhao, QING Xiaodong and TANG Chunsen
2019, 43(2): 130-136.DOI: 10.7500/AEPS20180614003
[Abstract](65)[HTML](0)[PDF 1.60 M](21)
As the transmission power and distance of electric-field coupled power transfer(ECPT)systems increase, the plate voltage of the coupler will also increase, which brings the radiation of fringing electric field in the surrounding environment. This paper proposes a novel four-plate coupler to suppress the fringing electric field. Based on the modelling and analysis of the novel four-plate coupler, formulas of the voltage on four plates are derived by taking a double-sided LC-compensated ECPT system as an example. Moreover, the main affecting factors of the voltage on outer plates are analyzed, and a system parameter design method considering the transmission performances of the system is provided to suppress the fringing electric field. The validity of the proposed coupler and the design method has been confirmed by the simulation results.
Power Factor Correction Method Using Three-phase Single-switch Circuit for Wireless Power Transfer System
ZHOU Xiaomin, SUN Wen, GAO Dawei, LIN Shulin and HU Zhongyang
2019, 43(2): 137-142.DOI: 10.7500/AEPS20180503006
[Abstract](62)[HTML](0)[PDF 1.58 M](20)
An active power factor correction(APFC)control method using three-phase single-switch Boost circuit is proposed to reduce harmonic pollution to the power grid in the working process of wireless power transfer system. The effect of the coupling coefficient of coils on the control effect of APFC is studied by analyzing the working conditions of APFC circuit in the series-resonant wireless power transfer system. According to the output characteristics of three-phase single-switch Boost circuit and the impedance characteristics of series-resonant circuit, the working points of the system with variable coupling coefficient are corrected to achieve high power factor of input and high efficiency of output. The experimental results show that the proposed correction control strategy can reduce the distortion of input current and improve power factor and efficiency of wireless power transfer system with variable coupling coefficient.
Low Voltage Ride-through Control Strategy of Microgrid Inverter
FANG Zhixue, SU Jianhui, WANG Huafeng, SHI Yong and XU Huadian
2019, 43(2): 143-149.DOI: 10.7500/AEPS20180408004
[Abstract](86)[HTML](0)[PDF 1.52 M](51)
The microgrid inverter is generally controlled by droop controller or virtual synchronous generator, and the methods and characteristics of low voltage ride-through(LVRT)are different from inverters with PQ controller. The main problem of the LVRT strategy of the microgrid inverter is phase shift between the inverter voltage and the grid voltage during the fault, which would greatly affect the recovery speed of the grid-connected current. To solve the problems above, a strategy for memory retention of variables such as power angle during faults is proposed so that the variables before and after the fault are basically consistent to achieve rapid recovery of the system after the fault. The positive and negative sequence currents are separately controlled in the double synchronous rotating coordinate system and the forward feeding of the grid voltage is introduced to eliminate the negative sequence component during faults. Both the simulation and the experiment verify the correctness and effectiveness of the control strategy.
On-line Monitoring Technology of Inter-turn Short Circuit Fault of Dry-type Air-core Reactor
HUANG Xinbo, ZHOU Yan, ZHU Yongcan, CAO Wen, ZHANG Long and WU Hongxia
2019, 43(2): 150-155.DOI: 10.7500/AEPS20180113001
[Abstract](66)[HTML](0)[PDF 1.48 M](28)
The fault model of the inter-turn short circuit of the dry-type air-core reactor is firstly analyzed in this paper, by which an on-line monitoring method of the reactor inter-turn insulation fault based on the changed power angle is proposed. The accuracy of power angle measurement is vital for diagnosing the reactor inter-turn insulation fault. The influence of the frequency fluctuation and harmonic interference on measuring power angle is analyzed by comparing the errors of fast Fourier transformation(FFT), Hanning windowed interpolation FFT and fundamental harmonic separation algorithm improved by Hanning windowed interpolation. An on-line monitoring system of the reactor inter-turn insulation fault is also designed, which consists of the monitoring device, the intelligent electronic device(IED)of dry-type air-core reactor and the expert software. The experiment results show that the fundamental harmonic separation algorithm improved by Hanning windowed interpolation is superior to FFT and Hanning windowed interpolation FFT, and the inter-turn short circuit of the dry-type air-core reactor can be detected precisely by the on-line monitoring system.
Application of Information and Communication Technology
Lumped Parameter Cable Model for Low Voltage Power Line Communication
GUO Yihe, HUO Ran, LIU Xin, XIE Zhiyuan and QIU Juan
2019, 43(2): 156-161.DOI: 10.7500/AEPS20180608001
[Abstract](70)[HTML](0)[PDF 1.42 M](28)
In order to simulate the channel characteristics of actual low voltage power cable in laboratory environment, the lumped parameter cable model should be established under the power line communication band. A method is proposed to obtain the resistance and inductance by electromagnetic simulation and capacitance combined with the method of measuring and calculating distributed capacitances in open circuit tests. And on this basis, the transmission parameters of the cable are obtained. The transmission parameters are converted to Y parameters, and the π-type equivalent circuit is established. Based on the vector matching method, the passive equivalent circuits of each branch of the π-type equivalent circuit are solved, and the lumped parameter cable model is established. By comparing the calculation results of transmission and impedance characteristics with the distributed and lumped parameter models, the accuracy of lumped model is proved. The model can simulate actual cables of various lengths by circuit cascades.
Design and Implementation of Forward Isolation Device Based on Deep Packet Inspection and Security Enhancement
CAO Xiang, ZHANG Yang, SONG Linchuan, HU Shaoqian, TANG Zhenyu and ZHANG Chunhe
2019, 43(2): 162-167.DOI: 10.7500/AEPS20180316005
[Abstract](76)[HTML](0)[PDF 1.28 M](29)
In order to improve the security of power system communication network in the emerging network security environment and distribution network accessing environment, a forward isolation device based on deep packet inspection and security enhancement is proposed. Based on the principle and vulnerability analysis of the traditional forward isolation device, the field programmable gate array(FPGA)is adopted as isolation island to improve the transmission speed and reduce the error bit rate, the reverse penetrating threat is solved by the deep packet inspection technology, the security of human machine interface(HMI)management is improved by two factor authentication technology, the security of local management is improved by the encryption and authentication technology based on the state secret algorithm. Compared with the traditional forward isolation device, the performance and the security level of proposed device are both improved. Finally, the feasibility of the theory and the practicability of the technology are verified by project application.
Egineering Application
Mathematical Relation Between Network Topology and Power Supply Reliability
XU Yue and YU Tao
2019, 43(2): 168-175.DOI: 10.7500/AEPS20180625013
[Abstract](126)[HTML](0)[PDF 1.37 M](74)
Based on the concept of topology similarity, the theory that reliability of distribution network has a close relationship with topology is presented to avoid the topology being excluded in the reliability evaluation and rationalize the distribution network planning. First, the practical network is abstracted into a topology, and then this topology is presented by adjacency matrix with weight and failure degree matrix. Second, a similarity function is proposed based on vertex/edge sharing(VES). This paper also evaluates the reliability by clustering and extracts key factors to increase the reliability. Besides, branch permutation, network structure and the locations of distributed generators(DGs)are introduced as three indices to guide the distribution network planning. Detailed strategies are provided in the analysis of engineering project to verify the operability of the proposed method.
Voltage Balance Control of Valves in Hierarchical Connection Mode for Ximeng-Taizhou UHVDC System
GUO Hongguang, WU Yanwei, CHEN Dapeng, WANG Yatao, LI Nan and ZHOU Xiaofeng
2019, 43(2): 176-181.DOI: 10.7500/AEPS20180315007
[Abstract](81)[HTML](0)[PDF 1.30 M](61)
±800 kV ultra-high voltage direct current(UHVDC)transmission project from Ximeng to Taizhou is hierarchically connected to 1 000 kV and 500 kV AC grid in Taizhou converter station. As for this new circuit structure, it is very important how to ensure the DC voltage balance of two series valve groups connected to different voltage level AC grid in one pole for the safe and stable operation of HVDC transmission system. Combined with the UHVDC project from Ximeng to Taizhou, on the basis of the analysis of the control strategy of the DC transmission system, the voltage balance control of the series valve groups is studied, and the control strategy of voltage balance and the fault tolerance method of middle point divider are put forward. The RTDS modeling test verifies the correctness of the control strategy and achieves good application results in the HVDC project from Ximeng to Taizhou.
Key Technologies and Prospects for DC Power Grid Planning
LU Jingjing, HE Zhiyuan, ZHAO Chengyong, AN Ting, TANG Guangfu and PANG Hui
2019, 43(2): 182-191.DOI: 10.7500/AEPS20180828005
[Abstract](197)[HTML](0)[PDF 1.54 M](103)
The vigorous development of new energy has made fundamental changes in the mode of supply and usage of traditional energy. Meanwhile, the new situation in the coexistence of power generation of large coal power, hydropower, photovoltaic and wind energy has brought great challenges and profound innovations to the traditional power transmission technology. The DC power grid based on traditional line commutated converter(LCC)and flexible voltage source converter(VSC)technology is investigated, and the research trends of DC power grid planning are reviewed. Firstly, the features and advantages of DC power grid are analyzed, and the framework of DC power grid planning is put forward and elaborated in detail. Then, the research ideas based on two application scenarios for DC grid planning are proposed, including the access of new energy to grid, multi-infeed and multi-terminal DC network. The multi-power electronic equipment co-optimization DC planning is also discussed. Finally, the preliminary planning of the demonstration project of the Zhangbei ±500 kV flexible DC power grid is briefly analyzed. And the key issues and prospects for researches of DC power grid planning in the future are provided.

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