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

Volume 38,Issue 24,2014 Table of Contents

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Global Outlook
A Review of CIGRE’ 2014 on New Development of Rotating Electric Machines
SUN Yutian, LUAN Qingwei
2014, 38(24): 1-4.DOI: 10.7500/AEPS20141022001
[Abstract](2582)[PDF 1.08 M](1338)
Working group subjects and academic papers for study committee of rotating electrical machines of CIGRE’2014 are introduced. The scope involves technology progress of turbogenerators, hydrogenerators, wind-driven generators and large motors in the areas of CIGRE Study Committee A1: rotating electrical machines (CIGRE SC A1).
Automation of Green Power
Interval Linear Programming Method for Day-ahead Optimal Economic Dispatching of Microgrid Considering Uncertainty
WANG Shouxiang, WANG Dong, HAN Liang
2014, 38(24): 5-11.DOI: 10.7500/AEPS20131212010
[Abstract](2415)[PDF 1.27 M](1517)
The renewable energy power and load power in a microgrid both have uncertainty characteristics, the effects of which are worth careful consideration in the optimal economic dispatching of the microgrid. In order to characterize these uncertainties in the microgrid, the randomness of the wind speed and light intensity is described by the interval, and combined with the interval description of load uncertainty, a microgrid economical optimization model based on interval linear programming (ILP) is proposed. Then by referring to the time-of-use pricing, the issue of power exchange with an external grid is considered. The CPLEX optimization software combined with the C++ programming is applied to the above issue. Finally, with the influence analysis of energy storage on the economical operation of the system as an example, the impact of uncertainty of renewable energy power and load power on the optimization result is discussed. The results have verified the robustness of the proposed method and model, and shown their effectiveness in dealing with uncertainty optimization.
Energy Storage Capacity Optimization for Wind Farms Considering Optimal Expected Output and SOC
ZHANG Feng, LIANG Jun, ZHANG Li, HAN Xueshan, WANG Hongtao, WEI Zhongkang
2014, 38(24): 12-19.DOI: 10.7500/AEPS20131029002
[Abstract](2445)[PDF 1.02 M](1583)
The cost of energy storage allocation contradicts the smoothing effect of power fluctuation, while energy storage capacity optimization is a feasible way to solve this problem. Firstly, by taking the minimum target value offset variance as the optimal object, the optimal expected output is calculated to eliminate the subjectivity during the determination of output target value of power fluctuation smoothing. Such a line of thought is regarded as the theoretical basis of energy storage capacity optimization. Secondly, considering the parameter of state of charge (SOC) and based on the fuzzy control theory, the charge and discharge power is adjusted timely according to the SOC and the charge-discharge state. Then the charge and discharge strategy for the energy storage system (ESS) is devised while excessive charge or discharge is obviously restrained. Finally, the optimization mathematical model is developed to minimize the sum of penalty cost and running cost, while the energy storage capacity optimization balancing the dispatching decision demand, ESS service life and operating economy are realized. The improved particle swarm optimization (PSO) algorithm is adopted for optimization calculation, with the effectiveness of the method shown by actual wind farm data.
A Droop Control Strategy Based on Drooping Coefficient with Adaptively Changing Steps
ZHANG Dong, ZHUO Fang, SHI Hongtao, GENG Zhiqing, ZHAI Hao
2014, 38(24): 20-25.DOI: 10.7500/AEPS20131231006
[Abstract](2112)[PDF 1.69 M](1659)
Owing to the randomness of the output power in a distributed generation system, the voltage of the bus in an islanding microgrid will fluctuate to an extent that will cause detrimental effects on the payloads connected to that microgrid. A droop control strategy based on drooping coefficient with adaptively changing steps is proposed to suppress the voltage fluctuation of the microgrid bus bar induced by output power swings of a distributed generation system. Simulations and experiments are conducted to validate the proposed algorithm. Results show that a microgrid connected to a distributed generation system is able to maintain the stability of its voltage of the bus by adopting the algorithm based on droop coefficient with adaptively changing steps.
Basic Research
A Market Mechanism for Participation of Electric Vehicles and Dispatchable Loads in Distribution System Congestion Management
LIU Weijia, WU Qiuwei, WEN Fushuan, XUE Yusheng
2014, 38(24): 26-33.DOI: 10.7500/AEPS20131104003
[Abstract](3946)[PDF 1.23 M](1654)
In the electricity market environment, a reasonable market mechanism is demanding for guiding the behaviors of interruptible loads and flexible loads such as the charging loads of electric vehicles (EVs) to alleviate peak demands and system congestion. First, according to the response characteristics of different kinds of loads, the temperature controlled domestic loads are chosen as controllable loads. Besides, the EV charging demand and discharging power with the vehicle to grid (V2G) mode are considered as flexible loads. The demand response models of the controllable/EV demands are presented based on their thermal models/charging and discharging characteristics. Then, given the economic rationality of the retail agents (RAs) for interruptible and EV loads and the demand response models, RAs will formulate the initial bidding plans for the next trading day; the initial bidding plans will be verified by the distribution system operator, and an optimal power flow model will be employed to calculate congestion fees if applicable. Afterwards, the RAs will employ these congestion fees to reschedule and coordinate the domestic controllable loads and EV charging/discharging loads, given that the customers’ needs and constraints are properly respected. With the proposed market mechanism, the peak demands can be alleviated and distribution system congestion avoided to a great extent. Finally, the developed market mechanism, mathematical models and congestion management strategy are demonstrated through the modified IEEE 33-bus distribution system.
A Development Pattern Argumentation Method for Battery Electric Vehicles in Cities
LIU Wenxia, ZHANG Leilei, LIU Zongqi, HE Jian
2014, 38(24): 34-40.DOI: 10.7500/AEPS20130805001
[Abstract](2950)[PDF 954.35 K](1363)
In recent years, it has become an inevitable trend to popularize electric vehicles (EV). And the factors affecting and restricting large-scale development of EVs are battery energy storage, economic costs and public infrastructure facilities. At present, EVs have ordinarily three kinds of charging mode options: plug-in charging, battery replacement and fast charging, of which fast charging is but an emergency measure for the first two. Choosing different charging modes will have different influence on the economic costs, charging infrastructure and the grid. Therefore, to determine EV development and operating modes applicable to different cities and areas, for the sake of evaluation and selection of suitable charging modes, and based on practical application and theoretical optimization, a comprehensive analysis is made and an adaptive multiple parameter evaluation method proposed, to comprehensively analyze the first two charging modes with respect to social benefits, economic benefits, technical and safety, and grid influence. Technical support is provided to each city and area to explore an appropriate EV development mode. This method is verified toward the end of the article.
Cost-benefit Model and Its Sensitivity Analysis for Battery Charging and Swapping Station for Electric Vehicles
DAI Qian, DUAN Shanxu, CAI Tao, CHEN Tianjin, HUANG Ling
2014, 38(24): 41-47.DOI: 10.7500/AEPS20131225004
[Abstract](2839)[PDF 1.02 M](2427)
Battery charging and swapping stations (BCSSs) for electric vehicles has become an important infrastructure contributing to the development and spread of electric vehicles in China. The cost-benefit model of BCSS is crucial for its commercialization. In this paper, the battery lease mode is chosen as the operation mode of the BCSS. On the grounds of the chosen mode, the cost-benefit model of the BCSS based on the time-varying economic assessment index including net present value is built that considers the whole capital costs, the maintenance and operation fees, employee wages and service returns from swap and charging. Finally, with a BCSS based on leased mode in China as an example, the whole life cycle cost-benefit model is presented and the key elements affecting the station’s revenue are found through a sensitivity analysis. The sequence of sensitivity elements is as follows: the battery swapping price, lease rental of batteries, electricity price, and so on. The model of BCSS and its sensitivity analysis has provided a basis for cost-benefit assessment and decision marking for commercial operation of BCSS of electric vehicles.
Reactive Voltage Control of Bidirectional-interaction Coordination Between Provincial and District Power Networks with Wind Power Integration
WANG Bin, GUO Qinglai, LI Haifeng, SUN Hongbin, TANG Lei, ZHANG Boming
2014, 38(24): 48-55.DOI: 10.7500/AEPS20140503003
[Abstract](2092)[PDF 1.51 M](1329)
An agile and coordinated voltage control method is proposed to deal with the power system reactive power and voltage operation with large scale wind power integration. In the provincial control center, the agile voltage control method with the wind power volatility and the power system N-1 security constraints taken into account is proposed. With this method, by means of the adaptive adjustment of the control period and control model, the wind farm reactive ability will be fully tapped to suppress the influence of wind fluctuations on the bus voltage while sufficient dynamic reactive power regulation margin of traditional generators will be retained. Between provincial and prefectural control centers, the bidirectional interaction based voltage control method is presented to support the voltage at the terminal power network while bypassing the unnecessary discrete device action on the prefectural grid. By coordinated voltage control among the wind farms and substations in the provincial power system, the control abilities of its own wind farms will be made full use of, there will be less capacitor and reactor action times in its own substations and unnecessary reactive power flow. By the bidirectional interaction between provincial and prefectural control centers, the distributed adjustment resources can well be used to support the voltage at the terminal power network and increase the safety and economy of overall operation of the power system. The wind automatic voltage control system is currently in real-time operation in Jiangsu power system.
Application Research
Improved Fast Model of the Modular Multilevel Converter
TANG Geng, XU Zheng, LIU Sheng
2014, 38(24): 56-61.DOI: 10.7500/AEPS20131204005
[Abstract](2458)[PDF 1.23 M](1245)
This paper proposes an improved fast model for the modular multilevel converter (MMC) which, compared with existing fast models, is capable of accurately simulating the converter arm with DC converter blocked. The proposed fast model replaces the converter arm with an equivalent sub-module. Under un-blocked simulation, the converter arm can be treated as a Thevenin’s equivalent circuit, which is similar to the existing fast model. While under the DC converter blocked condition, the converter arm is simplified as an uncontrollable sub-module with lumped parameters. Two-stage start-up simulation and DC line fault simulation are carried out to verify the accuracy of the improved fast model. By comparison, the existing fast model has appreciable computational errors under DC blocked simulation because of the negligence of interpolation of diodes. However, the proposed improved fast model, which takes the interpolation of diodes into account, has very good accuracy under DC blocked simulation.
Arm Current Analysis of Modular Multilevel Converter and Its Circulating Current Suppressing Method
LI Guoqing, XIN Yechun, WU Xueguang
2014, 38(24): 62-67.DOI: 10.7500/AEPS20140319011
[Abstract](2018)[PDF 1.11 M](1582)
In order to prevent the modular multilevel converter (MMC) internal circulation, an analysis is made of the voltage fluctuation and circulation generating mechanism of the MMC bridge arm, and a kind of compensation control method for circulation inhibition is proposed. When the MMC power exchange is in progress, the effect of bridge arm current causes the periodic change in the submodule capacitor voltage. It has found that submodule capacitor voltage contains DC component and AC component using the average value analysis method. For converter voltage modulation using the nearest level modulation method, it has been found that, as the submodule capacitor voltage contains DC component and fundamental component deviation, there exists fundamental frequency deviation and double frequency component between bridge arm voltage and the expected value, resulting in the circulation. By compensating for the bridge arm voltage and expected value deviation, it will be possible to eliminate bridge arm voltage deviation, thereby suppressing the circulation among the converter bridge arms. The 11-level MMC DC transmission system is set up in PSCAD/EMTDC, with the effectiveness of the method proposed verified by simulation results.
A DC-side Active Charging Strategy for Modular Multilevel Converters
DONG Yunlong, TIAN Jie, HUANG Xiaoming, ZHONG Xiaobo, WANG Nannan, LIU Mingkang
2014, 38(24): 68-72.DOI: 10.7500/AEPS20140401004
[Abstract](2881)[PDF 1.11 M](1638)
In the voltage source converter based high voltage direct current (VSC-HVDC) transmission project, the converter valve of the passive terminal must be pre-charged via the active terminal, while the sub-modules can only be charged to half the rated voltage at most. A very large DC current will be generated if the converter is deblocked in normal logic. So the sub-modules must be charged to the rated voltage by an active charging strategy. According to the characteristics of DC-side uncontrolled charge and normal operations of the modular multilevel converter (MMC), a DC-side active charging strategy for progressively decreasing the operated sub-modules is designed. The strategy makes possible the smooth transition of the converter valve of the passive terminal from the uncontrolled charging state to the normal deblocked operation state. Besides, the characteristics of the bridge arm current in the DC-side active charging process are analyzed. Finally, simulation results and the project application have verified the strategy designed.
PRIME-based Method for Constructing Power-line Carrier Communication Networks in Low-voltage Distribution Networks
LI Teng, ZHU Jinda, JIANG Yuanyuan, PAN Zhengcheng, SUN Nan
2014, 38(24): 73-79.DOI: 10.7500/AEPS20140520014
[Abstract](1802)[PDF 974.99 K](1217)
The topology and characteristics of power-line carrier communication networks in low-voltage distribution networks are described. In view of the frame structure and type of the media access control (MAC) layer in the standards of powerline intelligent metering evolution (PRIME), the initialization algorithm and the network maintenance and routing reconstruction algorithm for constructing power-line carrier communication networks in PRIME are analyzed and summarized. By using the power-line carrier chip ST7590T and applying the PRIME standard protocol, a test environment with 96 nodes in field has been built for analyzing the initialization and reconstruction process of the networking method. For situations that may appear on the spot, the network flexibility, invulnerability and field applicability of the networking method have been verified.
Faulty Feeder Identification Based on Combined Transient and Power-frequency Components in Resonant Grounded Systems
XUE Yongduan, ZHANG Qiufeng, YAN Tingchun, XU Bingyin
2014, 38(24): 80-85.DOI: 10.7500/AEPS20131210015
[Abstract](2237)[PDF 961.82 K](1085)
The power-frequency component is no longer suitable for faulty feeder identification in a resonant grounded system. Influenced by the incorrect polarity connection of voltage transformer and current transformer, faulty feeder is apt to result using feeder identification based on transient current polarity or transient reactive power direction comparison. The distribution differences between transient and power-frequency current as well as transient and power-frequency reactive power for single-phase earth fault in the compensated system are analyzed, based on which, two faulty feeder identification methods based on combined transient and power frequency components are proposed. A faulty feeder is one with a polarity different from that of both the transient zero sequence current and power frequency zero sequence current of healthful feeders, or, a feeder is identified as a faulty one if its transient reactive power and power-frequency reactive power have different directions. The proposed methods have fairly good faulty feeder identification reliability for their ability of avoiding incorrect polarity connection of voltage transformer and current transformer. The feasibility of the new methods is verified by both digital simulation and field test data.
Countermeasures to Overcome Outflow Current for Bus Differential Protection
DU Dingxiang, ZHOU Zexin, WANG Xingguo, AI Shuyun, ZHOU Chunxia, LI Zhongqing
2014, 38(24): 86-90.DOI: 10.7500/AEPS20131120006
[Abstract](1732)[PDF 929.48 K](1126)
The outflow current during an internal fault on the bus will decrease the sensitivity of the relays for the overall differential element and even lead to operation refusal or trip time delay for the total protection. To solve the problem, improved criteria and a concrete implementing scheme are put forward. First, the influence of outflow current on conventional bus protection for double-bus and double-bus double-segment connection modes is analyzed. Then, the restraint current calculation method of the new ratio differential criterion is proposed and the characteristics of the new algorithm during internal and external faults are analyzed. Finally, the implementation scheme matching small range differential relay is put forward and the validity of scheme is verified by dynamic simulation test.
Ratio-restraining Differential Protection of Lines Based on Charge
KONG Linghao, JIAO Yanjun, DAI Zhihui, CHONG Zhiqiang
2014, 38(24): 91-95.DOI: 10.7500/AEPS20130726001
[Abstract](2083)[PDF 914.87 K](1310)
The ideas of differential charge and restraining charge are proposed along with an analysis of their relationship. Based on the ideas, a ratio-restraining differential protection criterion for lines and its setting rules are presented. The protection criterion is able to identify internal and external faults based on full wave current. The idea of avoiding the influence of anti-TA saturation and capacitive current is enumerated. Finally, simulation results show that the proposed protection criterion is capable of quick and accurate identification of an internal fault within 5~10 ms and reliable lockout protection during an external fault.
Rapid Diagnostic Method of Stator Ground Fault Caused by a Faulty Terminal Capacitor
TU Xiaotao, ZHANG Zhengping, HU Wei
2014, 38(24): 96-101.DOI: 10.7500/AEPS20140418012
[Abstract](1891)[PDF 950.42 K](1041)
It is difficult to diagnose the stator ground fault caused by a faulty terminal capacitor with the help of detecting insulation resistance. The corresponding mechanism is analyzed first based on the equivalent circuit of stator ground fault. Three-phase reference composed of stator voltages is adopted to make a comparative analysis on the phase characteristics of zero sequence voltage, which can be used to discriminate the stator ground fault caused by a faulty terminal capacitor or grounding transient resistance. And a practical method is proposed based on the foregoing characteristics. In this approach, the position of zero sequence voltage in the three-phase reference can be judged by voltage waveforms from the wave-recording device. Furthermore, the winding capacitance to ground and grounding resistance of the neutral point should be utilized to realize rapid diagnosis. Finally, the effectiveness of the proposed approach is verified through a relevant fault example.
Design of Substation-area Protection and Control Equipment Based on Backboard Bus
DING Yi, CHEN Fufeng, ZHANG Yun, YU Huawu, LAN Jinbo
2014, 38(24): 102-107.DOI: 10.7500/AEPS20130920001
[Abstract](1986)[PDF 1.00 M](1226)
A backboard bus based design scheme for substation-area protection and control equipment used in smart substations is proposed. A multiple master communication backboard bus is designed based on multi-point low voltage differential signaling (M-LVDS). The cooperation model is described according to resource configuration and logic diagram division. With backboard bus as the core, a multi-level dataset interaction and control model is developed between the virtual logic bus, backboard bus, process bus and wide area communication network. Several topics are discussed, such as the principle of backboard, realization and function division of logic diagram, realization of multi-level data exchange. The design scheme proposed is applied in substation-area protection and control equipment for a 110 kV smart substation for function transfer, redundancy protection, concentrated backup protection, safety automatic control, etc. Site operation has proved its effectiveness and practicality.
Egineering Application
Accommodating Capacity and Mode of Distributed Generation Under Harmonic Constraint in Active Distribution Networks
ZHONG Qing, GAO Xinhua, YU Nanhua, LI Lanfang, WANG Ling
2014, 38(24): 108-113.DOI: 10.7500/AEPS20131214002
[Abstract](2222)[PDF 945.15 K](1397)
This paper firstly analyzes the harmonic emission characteristics of a single distributed generation (DG) device and calculates the maximum capacity of DG under harmonic emission constraint. Based on the vector summation theory, the maximum capacity of multiple DGs accessed to a common point is also calculated. Finally, a case study is carried out to analyze the harmonic characterization in the active distribution network with multiple points of common coupling. A case study is designed for three classic power accommodating modes: point accommodating, feeder accommodating and area accommodating. Three-dimensional parameters including penetration, distribution and dispersion are defined to describe the status of DGs accessed to the active distribution network. According to the study, a conclusion can be drawn that the harmonics in the active distribution network is closely related to the three-dimensional parameters. Full consideration should be given to prevent and solve the harmonic problem during the planning and operation stage of the active distribution network.
Fault Location for Electric Power Communication Network Based on Intersection Operation and Combined Fuzzy Condition
WANG Xiang, DAI Fei, GAO Weizhong, CHAO Yujian, WU Bo, HU Hongyan
2014, 38(24): 114-118.DOI: 10.7500/AEPS20141125001
[Abstract](1611)[PDF 939.97 K](1170)
In view of the characteristics of large amount and great scale, complex structure and increasingly high fault incidence of modern power communication network, a fault location intelligence analysis method for the electric power communication network is proposed. The adoption of intersection operation for the fault multi-level location and the combined fuzzy logic operation to locate the faults in the carriers for the information signal is a good choice. By using this method, the fault can be accurately and quickly located on the position, physical device, logical circuit, and communication transactions, improving the operation maintenance and management level of the electric power communication network.

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