An optimization algorithm based on Petri net topology for PMU placement in power system. A new optimization algorithm for PMU placement is introduced in this article. The net-cover function is built based on rules that associated nodes are observable with the choice of PMU location is considered. Then referring to the information of connection nodes, the whole power network is analyzed with improved Petri Net. And the optimized network cover is achieved. The complex power network is divided into several parts, the change enable array is renewed, and the marking operator is used. The analysis scale is reduced and the inference process is simplified. Finally, from the testing results of methods with the actual data of the real power network, the method proposed is relatively accurate and the processes of calculations are feasible and convenient. 9 Refs. In Chinese.
Key Words: improved Petri net; topology analysis; PMU placement
LAN Hua (School of Electrical Engineering, Northeast China Dianli University, Jilin 132012, China), WANG Yun-ran, QU Jing, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 1—5.

HF Circuit model of generator stator bar based on PEEC. Modeling an accurate circuit of generator stator windings is significant for researching Partial Discharge (PD) propagation in stator windings and the characteristics of PD. There are mainly three faults about the stator windings circuit model based on the multi-conductor transmission line theory: firstly, the signal propagating in stator windings is not strictly a TEM mode; secondly, it is difficult to set up a reasonable end-windings circuit model with transmission line theory; and finally it is impossible to establish a complex coupling circuit model of the stator windings and the PD sensors. This paper develops a new HF circuit model of single stator bar and a coupling circuit model of two coupled bars on the basis of Partial Element Equivalent Circuit (PEEC) method, which has an advantage over the multi-conductor transmission line theory in modeling circuit of generator stator windings. The partial inductance matrices and partial capacitance matrices in the model are calculated by using PEEC theory and FastModel – a special calculating software developed by MIT. The consistency between the experiment results and the simulation results shows that the PEEC model and the parameters are feasible and accurate enough within the frequency range under test. 10 Refs. In Chinese.
Key Words: partial discharge; stator winding; Partial Element Equivalent Circuit (PEEC); propagation model; partial inductance; partial capacitance
WEI Yan-fei (Dept. of Elec. Eng., Tsinghua University, Beijing 100084, China), CAO Hai-xiang, SUN Xu-dong, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 6—10.

Rotor current control of doubly-fed induction generator based on active-disturbances-rejection controller. Doubly-fed induction generator has received much attention as one of preferred technology for wind power generation. As its increasing capability in the whole power system, more and more scientific researchers become interested in the stability of doubly-fed induction generator. This paper analyses the 5th model of DFIG, discusses its conventional controller-PID controller and points out the disadvantages. Then a new rotor current controller based on active-disturbance-rejection control theory is proposed to improve the dynamic response of the system under grid disturbances. Besides, this paper carries out simulation of the controller under normal condition and grid disturbances. The results show that the proposed controller can not only tune system power output precisely in normal condition but also ensure prominent reduction of rotor current ripple in order not to be disconnected. The results also prove that the approach has lots of advantages in response speed, control accuracy and adaptability. Moreover, the controller takes on good dynamic performances. 6 Refs. In Chinese.
Key Words: doubly-fed induction generator; rotor current; grid disturbances; active-disturbances-rejection controller
XIA Chang-liang (School of Elec. Eng. & Automation, Tianjin University, Tianjin 300072, China), SONG Zhan-feng // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 11—14.

Research on interaction between operation of high voltage circuit breaker and chaotic oscillation
LIU Dong-hui1, XIA Cheng-quan3, SHI Ke-qin2, SHAN She-wu1
(1. Shanxi Electric Power Dispatching Center, Xi’an 710048, China; 2. Northwest Electric Power Dispatching and Communication Center, Xi’an 710004, China; 3. Xi’an Jiaotong University, Xi’an 710049, China)
Abstract: The interaction between the operation of vacuum interrupter and the chaotic oscillation is researched through a simplified model in the paper. According to the bifurcation theory of the system, the dynamic process of system is researched with different parameters while the vacuum circuit breaker is opening, and the operation situation of vacuum interrupter is also researched in chaotic regime.
Key words: vacuum circuit breaker; chaotic oscillation; Lyapunov exponents

Small-signal stability analysis and coordinated control based on subspace algorithm. In this paper a subspace algorithm is applied to identify the MIMO model of power systems from measured input-output data and then to design expected controllers. The identified model is proved to be valid for extracting electromechanical eigenvalues on line through comparing estimated results with their theoretical values, which are acquired from linear model of simulated system. Each generator is excited by pseudorandom binary signal at the AVR’s reference, and its response such as speed, voltage and active power are sampled by phasor measurement unit. The identified low-order MIMO model is applied to design decentralized and coordinated excitation laws, which are decided by optimal feedback coefficients and derived from the solution of a Levine-Athans equation. At last, an eight-machine test system is studied, satisfied model cross validation illustrates the identification is successful. Estimated eigenvalue is very similar to their actual values. Also, the excitation laws based on identified model have ensured good dynamic characteristics. 12 Refs. In Chinese.
Key Words: subspace algorithm; system identification; small-signal stability; power system; excitation control
HAO Zheng-hang (Elec. Eng. College, Guizhou University, Guiyang 550003, China), CHEN Zhuo, LI Shao-bo, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 20—23.

Characteristics of common-mode conducted current in electric vehicle. Common-mode current conducted through chassis and cables is the main source of electromagnetic interference (EMI) in an electric vehicle. In this paper, equivalent circuit models of the common-mode current for its generation and propagation are presented, showing that the common-mode current is determined by the impedance between cables and chassis. The impedance is further analyzed on the basis of transmission line model with the results of the characteristics of capacitive, serial resonance, inductive and parallel resonance in turn. It causes different distribution of common-mode current with different frequency along the cable. The analytical result is consistent with the measurement of common-mode current along the cable. Furthermore, to reduce the common-mode current, desirable position and value of common-mode inductance are proposed. 8 Refs. In Chinese.
Key Words: electric vehicle; common-mode current; impedance between cables and chassis; conduct characteristics
HUANG Yong (State Key Lab. of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China), ZENG Fan, CHEN Quan-shi, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 24—28.

Shimming method for permanent magnet of open-type low-field MRI. In the process of producing a permanent magnet, shimming is one of the key techniques for improving the efficiency and quality. At present, for the domestic manufacturers, the shimming methods of the open type low-field MRI lack the support of an integral theory. For this reason, the spherical harmonic function is introduced in analyzing the magnetic field and establishing the project both for active and passive shimming. The low-order terms of the spherical harmonic expansion can be easily shimmed by using the shim coil system. However, when the requirements exceed the capabilities of the corresponding active shim device, and when the high-order distortions are necessarily to be cancelled, passive shimming is applicable. In the experiment, the shim coils for the　 term that require heavy current can not be realized. Therefore, this paper adopts permanent magnetic material instead of shim coils, achieving good compensation for the magnetic field. 11 Refs. In Chinese.
Key Words: open-type low-field MRI; permanent magnet; shimming method; permanent magnetic material
ZHAO Wei (School of Communication Science & Technology, Beijing Institute of Technology, Beijing 100081, China), LIU Zhi-wen, LIU Yong, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 29—32.

New evaluation system for energy savings based on efficiency and loss ratio
ZHU Yong-qiang, YIN Zhong-dong
(Key Lab. of Power System Protection and Dynamic Security Monitoring and Control, Ministry of Education; School of Elec. Power and Elec. Eng., North China Electric Power University, Beijing 102206, China)
Abstract: On the basis of overview on present evaluation methods of energy saving effect, a new evaluation system is established in this paper. The concepts of effective and ineffective energy which is also called energy losses are proposed and introduced in detail classifications according to their nature and causes. The definitions of efficiency of energy utilizing and loss ratio are provided. The efficiency of energy utilizing is referred to as the proportion of effective energy in the total energy. The loss ratio is referred to as the ratio between loss and effective energy. The relationship between the two new indexes is demonstrated too. A new evaluation system for the effect of energy saving is established on the basis of those indexes proposed in this paper. The evaluation system based on efficiency and loss ratio is convenient for comparison among different energy-saving measures and is helpful to take proper measures to save energy.
Key words: energy saving; efficiency; loss ratio; evaluation

Economic dispatch based on particle swarm optimization of stochastic simulation in wind power integrated system. Wind power can not be forecasted because of its randomness. So the economic dispatch in wind power integrated system is not a traditional determinate question. The solution which is economic and reliable is difficult to attain by traditional ways. This paper put forward a mathematical model of economic dispatch in wind power integrated system based chance constrained programming (CCP) and describes the related constrained conditions in probability form. These include ramp constraints of the generating units, output restricted zone, line transmission capacity, reserved capacity constraints, the balance of load and so on. The question is solved by particle swarm optimization (PSO) based stochastic simulation. The optimization algorithm is proved effective by IEEE30 testing. 21 Refs. In Chinese.
Key Words: wind power; power system; economic dispatch; chance constrained programming; stochastic simulation; particle swarm optimization
JIANG Yue-wen (College of Elec. Eng. & Automation of Fuzhou University, Fuzhou 350002, China), CHEN Chong, WEN Bu-ying // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 37—41.

Research on effect of stray capacitance of magnetics components on CM EMI in interleaving PFC. Interleaving PFC is a common topology used in the front-end in medium and high power switched-mode power supply. This paper mainly focuses on the characteristics and mechanisms of CM EMI noises and conduction paths and presents detailed analysis about the effect of stray capacitance of the magnetic components on the CM EMI noise of power supply. From the viewpoint of stray capacitance of magnetic components, some attentions are proposed to improve CM EMI considering the EMI characteristic of interleaving PFC. And the experiments are performed based on a 600w power converter and the results verified the theoretical analysis. 7 Refs. In Chinese.
Key Words: interleaving PFC; stray capacitance; CM EFM
DONG Ji-qing (College of Elec. Eng. & Automation, Fuzhou University, Fuzhou 350002, China), CHEN Wei // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 42—46.

Synergy study for plasma-facilitated catalytic reduction of NOx. The synergistic effect of plasma-facilitated C2H4 selective catalytic reduction (SCR) of NOx over Ag/γ-Al2O3 catalyst at lower catalyst temperature was studied for the NO/NO2/C2H4/O2/N2 gas system, and a dielectric barrier discharge (DBD) reactor was used as plasma reactor. Results showed that plasma-facilitated catalysis system for NOx removal exhibited obvious synergistic effect at 240 ℃. Based on the analysis of the products of plasma pre-activation, the synergistic link products included three kinds of chemical compound like NO2, aldehydes (formaldehyde and acetaldehyde), nitrogen-contained organic compounds (methyl nitrate, nitro methyl and ethyl nitrate). The removal of NOx in DBD plasma reactor means that nitrogen-contained organic compounds yield. During the process of plasma pre-activation, improving the input energy density of DBD reactor or initial C2H4 concentration facilitated the conversion of NO2 to nitrogen-contained organic compounds and the formation of aldehydes, further improving the NOx removal efficiency of plasma-facilitated catalysis system. 10 Refs. In Chinese.
Key Words: plasma-facilitated catalysis; NOx removal; synergistic effect; plasma pre-activation; nitrogen-contained organic compound
NIE Yong (1. Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; 2. College of Chemical Engineering and Material, Zhejiang University of Technology, Hangzhou 310014, China), WANG Jing-yi, ZHONG Kan, et al. // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 47—51.

A survey on power system stochastic stability analysis and control
PENG Yun-jian, DENG Fei-qi
(College of Automation Science and Engineering, South China University of Tech., Guangzhou 510461, China)
Abstract: The paper discusses problems on random perturbations which impact the running stability and the quality of service in the power systems. And for the perturbed power systems stability analysis and stabilization controlling, basic methods based on probabilistic theory and stochastic dynamic system theory are discussed here, including random perturbations modeling, probabilistic stability analysis, the stability index and controlling strategy based on stochastic differential equations of dynamic systems, simulation tests for the stochastic power system, etc. We also present that these investigation results are important supplement for the power systems’ classic stability analysis and controlling theory. Some remaining problems and the exploration direction in this field are pointed out at end of the paper.
Key words: power systems; random perturbation; stability analysis and controlling; probabilistic theory; stochastic dynamic systems’ method

Study of specification of experiment of convertor in superconducting magnetic energy storage devices
HUANG Jin, XIONG Rui, ZOU Yun-ping, TANG Yue-jin
(Huazhong University of Science and Technology, Wuhan 430074, China)
Abstract: There is no unified specification of experiment of the convertor in superconducting magnetic energy storage (SMES) devices at present. In view of the function of SMES convertor being to exchange power in huge capacity, this paper discusses some main electromagnetic problems of the convertor such as steady-state and transient characteristics, voltage and current fluctuation, equilibrious degree, electromagnetic interference (EMI), and so on. Considering other electromagnetic problems that convertor need be assessed, a primary experiment regulation of the SMES convertor is presented. In this experiment regulation, not only some measurements of conventional convertor are used for reference, but also some important measurements and measuring processes for the SMES convertor are added. These added measurements and measuring processes are given in detail. Thus a relatively comprehensive experiment regulation of the SMES convertor is formed. Based on this, the full experiment regulation of the SMES will be studied and presented in the future.
Key words: SMES; converter; experiment regulation

An optoelectronic high-voltage probe for measuring impulse voltage distribution of HVDC converter valve. A high-voltage optoelectronic probe is developed for measuring impulse voltage distribution along thyristor units in the HVDC converter valve. The dimension of the resistive voltage divider is optimized by means of numerical computation of electric field. A pulse frequency modulation (PFM) mode is adopted for the data transmission link because of its immunity to high-intensity electromagnetic interference. Experimental results indicate that the linearity deviation for the whole measuring system is within  , and therefore it can meet requirements specified by IEC60700-1. 10 Refs. In Chinese.
Key Words: optoelectronic high-voltage probe; impulse voltage distribution; voltage divider; converter valve
FANG Zhi (1. School of Automation, Nanjing University of Technology, Nanjing 210009, China; 2. State Key Lab. of Power Equipment and Elec. Insulation, Xi’an Jiaotong University, Xi’an 710049, China), QIU Yu-chang // Adv. Tech. of Elec. Eng. & Energy, 2007, 26(3). 64—67.

Study on overlapping commutation in doubly salient brushless DC generator
GUO Hong-hao, QIN Hai-honng, DAI Wei-li, LI Jin-fei, WANG Hui-zhen
(Aero-Power Sci-tech Center, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China)
Abstract: Due to non-sinusoidal and unsymmetrical winding induced voltage, it is hard to give an exact expression of overlapping commutation angle and overlapping voltage in doubly salient brushless DC generator. Thus, the influences of excitation current, rotating speed and load level on commutation is first analyzed, and comparisons of overlapping commutation angles under different conditions are given. Also, the difference of overlapping commutation between doubly salient brushless DC generator and permanent magnet synchronous generator is deduced. Based on above analysis, the rule of overlapping commutation for doubly salient generator is obtained, and it provides a good guideline to the performance investigation of doubly salient generator.
Key words: doubly salient machine; brushless DC generator; overlapping commutation; three-phase rectifier

Analysis of exposed areas of voltage sags in a distribution system
CHEN Rui1, XIAO Xiang-ning1, TAO Shun1, ZHANG Shao-jun2, CHEN An-yuan2
(1. Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry of Education (North China Electric Power University), Beijing 102206, China;
2. North China Grid Langfang Power Supply Branch, Langfang 102800, China)
Abstract: This paper analyses the factors influencing the exposed areas, and studies the rules how to get the exposed areas from one phase to the others. Based on PSCAD/EMTDC, this paper presents a distribution system. The exposed areas of voltage sags, which could provide the basic rules for strengthening the power network, selecting the optimum operation mode, and selecting the position connecting the sensitive load with the distribution system, can be estimated by utilizing the fault simulation method.
Key words: voltage sags; exposed area; fault simulation method; sensitive load

Thermally stimulated current investigations on the insulation
WU Jian-dong, WU Guang-ning, ZHOU Kai, DENG Tao, HE Jing-yan
(Southwest Jiaotong University, Chengdu 610031, China)
Abstract: Thermally stimulated current (TSC) is an important method to study the space charge accumulation and the trapping parameter in dielectrics. This method is used to obtain the parameter of dielectrics, but the background current existing in test influences the results. In this paper, the mechanism of TSC and parasitic conduction current is discussed. The tests of parasitic conduction current and TSC to polyimide (PI) used in inverter-fed motor have been done. It is shown by the test results that the parasitic conduction current changes with the temperature rising, and the precision of TSC is affected seriously. To eliminate the interference mentioned above, a correction approach for TSC test is presented. The material parameter could be obtained more precisely from the corrected TSC curve.
Key words: polyimide; thermally stimulated current (TSC); parasitic conduction current; activation energy