Abstracts of Vol.25, Issue 1, 2006

Progress and perspective of the application of high temperature superconductivity.
The progress of the high-temperature superconductor, its power and magnet application is comprehensively presented. The big pressure faced to enhance the conductor performance and to reduce significantly its cost and the concentrated effort to develop 2nd generation conductor are shortly described. Based on many related discussions and the visit to USA last spring, some suggestions are presented. 1Ref. In Chinese.
Key words: high-temperature superconductivity; conductor; power application; magnet application
YAN Lu-guang (Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 10080, China) // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 1-4.

Interharmonics calculation using cross- high- order spectral Pisarenko method.
The problem of interharmonics in electric power system is becoming increasingly severe. It is a problem pressing for solution to measure the amplitude value and frequency of interharmonics exactly. Using the cross-high-order spectral Pisarenko method, the amplitude value and frequency can be calculated exactly. Based on the cross-high-order cumulant Yule-Walker, first the feature space is decomposed as signal and noise subspace, then the characteristic polynomial is constructed, and the amplitude value and frequency of each order are calculate. The result of simulink and test showed that under low ratio of signal and noise and short data, the measurement accuracy of frequency excel 0.03% and the measurement accuracy of amplitude excel 5%, and the spectral estimation has strong resolution and good stability. 5 Refs. In Chinese.
Key words: power system; interharmonics calculation; cross-high-order spectral; harmonious decomposition
LAN Hua (Dept. of Elec. Eng., Northeast China Institute of Electric Power Engineering, Jilin Jilin 132012, China), SUN Liang (Dept. of Elec. Eng., Northeast China Institute of Electric Power Engineering, Jilin Jilin 132012, China), SHI Yao-wu (Jilin University, Jilin Changchun 130000, China) // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 5-8.

Development of electric traction system based on indirect field-oriented vector control scheme.
In this paper a vector controlled AC speed-regulating system is developed, which adopts the rotor flux field-orientated theory to meet the requirements for an electric traction system. The adopted vector control theory and the control scheme are introduced, the configuration of both the main circuit and the control board system are presented, and the control scheme is explained. Based on theoretic analysis, a simulation platform is designed to help thorough research, and furthermore, an experimental system is set up to realize all these control schemes. Results from both simulation and experiment verify the excellent qualities of this system. 9 Refs. In Chinese.
Key words: electric traction; speed regulating system; vector control
WANG Yue (Xi’an Jiaotong University, Shanxi Xi’an 710049, China), DONG Qiang (Xi’an Jiaotong University, Shanxi Xi’an 710049, China), WANG Jiang-bo (Xi’an Jiaotong University, Shanxi Xi’an 710049, China, et al. // Adv. Tech. of Elec. Eng. & Energy), 2006, 25(1): 9-12.

A novel fault location algorithm for double-circuit transmission lines based on distributed parameter.
A new fault location algorithm for double-circuit transmission lines is described in this paper. The proposed method uses data extracted from two ends of the transmission lines and thus eliminates the effects of the source impedance and the fault resistance. The distributed parameter model and the modal transformation are also employed. Depending on modal transformation, the coupled equations of the lines are converted into decoupled ones. In this way, the mutual coupling effects between adjacent circuits of the lines are eliminated and therefore an accurate fault location can be achieved. The proposed method is tested via digital simulation using EMTP in conjunction with MATLAB. The test results corroborate the high accuracy of the proposed method.  13 Refs. In English.
Key words: double-circuit transmission lines; fault location; distributed parameter; phase-mode transformation; two ends data
SHANG Li-qun (School of Elec. Eng., Xi’an Jiaotong University, Shanxi Xi’an 710049, China; School of Elec. and Control Eng., Xi’an University of Science & Technology, Shanxi Xi’an 710054, China), SHI Wei (School of Elec. Eng., Xi’an Jiaotong University, Shanxi Xi’an 710049, China) // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 13-16.

Research of a current-double-rectifier zero-voltage and zero-current-switching (ZVZCS) three level DC/DC converter.
The phase-shifted ZVS is often used in the three-level dc/dc converter, but for the general phase-shifted ZVS converter, it is difficulty for its lagging-arm switches to realize ZVS, and also the converter’s efficiency can be reduced by the circular current in the period of the switches commutating. On the other hand, the larger current of the full-wave rectifier makes the size of filter and transformer increased, and at the same time the stress of the rectifier’s diodes is increased. It is not suitable to be used in the occasion of lower dc-voltage and larger current. To overcome those weaknesses, a current-double-rectifier ZVZCS three-level dc/dc converter is proposed in this paper, which realizes zero-voltage-switching for the leading switches and zero-current-switching for the lagging switches, and it is effective to avoid the influence of the circular current, and lower the stress of the rectifier’s diodes. For the sake of reduction of the current of the filter inductor and transformer, the current-double rectifier is designed in this ZVZCS three-level dc/dc converter. Both theoretical analysis and experimental results confirm the validity of the proposed design. 6 Refs. In Chinese.
Key words: DC/DC converter; zero-voltage-switching; zero-current-switching; current-double rectifier; three-level
ZHANG Xing (School of Electrical Engineering and Automation, Hefei University of Technology, Anhui Hefei 230009, China), WANG Ling-xiang (School of Electrical Engineering and Automation, Hefei University of Technology, Anhui Hefei 230009, China), Yang Shu-ying (School of Electrical Engineering and Automation, Hefei University of Technology, Anhui Hefei 230009, China), et al. // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 17-20.

Comparison of axial magnetic field characteristics of 5 axial magnetic field vacuum interrupter contacts.
Characteristics of axial magnetic field (AMF) of 5 kinds of vacuum interrupter contacts were studied with 3D finite element method, which included characteristics of AMF, eddy current in contact plates and phase shift time. The 5 AMF vacuum interrupter contacts include coil type, cup type, bipolar type, quadrapolar type and two coils type. The results showed that (1) from strong AMF to weak one generated by current, axial magnetic flux density at current peak followed with the order of coil type, bipolar type, two coils type, cup type and quadrapolar type; (2) from weak AMF to strong one at current zero, the order was quadrapolar type, bipolar type, cup type, two coils type and coil type; (3) from short phase shift time to long one at strong AMF, the order was bipolar type, quadrapolar type, coil type, two coils type and cup type. 9 Refs. In Chinese.
Key words: vacuum interrupter; axial magnetic field; vacuum arc
WANG Zhong-yi (Department of Electrical Engineering, Xi’an Jiaotong University, Shanxi Xi’an 710049, China), LIU Zhi-yuan (Department of Electrical Engineering, Xi’an Jiaotong University, Shanxi Xi’an 710049, China), ZHANG Xuan (Department of Electrical Engineering, Xi’an Jiaotong University, Shanxi Xi’an 710049, China), et al. // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 21-25.

Influence of excitation time constant on dynamic stability of power system.
Excitation time constant influences greatly on stability of power systems. According to analysis of roots locus, fast excitation tends to decrease damping of power systems which is controlled by AVR than slow excitation. But eigenvalues of power system are far from imaginary axis and strong damping is obtained when fast excitation system is added. On the contrary, eigenvalues of power systems are near imaginary axis and weak damping is obtained when slow excitation system is installed. Eigenvalues analysis and transient simulation results are given based on a 8-machine system which is controlled by AVR, AVR+PSS and decentralized & coordinated excitation law. From the results a conclusion is confirmed that fast excitation is more beneficial than slow excitation for improving dynamic stability of power systems. The mathematics essence is discovered on the basis of eigvalue-eigenvector theory. It is important to realize that fast excitation is characterized by dual effect, it maybe result in both much stronger dumping and much weaker damping than slow excitation. 11 Refs. In Chinese.
Key words: power system; excitation system; time constant; dynamic stability; eigenvector analysis
HAO Zheng-hang (Dept. of Elec. Eng., Guizhou University, Guizhou Guiyang 550003, China), CHEN Zhuo (Dept. of Elec. Eng., Guizhou University, Guizhou Guiyang 550003, China), QIU Guo-yue (Dept. of Elec. Eng., Guizhou University, Guizhou Guiyang 550003, China), et al. // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 26-29.

A control scheme of SPWM inverters based on self-adaptive fuzzy control.
As the sine wave inverter is highly nonlinear and has variable parameters due to its special structure of complicated multi-stage power converter, the perfect control can not be obtained with conventional control methods especially under nonlinear rectifier loads. A Self-adaptive Fuzzy control in this paper is applied to single-phase SPWM inverter. Assistant Fuzzy controller is designed to improve the self-adaptive and robust property through adjusting the scaling factor of main fuzzy controller on-line. The structure and parameters of main circuit are provided in the paper. Design processes of main fuzzy controller and assistant fuzzy controller are also given in detail. By this design the inverter can not only stabilize the output sine waveforms but also realize rapid transient response under variable loads. Experiment result of 3kW prototype verifies the Self-adaptive Fuzzy controller of scaling factor self-adjusting. 7 Refs. In Chinese.
Key words: inverter/Fuzzy control; self-adaptive control; rectifier load; DSP
GU He-rong (College of Electrical Engineering, YanShan University, Hebei Qinhuangdao 066004, China), WANG De-yu (College of Electrical Engineering, YanShan University, Hebei Qinhuangdao 066004, China), WU Wei-yang (College of Electrical Engineering, YanShan University, Hebei Qinhuangdao 066004, China) // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 30-34.

Method for elimination of DC offset and steady state error for voltage module flux observer.
The flux observer based on voltage has been obtained more attention for its clear concept and simple usage. However, the inherent initial value error and dc offset problem can not be completely removed using the existing low pass filter (LPF) method. Besides, LPF also brings steady state error. In the proposed method, the pure integrator is replaced by low pass filter and high pass filter (HPF) in series to eliminate the initial value error and dc offset effect, and the steady state error can be compensated completely. So the flux has no amplitude and phase error. The compensation formula is derived with time phasor method. The novel observer is simple and easier to apply to digital system. Both simulation and experimental results show that the induction motor performance in low speed region has been improved remarkably. This also verifies the effectiveness of the novel observer. 5 Refs. In Chinese.
Key words: flux observer；DC offset；time phasor；error compensation
ZHANG Xing (Dep. of Elec. Eng., Tsinghua University, Beijing 100084, China), QU Wen-long  (Dep. of Elec. Eng., Tsinghua University, Beijing 100084, China), LU Hai-feng (Dep. of Elec. Eng., Tsinghua University, Beijing 100084, China) // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 39-43.

Generalized coordinates transformation theory of multiphase system.
Circuit coordinates transformation method is one of the most important tools in analyzing and solving power system problems. In this paper, a generalized coordinate transformation theory of multiphase system including three-phase system is proposed, and also the basic properties of the theory are given. Then the essence of the transformation is analyzed from the perspective of physics and geometry, which reveals the nature of the time-space symmetry of the proposed transformation. In fact this coordinate transformation projects the interested high-dimensional signal onto a set of orthogonal subspaces. So one can study the signal in some much lower-dimensional subspaces, specifically, some planes. It can be seen that the proposed theory greatly generalizes the traditional transformation theory for three-phase circuit, and then, is in favor of establishing a theoretical foundation for harmonic detection, motor control, and fault diagnosis of multiphase system. Finally, the harmonic detection problem in multiphase circuits is addressed as an illustrative example. 7 Refs. In Chinese.
Key words: multiphase system; transformation; harmonic detection
CHEN Ju-ming (State Key Lab. of Power System Dept. of Elec. Eng., Tsinghua University, Beijing 100084, China), LIU Feng (CAS-Academy for System Science, Beijing 100080, China), MEI Sheng-wei (State Key Lab. of Power System Dept. of Elec. Eng., Tsinghua University, Beijing 100084, China), et al. // Adv. Tech. of Elec. Eng. & Energy, 2006, 25(1): 44-48.

Research on axial vibration characteristics of transformer windings under steady condition
JI Sheng-chang1, WANG Jun-de2, LI Yan-ming1
（1. Xi’an Jiaotong University, Xi’an 710049, China; 2. ABB (China) Ltd, Beijing 100016, China）
Abstract: The winding axial vibration at steady condition provides useful information about winding fixation conditions. It is necessary to study the axial vibration characteristics of windings under steady condition. Based on the actual structure of transformer windings, a mathematical model of transformer windings′ vibration is developed, and it is applied to study the vibration characteristics of windings under steady operation. The relationships between windings′ compression level and windings’ intrinsic frequency, windings′ vibration acceleration signals are analyzed，it can be concluded that the tighter the winding is compressed, the higher each order intrinsic vibration frequency is. With the augment of pre-compression, vibration-acceleration takes on a descendent trend. This phenomenon shows that the variation of winding pre-clamping pressure can be reflected. It is proved that the variation of windings’ compression can be reflected from the vibration acceleration signals. This may provide a theoretical basis for on-line monitoring of winding condition of transformer by vibration method.
Key words: transformer；winding；pre-compression；vibration；nature frequency

Design of nonlinear auxiliary power controller
for HVDC converters in non-parallel operating AC/DC systems
ZHANG Xiu-zhao, SHEN Chen, MEI Sheng-wei
(Dept. of Elec. Eng. and Applied Electronic Technology, Tsinghua University, Beijing100084, China)
Abstract: A nonlinear auxiliary controller for HVDC converters in AC/DC power systems, where the AC and DC lines are not in parallel connection, was developed to damp inter-area oscillations. The method treats the dynamic of DC power regulation as a first-order inertia block and simplifies the AC/DC multi-machine system into a two-machine power system. Based on the obtained third-order model, state-feedback linearization and LQR approach are applied to design a nonlinear controller. Computer simulation results have shown that the controller can effectively damp inter-area oscillations and enhance transient stability. But the auxiliary control for HVDC converters also introduced some undesirable side effects. Possible problems and future work are discussed at last.
Key words: power system stability；HVDC systems；inter-area oscillation；state-feedback linearization