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Transformation of Sommerfeld integral formula between cylindrical coordinates and Cartesian coordinates
HUO Xiao-yun, LEI Yin-zhao
( School of Automation Science and Electrical Engineering, Beihang University, Beijing 100191, China )
Abstract: The Sommerfeld integral formula is used to solve the electromagnetic fields produced by the electric dipole in the multilayered media. In order to study the effect of the Sommerfeld integral formula in different coordinate systems on the analytical solutions of the electromagnetic fields, the magnetic vector potential of an electric dipole in an infinite space in different cylindrical coordinate systems is derived via the translation and rotation of coordinate system. Then the expression of the magnetic vector potential is transformed from the cylindrical coordinate system into the Cartesian coordinate system by the integral formulas of Bessel function and exponential function. Subsequently the relationship between the expressions of the magnetic vector potential and the rotation angles of the coordinates are discussed. Furthermore, the numerical examples are provided to demonstrate this conclusion. The analyses in this paper are expected to be helpful to uncover the underlying mathematical meaning of the Sommerfeld integral formula and to calculate the electromagnetic field produced by the transmission line above the ground.
Key words: Sommerfeld integral formula; magnetic vector potential; cylindrical coordinate system; Cartesian coordinate system
Study of calorimetric method to measure loss of super low loss angle core
WANG Jing-hui, Chen Wei
(College of Engineering & Automation, Fuzhou University, Fuzhou 350108, China)
Abstract: The calorimetric method indirectly measures the core loss by measuring the temperature rise of the magnetic component. The measurement process is not influenced by the impedance angle of the magnetic component, so it can measure the core loss more accurately. However, the existing calorimetric method can not evade the error in the measurement process, so it is not applicable to the measurement of low losses. The sources of measurement error are analysed in detail in this paper, and a novel calorimetric method by calibrating in section to eliminate the error is proposed. The calorimetric method equipment is put forward in this paper, and the results validate that it is more accurate to measure the low losses by the experiment.
Key words: calorimetric method; core losses; calibrating in section
Research on control strategy for four-leg inverter in distribution generation system
CHEN Hong-bing1,2, ZHANG Xing1, YANG Shu-ying1
(1. School of Electric and Automation Engineering, Hefei University of Technology, Hefei 230009, China;
2. School of Physics and Electronic Engineering, Hubei University of Arts and Science, Xiangyang 441053,China)
Abstract: A grid formed with distribution generators is a weak grid, and supplies power energy to all sorts of loads. According to characteristics of distribution generation grid and status of loads, a four-leg inverter has been used as an interface device for forming distribution generation system. A decomposing sequence method with band pass filter has been proposed, and a decomposing sequence control algorithm has been applied to control the four-leg inverter. The parameters of a current controller and a voltage controller have been tuned. Static-state performance of a four-leg inverter controlled by a double loop control method in synchronous rotor frame is poor, and this problem has been solved. Associated control scheme for the distributed generation system based on a four-leg inverter has been designed and constructed so as to confirm the feasibility of the proposed method. Control system static-state performance of a four-leg inverter has been thoroughly improved, and the operation ability of the distributed generation system under the unbalanced loads has been greatly enhanced.
Key words: four-leg inverter; distribution generation system; band pass filter; decomposition sequence control method
Electromagnetic characteristic analysis of a planar transmit coil
WEI Shu-feng1,2, YANG Wen-hui1, WANG Hui-xian1
(1. Institute of Electrical Engineering, CAS, Beijing 100190, China; 2. Graduate University, CAS, Beijing 100049, China)
Abstract: A planar RF coil used in vertical field MRI was analyzed in this paper. Firstly, a lumped element equivalent circuit of the planar coil was used to analyze the resonant frequency and resonant mode of the coil. Then current distribution and magnetic field distribution in different resonant modes were studied with the method of numerical calculation of electromagnetic fields. Finally, a planar transmit coil with 8 segments was analyzed. The homogeneity of the coil in a sphere of 300 mm in diameter is 15.2%, and this is close to the results measured on a real coil.
Key words: MRI; RF coil; vertical field; Numerical calculation of electromagnetic fields
Modified rotor flux observer based on statically compensated voltage model
SONG Wen-xiang, RUAN Zhi-yong, YIN Yun
（School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072,China）
Abstract: In the pure voltage model based flux observer, a LPF is normally used to replace the pure integrator to avoid integration drift and saturation problems. In order to eliminate the DC offset efficiently and compensate the error brought about by LPF as well as improve the dynamic performance, a modified rotor flux observer is proposed in this paper. In the proposed scheme, series LPF is used to remove the DC drift firstly, then a programmable LPF is used instead of the pure integrator, and the amplitude and phase error is compensated before the back EMF filtered for the flux estimation. Simulation and experiment based on induction motor speed sensor-less vector control systems verified its correctness and effectiveness.
Key words: flux observer; voltage model; low pass filter (LPF); DC offset; vector control
Reactive power optimization based on adaptive induction-enhanced particle swarm algorithm
LIU Li-jun,CAI Jin-ding
（College of Electrical Engineering and Automation, Fuzhou University, Fuzhou 350108, China)
Abstract：Reactive power optimization in power system is the effective means to improve the voltage quality, reduce system losses and ensure secure and economic operation of system. Based on analysis and comparison of genetic algorithm, simulated annealing algorithm, Tabu algorithm, and traditional particle swarm optimization algorithm for reactive power，an adaptive induction-enhanced PSO is introduced to solve the problems of strong randomness and premature convergence in last period evolution of traditional PSO in this paper. During the early search, the strategy of extrapolation in mathematics is used to update the particle position for decreasing the randomness of PSO, and colony fitness variance is used to judge the population diversity. Mutation probability is adjusted for making variant judgment to update the particle position and speed adaptively in order to improve the capability of local and global search. Calculation of a power distribution system in Fujian province shows that, the validity and feasibility of the proposed algorithm is proved. The optimal loss-lowering rate is 15.3%, and minimum voltage increases from 0.8950(p.u.) to 0.9973(p.u.).
Key words: particle swarm optimization；induction-enhanced；adaptive mutation；reactive power optimization
Speed sensor-less direct torque control of induction motors based on sliding-mode observer
SUN Zhen-xing, ZHANG Xing-hua
(College of Automation & Electrical Engineering, Nanjing University of Technology, Nanjing 210009, China)
Abstract: Sliding-mode variable structure control is one of the effective synthesis methods for nonlinear systems, which is characterized by simple control scheme, fast dynamic response and strong robustness to the parameter variation and external disturbance. In this paper, a novel sliding-mode observer for stator flux estimation is proposed. This observer employs stator currents and flux as the state variables, and uses the error of the stator current estimation to adjust the flux observer. The convergence of the observer is proved by Lyapunov’s stability theory. Then, a speed sensor-less direct torque control system of induction motor drives based on the sliding-mode flux observer is designed, which uses the slip frequency method to calculate the speed on real time. The experimental results show that the proposed the control scheme possesses the features of fast torque response, accurate speed tracking and wide range of speed.
Key words: induction motor; direct torque control; sliding-mode observer; speed sensor-less
Induction machine model using flux linkage as state variables including saturation
DANG Jie1, ZHANG Ming1, SUN Xi-dong2
(1. Key Laboratory of Control of Power Transmission and Conversion, Ministry of Education, Department of Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; 2. China Shipbuilding Heavy Industry Corporation No. 703 Institute of Wuxi Division, Wuxi 214151, China)
Abstract: With increased penetration of wind energy in power generation, the fault analysis of wind farm is drawing more and more attention. The calculation of short circuit current contributed from wind farms has significant impact for wind farm protection and power system stability, and advanced wind generator models are demanded for the fault analysis and relay setting of wind farm. This paper investigates Type I wind turbine-generator, and a novel model of induction machine using flux linkages as the state variable including saturation is proposed. The improvement of calculation accuracy and efficiency is validated by comparing simulations of short circuits in various commercially available simulation packages.
Key words: Wind generators; induction machine; dq model; flux linkage; magnetic saturation; wind farms;fault protection
Study of oil-paper insulated transformers’ aging state based on depolarization current measurements
TANG Pan, YIN Yi , WU Jian-dong, YAN Xu
（Department of Electrical Engineering, Shanghai Jiaotong University, Shanghai 200240, China）
Abstract: Transformer oil-paper insulation is a typical composite dielectric. And its dielectric properties will change significantly during aging process. To investigate the characteristic parameters of dielectric response phenomena of transformer oil-paper insulation aging, a simulating device of the transformer oil-impregnated pressboard insulations was designed. Depolarization current of the samples during accelerated electrical aging process at the same temperature was measured. And the infrared spectrum was used to prove that the oil-paper insulation has been aged. Based on Debye model, the resistance and capacitance of the maximum and minimum time constants branch are calculated. The results reveal that, the transformer condition can be obtained from Debye model. In Debye model the parameters Rmax and Cmax are related to aging condition of oil, and Rmin and Cmin are related to aging condition of paper.
Key words: oil-paper insulation； Debye model； depolarization current；electrical ageing；insulation condition；interfacial polarization
Fault location of distribution network based on minimal coefficient of variation using identifying model
QU Guang-long, YANG Hong-geng
(School of Electrical and Information, Sichuan University, Chengdu 610065, China)
Abstract: This paper presents a method for locating short-circuit faults using voltage sags identifying model based on the minimal coefficient of variation. When we know the characteristic of the voltage sags in different place,it is possible to find the fault section. The basic idea of this paper is to build a voltage sags identifying model under different type of faults, and comparing the voltage sags measured by the monitors on-line with the model to compute the coefficient of variation, then the minimal coefficient of variation corresponds to the fault section. This method combines the fault line selection and fault section location in distribution network, and the results of the simulations emulated by EMTDC show that the method is accurate and effective.
Key words：voltage sags identifying model; coefficient of variation; distribution network
Partial discharge characteristics of twisted pairs for inverter-fed motor under square impulse voltage
XU Hui-hui，WU Guang-ning，ZHU Guang-ya，LUO Yang，CAO Kai-jiang，ZHANG Yi-qiang
(School of Electrical Engineering , Southwest Jiaotong University , Chengdu 610031, China)
Abstract: Inverter-fed traction motor is one of the key components in electric locomotive for high-speed railway, of which insulation system reliability can guarantee the safety and stability of locomotive. Partial discharge（PD） is one of the most important factors causing previous failure of the insulation of inverter-fed motors. In this paper, a partial discharge testing system under square impulse voltage based on impulse current sensor was built. And PD tests were conducted on twisted pairs simulating inter-turn insulation of inverter-fed motor. The influence of voltage rise-time and frequency on PD inception voltage, average discharge quantity, and discharge numbers were analyzed. Meanwhile this paper discussed the PD mechanism of the twisted pairs under square impulse voltage. This can provide more strong foundation for further studies on insulation ageing mechanism of square impulse voltage.
Key words：square impulse voltage; partial discharge; inverter-fed motor; twisted pairs
A practical fault locating adaptive algorithm for distribution network with distributed generation
WU Le-peng, HUANG Chun, ZEN Zhao-xing
(College of Electrical and Information Engineering, Hunan University, Changsha 410082, China)
Abstract：The premise of effective use of clean energy is to correctly determine the malfunction zone of distribution network with distributed generation. Based on the matrix algorithm in the location of feeder terminal unit (FTU) to the malfunction of distribution network, anA adaptive algorithm for the fault location in distribution network is proposed. According to the overcurrent flowing through the FTU and its direction, firstly the algorithm judges whether distributed power is put into operation, and whether the fault happens at bus and network. Then it preliminarily locates the malfunction zone in the distribution network. Secondly, on the basis of malfunction zone structure and overcurrent information of FTU, the fault matrix is adaptively formed and the fault zone is confirmed. Lastly, according to the defected fault current difference at both ends of fault circuit to form the fault criteria, the proposed criteria are formed by comparing the difference between fault current . The numerical example verifies accuracy and efficiency of the algorithm, and good mechanism of fault tolerance.
Key words：distributed generation; distribution network; FTU; fault location; adaptive algorithm
Input-to-output stability theory and its application on isolated power system
ZHANG Xue-min, CHEN Lai-jun, MEI Sheng-wei
（State Key Lab of Power Systems, Dept. of Elec. Eng., Tsinghua University, Beijing 100084, China）
Abstract: For practical dynamic system, Lyapunov stability theory focuses on the ability of a system to go back to certain equilibrium from arbitrary initial point if there is no external input signal. Thus, Lyapunov theory is not suitable for analysis whether a system’s state can be bounded by a pre-set region when the system has persistent disturbances (including bounded external signal). For this reason, Input-to-State Stability (ISS) theory came into being. The theory unifies Lyapunov method and operator approach, and proposes the concept of ISS, definitions, models and methods systematically. Recent progresses, such as the automatic analysis method for local ISS and interconnection system’s ISS small gain theorem, provide theoretical basis for ISS to be applied in isolated power systems. This paper provides comprehensive overview of ISS basic theory, research achievement and application in isolated power system.
Key words: ISS, local ISS-Lyapunov theorem; ISS small gain theorem; isolated power system
Study of temperature measurements with thermocouple under high-frequency magnetic field
LIN Su-bin，CHEN Wei，WANG Jing-hui
(Fuzhou University, Fuzhou 350108, China)
Abstract: The measurement error of temperature by thermocouple is very large when it’s used to measure the temperature in environment with high-frequency magnetic field. In this paper the mechanism of errors is analyzed to find that the error was due to eddy-current effect on the metal tip of the thermocouple. The thermocouple temperature measuring platform in high-frequency magnetic field was built. With the results of measurement, temperature rising model of K type thermocouple under the sine wave magnetic field was set by use of multiple nonlinear regression algorithm in order to amending the influence of eddy current effect. Based on the method of weighted average equivalent sine frequency, sine wave of magnetic field temperature rising model is applied to triangular wave magnetic field. Experiments verified the temperature rising model is accurate enough for the sine wave, and even for the triangular wave high-frequency magnetic field.
Key words: thermocouple; high-frequency magnetic field; temperature rising model; eddy current
Study of miniaxial flow turbine in energy-saving cooling towers
GUO Run-rui1，ZHANG Guo-qiang1，SHI Jin-hua2，FEI Xiao-yong2
(1. Institute of Electrical Engineering，Chinese Academy of Sciences，Beijing 100190，China；2. Nanjing Dayang Cooling Tower Co.,Ltd ，Nanjing 211307，China）
Abstract：In energy-saving cooling towers, the miniaxial flow turbine are applied to drive cooling tower fans to replace motors in the conventional cooling towers. With the applied technology, the cooling towers can make full use of the surplus energy of circulating cooling water, while saving the energy consumption of fan motors of cooling towers. However, at present,the working mechanism of mini-hydraulic turbines driving cooling tower fans has not been adequately studied in our country,leading to many non-ideal engineering cases. Based on analyzing the condition of the cooling tower and the structure and performance characteristics of all types of hydroturbine, application criterions and technical specifications of selecting structure type of micro-turbine have been worked out, and then, some application research of axial flow turbine has been done. Experimental results demonstrate that the miniaxial flow turbine applied to drive cooling tower fans has good performance, and relevant research results have been applied in many projects and have get significant energy-saving effect.
Key words：cooling tower；surplus energy；miniaxial flow turbine
A magnetic field compensation system for laser MRI
ZHAO Wuyi1,2, WANG Huixian1, WANG Zheng1, ZHANG Yuxia1, YANG Wenhui1
(1. Institute of Electrical Engineering, CAS, Beijing 100190 ,China; 2. Graduate University, CAS, Beijing, 100049)
Abstract: A magnetic field compensation system has been developed for laser MRI. It can be integrated with the magnetic cycling system, extending the applicability of laser MRI to a stationary sample. It consists of Helmholtz coil and constant current source. According to the requirement of laser MRI, a simulation of the magnetic field has been done and the coils have been built. Then a feedback high precision constant current source has been developed. The results show that the earth magnetic field in the target area can be reduced to below 100nT, and the long term stability is better than 2×10-4A.
Key words: laser MRI; Helmholtz coil; constant current source
Applied research on a high-Q resonant wireless power transmission technology
TANG Wei，YANG Rui-xia，GUO Zhi-tao，GU Jun-hua
（Hebei University of Technology，tianjin 300401，China）
Abstract：An improved resonant energy transfer method based on high Q value was proposed to solve the problem of short wireless power transmission distance and low efficiency in the loose coupling of electromagnetic induction mode of percutaneous wireless power supply system. First, the theoretical model of the resonant energy transfer and the role of Q in energy transfer efficiency were analyzed. Second, in order to reduce the influence of source resistance and load, the basic circuit of percutaneous induction was improved by adding a pair of resonance coil between load coil and power coil. Finally, an experimental test device was set up to build comparative experiment, in which system Q value is increased by adding the resonant coil, and energy transfer efficiency was improved by four times and the transmission distance has also been significantly improved. Therefore, it proves the effectiveness of the method.
Key words：High Q-value；percutaneous wireless power supply； magnetic coupling；resonance
Software and hardware design of intelligent monitor and control terminal for low-voltage distribution system
XU Jia-zhu, LI Xiao-fang, HUANG Ji-yuan, YAO Xin-li, XIANG Bo, LIAO Wen-di
(Hunan University, Institute of Electrical and Information Engineering, Changsha 410082, China)
Abstract: An intelligent monitor and control terminal for low-voltage distribution system based on GPRS is presented for the rural power distribution area where the parameter calculation, intelligent var compensation and remote monitoring are famine. The terminal adopts mixed-signal ISP FLASH MCU C8051F020. Its hardware is composed of system and interface. The system is composed of modules: CPU, memory, clock chip, keyboard/liquid crystal display, reset and peripheral circuit, and the interface circuits include three-phase current/voltage transformer, energy measurement IC, RS-485communication, GPRS module, switch state detection，temperature and oil liquid of transformer and so on. Its software is based on μC/OS-Ⅱ embedded operating system，with multi-task and multi-buffer framework. The terminal not only can rapidly detect and real-time dynamically compensate var ，but also can measure the diversified parameter of transformer accurately，and thus satisfies exact data transmission between control terminal and host computer. The device is easy to be popularized because of its high accuracy，good reliability and low prices.
Key words: reactive power compensation;MCU C8051F020;intelligent terminal;GPRS;RS-485
A practical method for determining parameters of load model of distributed network with small hydro power
ZHANG Yuan-sheng1, LI Xin-ran1, XIAO Yuan-yuan1, SONG Jun-ying2, MA Ya-hui1, LIU Qian-yong1
（1. College of Electrical and Information Engineering, Hunan University, Changsha 410082，China；
2. Hunan Power Dispatcher and Communications Center, Changsha 410077, China）
Abstract: This paper takes the distributed network with small hydro power as research subject and the operating characteristics were studied. The typical 10kV small hydro simulation network of Chenzhou power grid in Hunan province was constructed in PSASP simulation environment, and the grid-connection style and the influence on the characteristic of the synthesis load modeling of the distribution network were analysed. On this basis, in order to find a better model to apply to this kind of distributed network, the weighted aggregation method was applied to get the parameters of generator of the equivalent small hydropower network model. And the operation information of the actual grid was used to determine the equivalent impedance of distribution network. The results showed that, the equivalent method can well reflect the dynamic characteristic of the hydropower,and the method has high accuracy, strong practicability and strong feasibility on the research of the actual small hydropower system.
Key words: small hydro; distributed generation; synthesis load model; weighted average method; distribution network impedance equivalent
Applications of gas discharge tube for switching mode power supply
Zhou Yan1, YANG Chang-ye2
(1.Nanjing University of Posts and Telecommunications, Nanjing 210006, China;
2. Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101, China)
Abstract：The gas discharge tube (GDT) is often used for surge voltage suppression in switching mode power supply. This paper introduces some basic GDT’s characteristics at first, such as DC spark over voltage, impulse spark over voltage, discharge current curve when the GDT is applied with different voltages, the technological requirements and the technical standards. The paper chiefly discusses two configurations for the common-mode surge voltage suppress circuit: voltage dependence resister in series with glass GDT and voltage dependence resister in series with ceramics GDT. According to the GDT working characteristics, the different types of GDTs will show different surge voltage suppression performances. Compared with the glass GDT, the ceramics GDT shows a faster response to a defined impulse surge voltage. Finally, the paper summarizes the performance of GDTs for surge voltage suppress in switching mode power supply, and gives some conclusions for selecting and using GDT. The experiment results verify the theoretical analysis.
Key words：gas discharge tube (GDT); surge voltage; switching mode power supply; surge suppression
Load characteristics classification based on adaptive genetic algorithm
BAI Jian-xun1, YANG Hong-geng1, WU Chuan-lai1, TANG Shan2
(1. School of Electrical Engineering and Information , SiChuan University, Chengdu 610065,China;
(2. Yingxiuwan Plant of Sichuan Electric Power cooperation, Chengdu 611830,China )
Abstract: A new method based on improved genetic algorithm is presented for load characteristics classification．The best individual which is of the highest fitness can be obtained by genetic manipulation on samples, and the individual is decoded to get the best cluster center, then the optimal classification is obtained by dividing samples based on the distance of the samples and the cluster centers，and finally the samples are fitted with the cluster centers of respective categories to test the classification accuracy．While ensuring the overall performance and randomness of adaptive genetic algorithm, the adaptive changing of the crossover probability and mutation probability with the process of evolution proposed in this paper can avoid the premature convergence and slow convergence which may appear in traditional genetic algorithm．Practical examples show that it can avoid the excessive impact of the initial conditions on the classification results and achieves desired classification results when classifying load characteristics with adaptive genetic algorithm．
Key words: load characteristics classification; clustering; genetic algorithm; adaptive; measured response space
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