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SUMMARY It is important that photovoltaic (PV) systems detect islanding caused by power system faults to ensure electrical safety. Thus we propose a novel islanding detection method which detects the harmonic impedance by injecting harmonic currents synchronized with the exciting current harmonics of the pole transformer. For the case in which an induction motor load is included in the load system, basic experiments on islanding detection and simulation analysis are conducted to verify the effectiveness of the proposed method.

We have optimized the detection unit of a previously developed AC/DC magnetometer that employs a high critical temperature superconducting quantum interference device high-T c SQUID. Optimization involves improvement of the usable dynamic range of the high-T c SQUID system during excitation with an AC magnetic field using a tuned compensation coil and an increase in the DC magnetic field resolution using a secondary excitation coil. The compensation coil technique had resulted in a single and compact detection coil using one SQUID for both AC and DC magnetization measurement functions with improved sensitivity in AC measurements. The sensitivity of the improved system is demonstrated by measuring the magnetization curve and harmonics distribution of low-concentration iron oxide nanoparticles solutions. Highly sensitive evaluation of magnetic nanoparticles in solutions can be expected with the developed system.

When large penetration of the distributed generators (DGs) such as photovoltaic (PV) systems is growing up in grid system, it is important to quickly prevent islanding caused by power system fault in order to ensure electrical safety. We propose a novel active method for islanding prevention by harmonic injection synchronized with exciting current harmonics of the pole transformer in order to avoid mutual interference between active signals. We confirm the validity of the proposed method by performing the basic tests of islanding by using a current source superimposed the harmonic active signal. Further, we carry out the simulation using PSCAD/EMTDC, and verify the fast detection of islanding.

SUMMARY With increasing penetration of distributed generators such as photovoltaic (PV) systems in distribution systems, it is very important to quickly detect islanding caused by power system faults in order to assure electrical safety. We have developed a nonlinear magnetizing characteristics model of pole transformers for use in analyzing islanding prevention in PV systems. Basic experiments on the islanding detection were performed for verification of the proposed model. Analytical results obtained by the proposed model agreed well with experimental results.

SUMMARY As distributed generators (DGs) such as photovoltaic (PV) systems are increasingly used in distribution systems, quick prevention of islanding caused by power system failure is essential to assure electrical safety. Various islanding protection methods have been used practically, but the conventional active systems tend to increase the detection time, because mutual interference occurs between active signals due to asynchronous states. A new active islanding detection method, the frequency feedback method with step reactive power injection, also has the possibility of extending the detection time in the so-called perfect balance area (PBA). Thus we propose a novel method of islanding-prevention by harmonic injection synchronized with the exciting current harmonics of the pole transformer. We performed an experimental study using prototype inverters equipped with the proposed method. We have shown the feasibility of detecting islanding quickly and reliably, even if the islanding state is in the PBA. The experimental results demonstrate that mutual interference does not occur due to asynchronous states between active signals, and also that the proposed method is applicable to islanding detection system in clustered installation of PV systems.

To establish the standard measurement method of magnetic properties of Fe-based amorphous magnetic materials, this paper investigates a single sheet tester (SST) for Fe-based amorphous magnetic materials. The influences of the material and structure of the yoke on the measurement results of magnetic properties of amorphous materials are revealed. The difference in the measurement method of magnetic field strength is also discussed from the standpoints of accuracy and repeatability. Furthermore, the difference in magnetic properties measured by a SST and a toroidal core is compared.

SUMMARY For the detection of islanding, it is very important to choose the threshold value for the change in the harmonic voltage. In this paper, we propose an analytical model of a pole transformer using a Fourier series and clarify the nonlinear magnetizing characteristics of the pole transformer in an islanding area. After determining the proposed model coefficients from the tests of the pole transformer excited by a sinusoidal voltage, distorted wave voltage tests were performed under conditions in which the third harmonic voltage or the fifth harmonic voltage was superimposed. The results of the testing showed that the magnetic properties vary greatly upon increasing the harmonic component of the voltage. The analytical and measurement results were in good agreement. By using the proposed method, the distributed generators (DGs) can estimate the magnetizing characteristics of the pole transformer by monitoring the connected terminal voltage. Thus, as an active signal for islanding detection, DGs can inject a harmonic current synchronized to the excitation current harmonics of the pole transformer into the distribution network. In the case of DGs equipped with the above functions, there is no need to change the settings of the islanding detection threshold for changes in the harmonic voltage even when there is a change in the excitation voltage or an increase in the number of DGs.

When distributed generators such as photovoltaic (PV) systems spread widely in distribution networks, it is important to detect islanding caused by power system fault for ensuring electrical safety. We developed the nonlinear magnetizing characteristics model of a pole transformer for analyzing islanding-prevention of PV system. Basic experiments of the islanding-detection were conducted by using the RLC resonant circuit for verification of the developed model. Analytical results by the proposed model agreed well with experimental results.

Purpose – The purpose of this paper is to use numerical methods and modelling to estimate the effect of a passive, metallic (conducting) implant on eddy currents distribution in a human knee model. There exists a concern among wearers of such implants that they alter electromagnetic field (eddy currents) significantly and there is a need for standardization of that problem.Design/methodology/approach – The numerical model of a human knee has been built on the base of Visual Human Project and electromagnetic field calculations were carried out using Meep FDTD engine. In total, two scenarios have been considered: the knee model with and without a metallic implant. The knee implant model has been prepared as the knee model with overestimated electrical parameters of bone tissues by titanium metal. Alternating eddy current distribution has then been evaluated for both models using FDTD low frequency algorithm.Findings – The highest values of eddy currents occurred on the interface between skin and muscle tiss...

This paper investigates the parallelization of the time-periodic finite-element method in nonlinear magnetic field analyses of rotating machines. The developed method, which can obtain the steady state solutions directly, provides large granularity even in the small-scale problems compared with the ordinary parallel FEM based on the domain decomposition approach. Furthermore, we apply the parallel TPFEM to analyses of induction motors which have different time periodicities in stator and rotor regions due to the slip. Numerical results verify the effectiveness of the developed method.

This paper presents a novel common-source active clamped complex type converter. This converter is the intermediate isolated bus converter for the distributed power supply system in telecommunications equipment. Using active clamped circuits, the switching loss and switching noise can be reduced by means of the soft switching techniques. By adding an auxiliary winding to the transformer, the proposed converter is a common-source type having direct connection of sources of the two MOSFET switches. As a result, the pulse transformer becomes unnecessary, and the drive circuit is simplified. In the experiment, at 48 V ratings input voltage, 36 to 72 V worldwide input voltage, and 12 V output voltage, the ZVS operation is performed on the main switch and auxiliary switch, and highest efficiency 92.7% is obtained. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 64–70, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20682

A single sheet tester (SST) for audio frequency of 400 Hz–10 kHz was made experimentally and the magnetizing winding can get the nearly uniform distribution of flux density of a specimen in the longitudinal direction at the frequency up to 10 kHz. The flux densities at various positions of strips measured by the Epstein method were detected by search coils wound on strips at 400 Hz and 1.0 T. They have large discrepancy. However, the magnetic properties obtained from both methods have a little discrepancy. Although the uniformity of flux distribution in the Epstein frame is not sufficient, the average is fairly effective because the magnetic properties can be assumed to be locally linear within the small deviation of flux density.

A technique for structural analysis of transformer cores in terms of magnetostriction is proposed. The magnetic flux density of each element is first calculated by the finite element method (FEM). Then the magnetostrictive force on each element is calculated from measurements. The magnetostriction is specified as the initial strain and is converted into the force on each node, and a structural analysis is performed. The advantage of specifying the magnetostriction as the initial strain is that it is possible to obtain the force at the location of each element as a vector. Modal analysis and frequency response analysis were also performed and it was shown that resonance is related to the magnetostrictive frequency and the natural mode. Thus, it becomes possible to forecast the frequency at which the core vibrates most strongly which makes the proposed technique of analysis is very useful. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(1): 19–26, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20947

In designing power electronics devices, it is very important to have accurate waveforms of input/output voltage and current in order to estimate the efficiency and the power factor. Therefore, it is useful to study the effective dynamic analysis method through a numerical approach. In these computations, the displacement current is ignored because the frequency range is lower than the megahertz range, and the necessity of taking into account the displacement current is thought to be uncertain when the transformer is operated at a frequency exceeding 1 MHz. This paper describes the effect of the displacement current on dynamic performances of a megahertz-band transformer. It is found that the influence of displacement current on output power is about 2% based on the results of computation, and becomes stronger as the frequency increases. The validity of the computation is verified through a comparison with the measured results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 60–67, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20490

In designing power electronics devices, it is very important to grasp the accurate waveforms of input/output voltage and current in order to estimate the efficiency and the power factor. Therefore, it is useful to study the effective dynamic analysis method through a numerical approach. In these computations, the displacement current is ignored because the frequency range is lower than MHz, then the necessity of taking account of displacement current is thought to be uncertain when the transformer is operated at the frequency of more than MHz.This paper describes the effect of the displacement current on dynamic performances of MHz band transformer. It is found that the influence of displacement current on output power is about 2% from the results of computation, and becomes strong according to the increase of frequency. The validity of the computation is verified through the comparison with the measured results.

Making use of the transformer leakage inductance, a self-excited continuous conduction mode ZVS flyback converter that performs self-excitation operation with a continuous conduction mode and zero voltage switching is proposed. In this converter, by turning off of one switch element, another switch element is turned on. By setting a delay time, ZVS operations are realized alternately. A new control scheme is used for independent control of each on-time of two switching elements. By means of the extended state-space averaging method, the static and dynamic characteristics are derived analytically. Then, the design equation, ZVS operating condition, and frequency characteristic of the transfer function are derived. Based on the analysis, a converter is designed and is tested experimentally for confirmation of the validity of the approach. In the experiment, efficiencies of 94.1% and 90.0% are attained, respectively, with outputs of 24 V/6 A and 24 V/15 A for an input of 141 VDC. In comparison with the converter operated in the critical current mode, the output is about 1.8 times as large and is 360 W. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(107rpar;: 18–27, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20222

In this paper, the analytic algorithm using equivalent magnetization curves is proposed for analysis of the three-phase transformer with wound-core in consideration of a step-lap joint or noncut structure. Influences of differences in step-lap joints and noncut structures on equivalent magnetization curves are examined using the algorithm. Influences on the exciting currents and core losses of the three-phase transformer are also examined.

A new analytical approach to the finite element calculation of torque in motors including eccentric rotor, based on the Maxwell stress method, is proposed in this paper, where the effects due to eccentricity on the cogging torque and the torque characteristics with regard to the speed are confirmed. A brushless dc motor is employed as an analytical model for two kinds of eccentricity. Consequently, in the case of eccentric motors, the unbalanced radial force functions as the repulsive force against rotation which causes the reduction of average torque, and two kinds of eccentric motors have the same tendency regarding the effects on the torque. This proposed approach is applicable to any kind of motor including eccentric rotor. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 53–61, 2000

This paper describes a useful method to analyze the nonlinear magnetic fields in a condenser motor considering skewed slot effects by 2-D FEM coupled problems. In this method, the exciting circuit equations, the rotor circuit equations including the currents in the end ring and the magnetic field equations are solved simultaneously. Therefore the input currents, the rotor bar currents and the currents in the end ring are obtained directly. Moreover this method is developed to consider the skewed slot effects by modifying the rotor circuits. The validity of this method is shown by comparison between the computed results and measured ones.

This paper proposes a computational method for predicting the dynamic response characteristics of a long stroke-linear solenoid actuator with complicated shaped armature. In this method, the magnetic field is coupled with the electrical supply and the mechanical movement of the actuator, employing the axisymmetric finite clement method (FEM). The influence of applied voltage on the response characteristics are investigated. As the result of that, computational error of 22.8% arises when applied voltage of 4.8 V is fed, however, the error remains less than 2% when the applied voltage is higher; 5.8 V and 6.8 V. These results verify the utility of this method. In addition, the influence of the control method on transient response during positioning control is also examined, and the validity of PID (proportional, integral and differential) control is confirmed.

This paper describes a new method for the 3D computation of a permanent magnet motor excited from a voltage source. The method has advantages that the 3D mesh as well as the circuit is changed automatically according to the movement of the armature. The method is applied to the rotating analysis of the IEEJ model excited from a square pulse voltage source. The results calculated by the 3D analysis are compared with the results by a 2D analysis. The validity of the new method is also confirmed by experiments.

This paper proposes a computational method for predicting the dynamic response characteristics of a long-stroke(7 mm) linear electromagnetic solenoid with an armature of complicated shape. In this method, the magnetic field is completely coupled with the electrical supply and the mechanical movement of the actuator, employing the axisymmetric finite element method (FEM). The utility of this method is verified by comparing the computed results with the measured results.

The purpose of this paper is to present an easy method for analyzing the operating characteristics of a separate-type transformer connected to an external circuit including elements such as batteries, resistances, and diodes. This method, a combination of two- and three-dimensional finite element methods, has been applied to a transformer connected to a compact battery charger to obtain its output characteristics. The utility of this method has been verified by comparing the measured results. >

In this paper the authors present a method to analyze the nonlinear magnetic fields with accuracy using two-dimensional finite element method in a shaded pole motor. The rotor circuit equations are coupled with the magnetic field equations, to estimate the rotor currents directly. Likewise the shading coil currents are calculated directly by coupling problems. This method is developed by modifying the rotor circuit equations to analyze the magnetic fields in the motor considering skewed slot effects. When the computed results by proposed method are compared with the experimental values, good agreements are obtained. >

In this study, the optimum shape of the magnetic pole on an electromagnetic damper is determined by means of an optimization technique with an eye to compact design. The Lagrange multiplier method was used as the optimization technique. Firstly, damping coefficients were evaluated from the distribution of eddy currents occurring in the conducting slab. The distribution of eddy currents was calculated by the boundary element method combined with the finite-element method. Secondly, the optimum shape of the magnetic pole was obtained by the optimization technique under several conditions. Thirdly, each optimum pole shape was verified experimentally through comparison between the experimental value of the damping coefficient and the objective value.

This paper investigates the acceleration of convergence to a steady state in a transient analysis of rotating machines using the time-periodic explicit error correction (TP-EEC) method. The efficient method to deal with the movement of the rotor and different time-periodicity in the fixed and moving parts of the mesh is developed. Numerical results verify the effectiveness of the developed method.

A technique for calculating the thrust of linear pulse motors is presented. This technique effectively uses the finite element method and the permeance analysis method to efficiently calculate the thrust with high accuracy. The utility of this technique was verified through the comparison of calculated and experimental results when applied to double-sided linear pulse motors with permanent magnets. The technique was applied to double-aided linear pulse motors, where the teeth of both the stator and the mover have simple rectangular shapes. The universality of this technique was verified by applying it to another model where the teeth of the mover have a trapezoidal shape. >

The optimum shape of a conductor slab on an electromagnetic damper is determined by an optimization technique by the use of the Lagrange method of multipliers taking a serious view of a compact design. Firstly, damping coefficients were obtained by analysis of the eddy current in the conductor slab by the boundary element method combined with the finite element method. The numerical result agrees well with the experimental result in our previous report. Secondly, the optimum dimension of rectangular conductor slab was obtained by the least-square method and the optimization technique. The result of the optimization is verified in good agreement with the result of the least-square method. Thirdly, the optimum shape of conductor slab determined by the optimization technique. Furthermore the result is verified by an experimention.

The fluctuation of flux density and shape effect of conductor slab on an electromagnetic damper, which consists of rectangular magnetic poles and a conductor slab, are clarified by the finite element anaysis and an experimentation. Firstly, we measured the flux density distribution near magnetic poles by the use of Hall elements, while the conductor slab vibrating in the magnetic field. The result verifies the numerical result in our first report. Secondly, attenuation coefficients were obtained under several dimensional ratios of conductor slab to magnetic pole, experimentally and numerically. The experimental result agreed well with the numerical result. Thirdly, a relation between conductor shape and eddy current distribution is also discussed numerically.

In this paper, 3-D FEM analysis is employed for these transformers, in which the external electric components, i.e., battery and diodes are taken into account. The utility was verified through the comparison of calculated and measured results.

In this paper, fundamental characteristics of the electromagnetic damper are investigated by the finite element method. A reaction of the magnetic field caused by the eddy current is considered in the formulation. In the analysis, first, the eddy current in thee conductor slab is calculated when the slab moves at a constant velocity perpendicular to the magnetic flux density, and the attenuation coefficients are obtained by the use of the calculated ones. Then the effects of the reaction of the magnetic field are analyzed with the finite element method and Runge-Kutta method regarding the analytical model as a coupled problem of the magnetic field and the vibration of the slab. Furthermore, the numerical results are verified by experiments, agreeing well with the experimental ones.

In this paper, the fundamental characteristics of the electromagnetic damper are investigated by the finite element method. The reaction of the magnetic field excited by the eddy current is considered in the formulation. Firstly, the eddy current in the conductor slab is calculated for a slab moving at a constant velocity perpendicular to the magnetic flux density, and the attenuation coefficients are evaluated in accordance with the calculated values of the eddy current. Secondly, the effects of the reaction of the magnetic field are analyzed by the finite element method and Runge-Kutta method in a couple problem involving the magnetic field and the vibration of the slab. Thirdly, the numerical results are verified through experimentation.

A model is given and a periodic boundary condition is adopted to analyze magnetic fields of a delta type shunt reactor. An approximate three-dimensional finite-element method that combines some axisymmetric fields and a two-dimensional field is then applied. It is found that the flux in the yoke concentrates on the part that is near the legs. The flux density heightens as the legs is approached, and rotational magnetic flux occurs in the parts joined by a leg and the yoke. All flux density waveforms contain mainly third harmonics. It is found that there is rotating flux in the yoke, which causes increased core losses. >