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This paper proposes a method for detecting the angle of a bearingless motor with less magnetic interference due to the current. Bearingless motors have suspension windings and motor windings that generate leakage flux. Owing to this electromagnetic phenomenon, the signal of the linear Hall‐effect sensor for angle detection is disturbed, and it has to be avoided to place Hall sensors near the winding conventionally. To solve this interference problem, this paper clarifies the ideal combinations between sensor positions and the number of poles and slots of concentrated winding bearingless motors. [ABSTRACT FROM AUTHOR]

A separable connector is used for the power cables and apparatuses in renewable energy systems. The shield of the collector cable is sometimes an open circuit at one end to reduce power loss due to the shield current. However, this has a disadvantage from the viewpoint of lightning protection. The semiconductive part of the separable connector is grounded for safety. The ground potential rise due to a direct lightning strike to a wind tower sometimes damages the collector cables and power apparatuses in the wind tower. Combustion in a cable is one of the most serious types of lightning‐caused damage. This paper describes an experimental study on fire ignition in a collector cable caused by a ground potential rise due to a direct lightning strike to a receptor. The mechanism leading to fire ignition is discussed based on the experimental results. This paper also proposes a countermeasure against such fire ignition. [ABSTRACT FROM AUTHOR]

In recent years, wind power generation has been promoted as a countermeasure to global environmental problems. However, the introduction of many wind power generators into the power system may cause system frequency fluctuations. This paper proposes a control method to reduce system frequency fluctuations by using the rotor kinetic energy (RKE) of a variable speed wind turbine (VSWT). When the frequency falls, this method suppresses fluctuations by consuming RKE to increase VSWT power generation, and when it rises, it decreases VSWT power generation by accumulating RKE. The effectiveness of this method is confirmed through simulations using PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

In this paper, a reference stator flux linkage calculation method is proposed for realizing maximum efficiency operation in direct‐torque‐controlled interior permanent magnet synchronous motor (IPMSM) drives. The proposed method is based on the solutions of a quartic equation, a motor model in the d‐q rotating frame widely used for synchronous motor controllers, and a well‐known equation for maximum efficiency operation. Therefore, the proposed method uses neither any approximation function nor any look‐up table that depends on the parameters of the motor, which has to be created in advance. Simulation results validate that the proposed methods can achieve maximum efficiency operation in IPMSM drives. [ABSTRACT FROM AUTHOR]

The paper proposes a method to select a power factor for an inverter of distributed power generation systems to keep appropriate voltage of a power system with the high penetration of inverter‐interfaced generation. The increase of inverter‐interfaced power sources, such as wind and photovoltaic power generation, arouses concerns on the voltage fluctuations in a power system. While constant power factor control of an inverter has been studied as a means to stabilize the voltage of a power system, there still remains room to improve the control. The proposed method in the paper selects the power factor based on the R/X ratio of the looking‐back impedance into the interconnected power system. By normalizing the related variables, a general formula is derived for the power factor, and the resultant relationship between the apparent power and voltage of an inverter becomes identical irrespective of the R/X ratio with the control. Sample studies show that, by operating an inverter with the power factor, voltage fluctuations are effectively suppressed even for a power system with the high penetration of inverter‐interfaced generation. [ABSTRACT FROM AUTHOR]

Single‐phase loads and photovoltaic generation cause three‐phase imbalance in distribution systems, and prospective growth of normal chargers of electric vehicles may even increase the imbalance. The analysis of such unbalanced systems requires the three‐phase power‐flow calculation. Since existing methods require the admittance matrices of three‐phase transformers, they must be derived for all possible winding connection patterns in advance to its computer‐code implementation. This paper proposes a three‐phase power‐flow calculation method which formulates circuit equations using the modified nodal analysis, making it possible to automatically handle any winding connection. The power‐flow constraints are then embedded into the circuit equations using a fixed‐point iteration. Newton‐Raphson, backward/forward sweep and fixed‐point iteration methods are the existing three categories of solution methods. Newton‐Raphson methods may show convergence problems due to the high R/X ratios of distribution lines. Backward/forward sweep methods cannot be used, because loops are temporarily formed in a distribution system during circuit switching. These justify the use of a fixed‐point iteration. In this paper, the proposed method is validated by practical examples. [ABSTRACT FROM AUTHOR]

This paper describes the dielectric breakdown characteristics of oil and oil-impregnated paper for very fast transient (VFT) voltages. Blumlein circuits generate VFT voltages of 60 and 300 ns in a pulse width that simulates disconnecting switching surges in gas-insulated switch gears. We measured the breakdown voltages of needle-to-plane, plane-to-plane oil gaps and several pieces of paper between plane electrodes for VFT and lightning impulse voltages. The measured data were formulated in V-t characteristics and Weibull probability distributions. The inclination n of V-t characteristics of insulating paper is 150, which is less than n = 13.7 of the plane-to-plane oil gap in the VFT time range. The shape parameters of Weibull distribution obtained in this study show that the scattering of breakdown voltages of paper is much less than that of oil. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 16–24, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10043 [ABSTRACT FROM AUTHOR]

Large power transformers using perfluorocarbon liquid have advantages of high dielectric strength, excellent cooling ability, and nonflammability. To make the transformer more compact, it is very important to improve the insulation material. Recently, the authors succeeded in developing a new type of aramid insulation paper which has no fluff on its surface to avoid field concentration. In this study, an outline of the developed paper and the experimental results of the insulation strength on turn-to-turn and intercoil models are described. It was found that the new aramid paper increases the insulation strength 1.2 (turn-to-case) to 1.7 (intercoil case) times that of the existing insulating paper. [ABSTRACT FROM AUTHOR]

More and more electronics are intended for use in adverse environments at high temperatures with high humidity. The spatial distributions of internal charge carriers, mainly due to ionic impurities that appear in hot and humid environments, are considered to affect the reliability of bulk insulation. Therefore, the authors examined space charge behavior inside paper/phenol-resin composites for printed circuit boards under DC voltages, focusing on the effect of the water absorption temperature. Both the sample weight and thickness were increased monotonically by immersion in water with an increase in the water temperature from 24 to 85 , indicating that the water absorption by the sample was temperature dependent. In the early periods of water absorption (up to 10 hours), the electric field decreased near the two electrodes and increased in the other regions. Furthermore, heterocharge formation was observed near the cathode as the water absorption progressed, becoming more significant at higher water temperatures. Ion chromatography analyses detected numerous ions such as Na+, $NH_{4}^{+}$ and Cl- from the water, in which the sample had been immersed for 100 hours at various temperatures. It is highly possible that these ions are responsible for the heterocharge formation. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(2): 1–7, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20992 [ABSTRACT FROM AUTHOR]

A sudden capacity increase in demand during the summer peak, or in contingencies such as malfunctioning transformers, may cause an overload in normal transform-ers. In this paper, on the basis of overloaded transformer operation in distribution substations, thermal aging testing in oil was carried out under various overload patterns, such as short-term overload and long-term overload, but with the winding insulation paper's lifespan loss kept constant. From the results, various characteristics, such as the mean degree of polymerization and production of furfural and (C02+C0), and their effects on the lifespan loss of the insulation paper, were obtained. ©2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 1-8, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). [ABSTRACT FROM AUTHOR]

A model expressing beams, pillars, and electrical wiring in a building for lightning surge simulation by circuit analysis method is proposed in this paper. The proposed model expresses the self‐surge impedance of the electrical wiring as a function of the distance between conductors and the radius of the electrical wiring. The mutual impedance is expressed by the distance between the surfaces of a structure and a nearby wire instead of the distance between the conductor centers. In the case of two conductors having far different radii in proximity, the distribution of electromagnetic fields around the two conductors is similar in horizontal and vertical arrangements. Thus, the electrical wiring nearby pillars can be treated as a horizontal conductor. The circuit analysis results show that the voltage difference generated between the structure and the electrical wiring is calculated more precisely by the proposed model than by the conventional model. [ABSTRACT FROM AUTHOR]

In this paper, we measured the electrical potential distribution of surface dielectric barrier discharges (SDBD) caused by alternating voltage in synthetic air and nitrogen using the Pockels effect. It was shown that different potential distributions of filament thickness and length are generated in synthetic air and nitrogen. A filament analysis based on mathematical morphology was performed to quantify the geometric characteristics of the filaments produced in each gas atmosphere. The results show that the discharge filament thickness and the entropy in the filament direction depend on the oxygen ratio and the magnitude of the applied voltage. [ABSTRACT FROM AUTHOR]

Permanent magnet synchronous motors (PMSM) are very popular in the industrial market. Recently, robots are installed to compensate for the shortage of labor. Due to the increase in motors, the number of power lines and position sensor cable wiring are increased; this increase in complicated wiring is a problem. As a method to solve these problems, power superimposition technology in the power line of a PMSM is expected to reduce the distribution cables. In this paper, the power superposition technology method, and circuit equations of mounting transformers in power lines are presented and are then verified by experiment, simulation, and linear analysis. The circuit equation is proposed as a three‐phase circuit equation, which is transformed into a dq‐circuit equation by a transformation matrix. The characteristics of the electric angular frequency versus the dq‐axis voltage demonstrated satisfactory results, with errors within 1% in linear analysis and simulation. The linear analysis and experiment are shown to be similar, although there are some errors. The validity of the circuit equations could be demonstrated by the verification results. [ABSTRACT FROM AUTHOR]

This paper describes the observed position dependent emission spectrum and vacuum ultraviolet (VUV) to clarify the optical structure of argon atmospheric pressure plasma jets (APJs). Visible emission spectra of argon, nitrogen, and OH molecules were measured as a function of position from the nozzle of plasma jet generator to gas flow direction. From the results, we realized that a certain electric field is required for producing high energy excited atoms of argon in the jet from the high voltage electrode in the device to the ground positioned at downstream side. Moreover, VUV was detected along the plasma jet through the downstream direction. Thus, we could picture that the light pattern of plasma jet of which intensity weaken depend to the distance from the nozzle is sustained by the above two factors with the present steady state experiments. [ABSTRACT FROM AUTHOR]

Since a motor drive system contains an inverter (high‐voltage circuit) and gate drive circuits (low‐voltage circit) with a switching regulator, electromagnetic noise is generated in each of these two circuits, and noise interference between these circuits can occur. This paper discusses noise interference between the high‐ and low‐voltage circuits of an electric compressor system with an integrated mechanical and electrical structure. Analysis using LTspice shows that the experimental and analytical results are in good agreement when a very small stray capacitance occurs between the high‐ and low‐voltage circuits. An experiment using an actual compressor showed that conducted noise above 20 MHz can be reduced by up to 10 dB by reducing the effect of stray capacitance between these circuits. [ABSTRACT FROM AUTHOR]

This paper addresses semiconductor piezoresistive materials selection in MEMS engineering design. From the practical engineering point of view, it is important to understand piezoresistance properties of semiconductors even if less accuracy under feasibility design phase. However, piezoresistance is frequently analyzed based on first principle electronic band structure simulations by sophisticate physicists. Practical engineers not familiar with this simulation cannot directly apply useful information derived from the result of simulation. This paper provides practical prediction method for piezoresistance based on electronic band parameters obtained from the state‐of‐the‐art solid‐state physics. It is demonstrated that the crucial parameters which control the p‐type shear piezoresistance coefficient π44 in diamond and zinc‐blend single crystals are the inverse of square of bond length in unit cell atom, the square root of valence light hole mass, and the shear elastic compliance coefficient S44. [ABSTRACT FROM AUTHOR]

Power capacitors are highly reliable due to their completely enclosed configuration. They are relatively trouble-free over the long term. However, their dielectric strength can be reduced due to some stresses, including overvoltage application or thermal degradation of the insulation material during long periods of operation; these events can result in dielectric breakdown of capacitors in extreme cases. Since almost all power capacitors with oil-impregnated paper have been operated for more than twenty years, some kind of failure should be expected. To prevent these incipient accidents, it is important to examine the insulation deterioration mechanism and evaluate the degree of deterioration before capacitor breakdown. To establish a diagnostic method of deterioration of the capacitors with oil-impregnated paper, we have conducted thermally and electrically accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results we obtained, it can be concluded that the behavior of the oil-dissolved gases can be used as a useful index to diagnose the insulator deterioration of these capacitors. [ABSTRACT FROM AUTHOR]

Though it is said that the paperless age arrived with the spread of personal computers, the amount of office paper used shows no tendency to decrease. In general, used paper is recovered and recycled in order to preserve the environment. But labor and expense are required for the recovery of used paper and the recycled paper is lower in quality. If we could reuse used paper repeatedly without these disadvantages, for example, by using copying machines that could print again by removing the toner on used paper, it would be very convenient and ecological. We therefore studied the removal of toner from used paper by the laser ablation technique. As an optical source, an SHG-YAG laser was chosen. The energy density of irradiation with an SHG-YAG laser for the removal of toner from used paper was examined. At an energy density of approximately 12 mJ/mm2, which was the average value, the toner was removed sufficiently to allow reuse of the paper. The conditions of the laser irradiation, specifically the laser scanning speed and the number of irradiations, were studied. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(1): 8-14, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21214 [ABSTRACT FROM AUTHOR]

In June 2001, the International Agency for Research on Cancer (IARC) classified ELF magnetic fields as a possible human carcinogen based on the results of two recent pooled analyses by Ahlbom et al. and Greenland et al. on epidemiological papers for childhood leukemia. Examining their data, this author read information other than theirs: in the paper by Ahlbom et al., for instance, 9 cases were prepared for verifying the hypothesis that magnetic fields are associated with childhood leukemia, and this author considers that the general conclusion derived by inductive inference is that the hypothesis is not supported, because 2 cases of the 9 support the hypothesis and 7 cases do not, although the hypothesis has been accepted by many people for about 20 years; furthermore, the author does not consider that the IARC's evaluation that risk doubles in excess of 3 or 4 mG is based on the general conclusion, because it is derived from pooling two kinds of data, one of which is the 7 cases bringing the “general conclusion,” and the other is the remaining 2 cases being the “particular fact.” © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 59–64, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10344 [ABSTRACT FROM AUTHOR]

In a multilayer insulator made of two or more materials with different dielectric constants and conductivities, internal space change accumulates at their interfaces. If the local field is increased by the accumulated charge, the electric durability of the insulator should be decreased. In this paper, we describe the space charge accumulation measured when oil-impregnated PPLP (polypropylene laminated paper), which consists of three layers, kraft paper, polypropylene (PP), and kraft paper, was subjected to a strong dc electric field. The experimental results suggest that internal space charge accumulates at both surfaces of a PP layer and that the electric field in the kraft paper layers disappears. © 1998 Scripta Technica, Electr Eng Jpn, 124(1): 1–6, 1998 [ABSTRACT FROM AUTHOR]

We show that a logical error is contained in some epidemiologic papers which intend to verify the hypothesis that there is an association between magnetic fields of power lines and childhood leukemia. For instance, the Swedish paper by Feychting and Ahlbom in 1993 presented a leukemia association related to calculated magnetic fields in one-family houses other than apartments, from the results obtained from stratified analyses according to type of building; this was contradictory to their premise that exposure assessment was calculated from magnetic fields irrespective of type of building. However, the authors stated in conclusion that their hypothesis could be verified, although it needed to be supplemented with other data, as was customary in epidemiologic analysis, in order not to miss any possible causes of cancer. Our views are as follows: Engineers in the field would be unlikely to accept any procedure that needs supplementary data, because it is employed at the author(s)'s will for the intended verification of the hypothesis; it would be natural to suppose that the hypothesis could not be verified. © 2000 Scripta Technica, Electr Eng Jpn, 134(3): 53–59, 2001 [ABSTRACT FROM AUTHOR]

The bushing of a transformer is one part of the transformer system, but is as vital as the transformer itself because it forms a part of the main circuit. Deterioration and abnormal condition of the bushing possibly cause its destruction, shortage of the main circuit to the Earth, and fire in the systems, so that diagnosis of the bushings is thus very important. At present, mainly visual inspection from outside of the bushing is carried out. Inspection of the inside condition of the bushing by dissolved gas analysis of the inside oil is done only as sampling for selected bushings because it is difficult due to the sealed construction of the bushings. Therefore, a simple diagnostic method for bushings has been expected for a long time. In Eastern Europe, the RVM (Return Voltage Measurement) method based on scanning the polarization spectra was applied to the oil–paper insulation systems inside the transformer as a diagnostic method. In this paper we investigate theoretically the principle of the RVM method applied to bushings with the same oil–paper insulation systems as the transformer by using the equivalent circuit, and the possibility of using this novel diagnostic method for condenser-type bushings is demonstrated by a model experiment. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 21–29, 2000 [ABSTRACT FROM AUTHOR]

The energy consumption of a battery‐powered train in an interstation depends on the running time and state of energy (SOE) at departure. In this paper, we develop an optimization method of train timetables to minimize energy consumption in line with several stations. The variables in this proposed optimization model are running, dwell, and charging times as real numbers and places of charging facilities as binaries. Additionally, we conducted a case study using the real‐world light rail transit (LRT) route, vehicle, and onboard battery model to confirm the effectiveness. In the case study, the proposed method can optimize the timetable and placement of charging facilities by considering the track gradient and battery SOE. [ABSTRACT FROM AUTHOR]

Bus bar of substations are important equipment where multiple facilities are centrally connected, and the impact of a fault is significant. Therefore, bus bar protection relays have unique functions to correctly detect the point of fault, which allows high speed fault elimination and minimization of outage area. This paper describes functions and roles of bus bar protection relays applied in distribution substation of Kansai Transmission and Distribution. After describing the concept of installation of bus bar protection relays, recent trends in device development tailored to the bus bar configurations of substations and the unique functions of bus bar protection relays are introduced. The retrofit methods that are being increasingly applied as a renewal solution for bus bar protection relays are then described, as well as prospects for bus bar protection functions in the future IEC 61850 full‐digital substations. [ABSTRACT FROM AUTHOR]

A linear motor that uses a finite length Halbach array as its magnetic field causes a thrust force ripple owing to end effects. In this paper, the theoretical and numerical analysis methods of the Halbach array are investigated. The results of the electromagnetic field analysis are compared to confirm the validity of the theoretical and numerical solutions. Moreover, we focus on the magnetic pole period and coil arrangement of the finite length Halbach field type linear motor to eliminate the influence of the end effects, and report the relationship with the end effects. [ABSTRACT FROM AUTHOR]

In this paper, a streamline display method for magnetic flux density and magnetic field strength vectors in a three‐phase induction motor model core is presented, and the relationship between streamlines and magnetic properties is investigated. It is possible to visualize the vector magnetic properties distribution by representing the magnetic flux density and the magnetic field strength vector with the streamlines. In addition, the time variation of the streamlines of the magnetic flux density and magnetic field strength vectors, and magnetic energy was compared. It was clear that the magnetic energy did not necessarily increase in the areas where the magnetic flux density and magnetic field strength increased because these vectors have the spatial phase difference. [ABSTRACT FROM AUTHOR]

Power capacitors are highly reliable equipment due to their completely enclosed configuration. They have usually worked with very little trouble for a long time. Their dielectric strength can, however, be reduced due to some stresses such as overvoltage application or thermal degradation of the insulation material during their long period of operation, and these events can result in the dielectric breakdown of the capacitors in extreme cases. Power capacitors with oil-impregnated paper/film are commonly used in substation. Therefore, it is very important to diagnose the deterioration and predict the remaining service life of such equipment, to assist in plant maintenance. To establish the diagnostic method of the deterioration of the capacitors with oil-impregnated paper/film, we have conducted thermally and electrically accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results obtained, it can be concluded that the behavior of the oil-dissolved gases can be used as a useful index to diagnose the insulation deterioration of these capacitors. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(2): 1–9, 1997 [ABSTRACT FROM AUTHOR]

Power transformers have been expected to work with safety and reliability over a period of more than 30 years. The life expectancy of transformers depends upon the degree of deterioration of insulating materials, particularly conductor insulating paper. Many attempts have bee made in recent years to estimate the degree of deterioration of transformers but no diagnostic techniques have been put into practical use because of the difficulty of taking into account the service conditions. It is well known that materials change color when they deteriorate, but no colorimetry study has been made on material deteriorations. According to the recent advances in instrumentation and data processing equipment, the color of materials has become easy to measure qualitatively. Therefore, the basic investigation on colorimetry of insulating papers has been made to clarify the applicability to power transformers. Test results showed a strong correlation between the color difference and the deterioration of insulating paper. This report discusses the effect of materials of papers and impregnating oils on colorimetry. [ABSTRACT FROM AUTHOR]

The Swedish (Karolinska Institute) epidemiology investigation, which has been carried out on cancers in children residing near high-voltage power lines in and outside Stockholm county during 1960 to 1985, makes the conclusion that there is a significant association between the historical magnetic fields calculated and childhood leukemia. Employing the results of the stratum-specific analyses, and assuming that the relative risk of childhood leukemia is significant whenever the lower limit of its 95% confidence interval is above unity, we learn that the association is seen for children diagnosed during 1975 to 1985 residing outside Stockholm county, while it is not seen for those diagnosed 1960–1974 residing in and outside Stockholm county. We thus conclude that the association is not a causal relation, because consistency of association was not always seen throughout the areas and periods investigated. Therefore, we have no alternative but to consider that the conclusion which suggests that the same association is to be observed in every area and during every period is not valid. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 39–44, 1999 [ABSTRACT FROM AUTHOR]

The paper is proposed approximate formulas of the ac resistance of lead wires and coils which made by using copper clad aluminum (CCA) wires. There are the frequency range that the ac resistance of CCA wires is lower than it of cupper solid wires for lead wires and coils of an electrical equipment. It is shown that the application of CCA wires is economical as comparing with copper solid wires, if the design is due to successful calculation in the electrical equipment. The measured resistance is compared with the formula. CCA wires is an example of multiple conductors which shall be expected to apply in future. [ABSTRACT FROM AUTHOR]

The service restoration to sound sections within a short period as much as possible, performed after the permanent fault occurs in a distribution system, is significant for maintaining power supply reliability. This paper proposes an efficient method to find service restoration procedures based on fault searching and the optimal work scheduling of crews, considering the power supply priorities of loads and the probability of occurrence of faults. The proposed method is composed of two‐stage problems to reduce the outage sections efficiently: (i) the problem to find a series of searching procedures for unknown fault locations in the first stage and (ii) the optimization problem of work schedules of crews in the second stage. In the first stage, the order of operation of switches opened for searching for the fault direction is determined, constituting the searching tree. After that, the proposed optimization method can efficiently solve the work scheduling problem by formulating it as a mixed‐integer linear programming problem in the second stage. The computational experiments using a large‐scale distribution system model with many remote and manual switches show that the proposed method can provide efficient service restoration procedures within a reasonable computational time. [ABSTRACT FROM AUTHOR]

We are developing a small and lightweight direct‐drive system toward the realization of in‐wheel electric vehicles (EVs). To increase the power density of the motor, we developed a direct‐cooling motor that immersed the core, coils, and magnets in cooling oil and improved cooling efficiency. Moreover, we performed measurements of frictional loss, measurement of pressure drop, and a continuous heat‐run test on the test bench. The results demonstrated that direct cooling is effective and continuous operation can be achieved. Additionally, it was found that the coil temperature can be controlled by the flow rate of the cooling oil. In this paper, we report on the concept of direct cooling and the measurement results. [ABSTRACT FROM AUTHOR]

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel—crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength. [ABSTRACT FROM AUTHOR]

Photovoltaics (PV) output prediction, which is indispensable for power system operation, can affects demand and supply adjustment adversely when large prediction error occurs. Thus, the reduction of large error as well as average error is required in PV power prediction. In 2019, the operation of the Meso‐scale Ensemble Prediction System (MEPS) of numerical weather prediction started from the JapanMeteorological Agency, and the amount of forecasting information would be potentially useful for the improvement of PV power prediction. However, very few studies on inputting multiple meteorological elements of the MEPS have been reported. In this paper, we newly develop the prediction model for an area day‐ahead PV power output composed of Just‐In‐Time Modeling (JIT Modeling) with multiple elements of theMEPS. The developed method achieves precise forecasts with low computational load by both selecting meteorological elements valid for improving prediction accuracy and adequately devising the structure of JIT Modeling. Some numerical examples demonstrating the effectiveness of the developed method are also presented. In particular, the proposed method reduces large error significantly. [ABSTRACT FROM AUTHOR]

A novel high step‐up DC‐DC converter suitable for the power interface of fuel cells (FC) is presented in this paper. The proposed converter features a multi‐resonant tank for achieving high‐step up ratio under zero current soft switching (ZCS) without any snubber circuits. The simple and minimized‐component topology is beneficial for megahertz driving of gallium nitride (GaN) power transistors with effective reductions of switching loss, electromagnetic emission interference (EMI) noise, and ripple‐free DC input current. Mode‐transitional power stages are described in detail, following that the high step‐up principle is revealed by means of frequency‐domain analysis. The essential performances of the proposed circuit topology are demonstrated by simulation and experiment of 1.8 MHz‐120W prototype whereby effectiveness of the snubberless and multi‐resonant topology are verified from the practical point of view. [ABSTRACT FROM AUTHOR]

A multiphase DC‐DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high‐power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC‐DC converter that hardly lowers the power density. [ABSTRACT FROM AUTHOR]

This paper proposes a self‐conducting current bypass circuit for series‐connected diodes in high power semiconductor light source. This circuit enables the main circuit current flow continuously, even if several of the diodes connected in series are open because of breakdowns. Herein, the composition, operation, and circuit design method of the proposed circuit are described. Moreover, the development of a simulation model of the fuse, which is an element of the circuit, is described. Furthermore, the simulation result of the proposed circuit using the fuse model is presented, and the method of determining the circuit constant based on the simulation result is demonstrated. Finally, by connecting a prototype circuit based on this study in parallel with series‐connected diodes, we show that the main circuit current of 60 A flow continuously even when one of the diodes is open. [ABSTRACT FROM AUTHOR]

Electrochemical machining (ECM) is a processing method for metals that uses a DC power supply and flowing electrolyte. In some cases, discharge occurs during ECM when the gap between the electrode and workpiece, whose distance is rather small, is filled with hydrogen generated via electrolysis. We attempt to utilize a DC inductor placed between the DC supply and the ECM load in order to limit di/dt of the short or discharge current, which damages both the electrode and workpiece. When the output current surges, that is, when discharge occurs, the output voltage is suppressed by the DC inductance. In this paper, we propose a method for designing a PWM rectifier to reduce the discharge current, establish a linear approximation model for use in the PWM rectifier, describe a control method of the PWM rectifier, and demonstrate the efficacy of the model via simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes methodology and gate drive circuit that can immediately detect short‐circuit (SC) of multiparalleled SiC‐MOSFETs even under current imbalance condition. Proposed method detects SC current using an integration circuit that can sense di/dt. The detection level of SC current can be adjusted to a desired value regardless of the number of SiC‐MOSFETs connected in parallel. The effectiveness of the proposed approach was experimentally validated for four‐paralleled SiC‐MOSFETs under extreme current imbalance in SC condition. SC was detected within 0.5 μs and all SiC‐MOSFETs were protected without destruction at most 2.2 μs after the onset of SC, for all types of SC 1, 2, and 3. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission‐line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross‐section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission‐line constants of a conductor system in which both circular and rectangular cross‐section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

This paper proposes a new gradient driver with a gradational voltage inverter for low power loss and downsized filter circuits. Gradient drivers produce direct current with low ripple amplitudes to achieve high image quality and high slew rates to obtain images rapidly. The proposed gradient driver is characterized by low ripple amplitude of the output current from the inverter composed of SiC‐MOSFETs and high output voltage from another inverter composed of IGBTs. This paper discusses both the principle of operation and control method of the new gradient driver. Experimental verification is performed on a full‐scale system. The results show the advantages of the proposed gradient driver based on loss analysis by calculations. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission‐line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross‐section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission‐line constants of a conductor system in which both circular and rectangular cross‐section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

This paper proposes a new gradient driver with a gradational voltage inverter for low power loss and downsized filter circuits. Gradient drivers produce direct current with low ripple amplitudes to achieve high image quality and high slew rates to obtain images rapidly. The proposed gradient driver is characterized by low ripple amplitude of the output current from the inverter composed of SiC‐MOSFETs and high output voltage from another inverter composed of IGBTs. This paper discusses both the principle of operation and control method of the new gradient driver. Experimental verification is performed on a full‐scale system. The results show the advantages of the proposed gradient driver based on loss analysis by calculations. [ABSTRACT FROM AUTHOR]

In recent years, the aggregation business has gained a lot of attention in Japan. Aggregators will make contracts with customers with photovoltaic (PV) power systems and battery energy storage systems (BESSs) including electric vehicles (EVs) to participate in electricity markets. Aggregators might have to pay electricity supply‐demand imbalance charges when generated and consumed energies contracted at the day‐ahead supply‐demand market are different from those at the current day operation due to distribution network constraints such as voltage and power flow limitations. Therefore, the information on network constraints is very important for aggregators to determine their day‐ahead schedules. In this paper, we evaluated the relationship between aggregator supply‐demand schedules and the distribution system operation. It was assumed that the reverse power flow limitations due to network constraints are notified to the aggregators by distribution system operator (DSO). Two cases of the aggregators' schedules of PV systems and stationary BESSs were compared in the simulations. In addition, aggregator strategies for making adequate schedules were evaluated. [ABSTRACT FROM AUTHOR]

Recently, energy harvesting has attracted increasing attention. The present study focuses on vibration generators based on piezoelectric elements by proposing an internal capacitor cancel control (ICCC) rectifier to improve the output power. The proposed rectifier cancels the internal capacitor to improve the output power while retaining the maximum output power. Accordingly, this paper experimentally demonstrates the improvement in output power by using the ICCC rectifier compared to conventional circuits and the previous proposed circuit. [ABSTRACT FROM AUTHOR]

We are planning to develop the new Advanced Distribution Automation System (ADAS) equipped with optical communication network and sectionalizer with sensor for more grid reliability and efficiency on maintenance operation. The new system is featured with the function of fault cause or damaged part estimation. The new sectionalizer captures the waveform of electrical line surge originated by fault and the system analyzes the waveform for this function. This paper mainly introduces the system configuration of ADAS and an early stage examination of fault cause estimation technology. [ABSTRACT FROM AUTHOR]

This paper proposes the starting method for position sensorless controlled interior permanent magnet synchronous motors (IPMSMs) by using all-pass filters. The starting of IPMSM position sensorless control is well known to be extremely difficult due to the lack of electromotive information. Therefore, IPMSM is often started and accelerated with the high-frequency signal injection in general, and then, the control algorithm is switched to position sensorless control without high-frequency injection in middle speed region. However, the acoustic noise due to high-frequency signal injection would occur, and the switching of control methods would cause some bumps. For this reason, IPMSM is desirable to be driven from the start to the steady state without high-frequency signal injection. This paper realizes to start the position sensorless controlled IPMSM without high-frequency signal injection by allpass filter with the assistance of the appropriate initial vector setting of each controller, under the assumption that the high-frequency signal injection is used only at standstill. Finally, this paper experimentally demonstrates the feasibility and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we have fabricated surface acoustic wave (SAW) devices with six sets of interdigital transducers (IDTs) on half‐inch wafers of quartz with deposited thin films of aluminum nitride (AlN). Firstly, AlN thin films have been deposited by reactive sputtering in Ar‐N2 gas mixture at 400°C with the high‐power impulse magnetron sputtering (HiPIMS) system which was developed for microfabrication process in the localized clean environment with half‐inch wafer (Minimal Fab). After that, IDTs of Al thin films have been prepared on the AlN thin films. The X‐ray diffraction (XRD) pattern of the AlN thin films shows that the AlN films have c‐axis (002) orientation. Furthermore, the frequency responses have been measured with four paired IDTs of the SAW devices, which were selected from six sets of IDTs as an input electrode and an output electrode. These results show device properties responding to the design of the IDTs and also suggest the potential of the fabricated SAW devices as the four‐paralleled frequency filter and/or sensing system. [ABSTRACT FROM AUTHOR]

High step‐up boost converters with large input current capacity are necessary for low‐voltage renewable energy sources, such as photovoltaic panels and fuel cells. Interleaved converters are a suitable topology for low‐voltage, large input current applications. Conventional interleaved converters, however, face a variety of challenges, such as the necessity of additional current control loops for active current balancing, increased voltage stress of semiconductors, and poor extendibility. In this paper, highly extendable interleaved high step‐up boost converters with a passive current balancing and reduced semiconductor voltage stresses are proposed. Current capacities and step‐up conversion ratios of the proposed converters can be arbitrarily enhanced by extending the number of phases and voltage multiplier (VM) stages, respectively. The experimental results of 500‐W prototypes demonstrated passive current balancing, reduced semiconductor voltage stresses, and enhanced step‐up conversion ratios. [ABSTRACT FROM AUTHOR]

Electric power generated by photovoltaic (PV) systems is generally unstable because of uncertain meteorological conditions. Stably maintaining the supply‐demand balance of power systems requires an accurate prediction of the performance of PV systems. Especially for predicting the performance of the PV systems containing modules with different electrical characteristics or installed in different angles, it is necessary to calculate the generated power of the system by combining the current‐voltage (I‐V) characteristics of each module in series and parallel. Therefore, an accurate method is required for estimating the I‐V characteristics in various meteorological conditions. In this paper, a simple modeling method of the I‐V characteristics for crystalline silicon PV modules is proposed. The I‐V characteristics can be simulated in a good accuracy for practical use based on a simplified equivalent circuit of PV modules and a temperature correction of the short‐circuit current, open‐circuit voltage, and the current and voltage at maximum power point. The validity of the proposed method is examined by comparing simulated and measured I‐V characteristics of a PV module. Furthermore, to demonstrate the effectiveness of the proposed modelling method, it was applied to simulating the power generation of a PV system containing modules installed in different angles. [ABSTRACT FROM AUTHOR]