ABSTRACT Rare‐earth transition‐metal alloy thin films, which serve as crucial test specimens for creating ultrafast spintronics devices, have major composition and temperature dependencies of magnetization based on the ferrimagnetic model. Although the thickness dependency of magnetization characteristics is known even in thin film regions, this dependence is difficult to explain conventional models. This study systematically evaluated this thickness dependence and confirmed an inverse proportional trend with film thickness for two compositions. Based on these results, we propose a new model involving sublattice magnetization networks with volume difference. Using this model, we confirmed significantly suppresses the thickness dependence of magnetization in GdFeCo films which adjacent Gd thin films. Furthermore, we verified the validity of the model through the response of the all‐optical magnetization switching phenomenon based on the sublattice magnetizations.
ABSTRACT For example, a semiconductor element is turned off in a power supply circuit. A part of the circuit becomes an open‐circuit. The magnetic energy stored by the parasitic inductance of the conductor line in the open‐circuit is then released as circulating currents flowing within the conductor line. The circulating current flows symmetrically between the left and right sides of the conductor line, which is divided into two parts widthwise. The author clarified this circulating current by measuring the local magnetic field on the conductor line using the optical probe type magnetic field sensor. In addition, this paper describes in detail the current density distribution and the magnetic field of the circulating current in conductor lines of various cross‐sectional shapes. The analysis results revealed that the integrated current density within the conductor line is zero regardless of the cross‐sectional shape of the conductor line, but circulating currents flow. Also the magnetic field around a highly symmetric cylindrical conductor line is zero. On the other hand, the magnetic field increases as the aspect ratio increases, as in the case of a less symmetrical rectangular conductor line.
ABSTRACT Three‐dimensional numerical analysis is conducted to clarify the effect of wavy Taylor vortices on the power generation characteristics of a co‐axial magnetohydrodynamic energy conversion device. The numerical results show that time‐periodic oscillations in the input and output powers occur when the load factor, which is defined as the ratio of the load voltage to the induced electromotive force, is below a threshold. These are caused by the modulation of the wavy Taylor vortices induced inside the device. Additionally, the oscillation amplitude of the output power is considerably small even when the oscillation amplitude of the input power is maximum. The effects of Taylor vortices and Lorentz force on the input power are also investigated. The dependence of the input power on the load factor is determined by the balance between the contribution from inertial force (convection), which increases with increasing load factor, and the contribution from the Lorentz force, which decreases with increasing load factor.
This paper handles a workforce re-planning problem when an unplanned urgent task occurs and proposes a method to reduce the total outage duration of the plan. Recently, many enterprises have been introducing Field Service Management (FSM) system. FSM supports enterprises to list on-site tasks, manage progress of them, and plan workforce schedule for more efficient and faster work. It is expected to be utilized for power companies because they also have many on-site tasks such as managing assets/vegetation, replacing/fixing grid elements, and removing faluts. On-site tasks in the filed of power grids often require a planned outage to ensure safety for filed workforces. Thus, when an falut occurs, they have to stop their service due to the additional unplanned outage. This paper focuses on the ineffciency and proposes a method to bundle unplanned and planned outage by bringing forward planned tasks to the unplanned outage duration. The method was tested in two cases and confirmed that it can reduce the total outage duration or increase the number of planned tasks by appropriately setting the urgent task deadline in input task list.
In some traction substations along the Tokaido Shinkansen, railway static power conditioners (RPCs) have been introduced to suppress power supply voltage fluctuations to levels at or below management limits, in order to meet the technical requirements stipulated in power supply agreements with electric utility companies. This paper describes the development of two control methods aimed to mitigate fluctuation effectively for minimization of RPCs’ capacity: (1) optimization of reactive power compensation control using an automatic voltage regulation, and (2) voltage fluctuation mitigation control for exchanging active power which utilizes RPC’s capacity effectively by enabling unbalanced operation even under light load conditions through offset settings.
ABSTRACT In April 2021, Japan implemented a balancing market to ensure more efficient and economical operation of control reserves. Since 2024, frequency containment reserves (FCRs) have been procured through this market. A committee of the Japanese Organization for Cross‐regional Coordination of Transmission Operators (OCCTO) is discussing cross‐border FCR procurement. Additionally, improving the resilience of the power system is necessary following the major blackout caused by the 2018 Hokkaido Eastern Iburi earthquake. To address these technical issues, we developed a simulation model for frequency analysis under emergency conditions. This model includes power plant models, renewable energy source models, load models, a frequency calculation model, tie‐line models and stabilizing control system models. We validated the simulation model by comparing its results with measured data on frequencies and tie‐line power flows.
Aiming to evaluate and compare the performance of Interior Permanent Magnet (IPM) motors in a wide frequency range extending from low to switching frequency bands, wide frequency band equivalent circuits were constructed for stator assemblies and IPM motors to evaluate their static state. These equivalent circuits were introduced by combining the electrical equivalent circuit derived from the magnetic circuit with that of the armature winding and magnetic cores. The impedance and the input power of the armature winding terminals were calculated based on the derived equivalent circuit, and the measurements were compared. The results clarified that the leakage inductance caused by the magnetomotive force due to iron loss should be considered, which is not considered in the excitation circuit of conventional equivalent circuits of transformers and induction machines, along with the impedance associated with the capacitance between the armature winding and stator core. In addition, the equivalent circuit of the rotor portion should consider the capacitance between the magnet and rotor core.
Simple and cost-effective methods for cavitation detection are essential for stable operation of water pump systems. This paper reviews the characteristics of motor current signals under cavitation conditions and propose a cavitation detection technique for inverter-driven pumps based on these signals. Experimental observations show that the spectral "foot" around the fundamental harmonic in the power spectral density (PSD) of the motor current signals increases during cavitation. Based on this observation, we define an evaluation value metric that quantifies this feature for cavitation detection.
In this paper, we proposed a method to judge the occurrence of approximately 6 Hz flicker caused by the islanding detection function equipped in PCSs connected to low voltage distribution systems. We compared the experimental results in a full-scale distribution facility with the judgment results and confirmed that the judgment accuracy was sufficient. Furthermore, we confirmed that a tool using this method can judge the occurrence of flickers on a distribution system scale within a period that is practical.
The paper deals with a series of improvements from design structure to testing techniques, including on-site testing for 550 kV gas-insulated busbar (GIB) using SF6 to improve the insulation reliability against metallic particles. The inner surface of the enclosure, unlike conventional designs, was dielectric-coated with a dielectric material to suppress the particle motions. The particle trap was upgraded from the conventional "slit type" to "opening hole type" at the bottom of the enclosure to ensure reliable capture of metallic particles and to prevent their re-movement. AE sensors mounted on the top of the enclosure enabled the detection of the accurate length and position of the particles. This technique allowed for confirmation via AE sensors that the particles were successfully captured in the improved particle trap. Finally, simple on-site conditioning tests became feasible by using system voltage instead of conventional stepwise-voltage-increase pattern, allowing for a simplified testing method without the use of testing transformers.
Catheter-based assessment and treatment of vascular stenosis are widely used. In this process, contrast media are commonly employed for accurate imaging diagnosis; however, the increased use of contrast media is associated with a higher risk of allergic reactions. In this study, we propose a method for identifying the site of vascular stenosis and evaluating treatment effectiveness using a catheter embedded with a fiber Bragg grating (FBG) sensor capable of measuring pressure differences, thereby reducing the reliance on contrast media. By simulating blood pressure distribution at the stenotic site, we confirmed that the pressure difference can be used to position the catheter accurately and assess treatment outcomes. Furthermore, we developed a prototype catheter with an embedded FBG sensor and demonstrated its pressure measurement capability in a fluid environment. Our analysis and experiments confirm that an FBG-embedded catheter can effectively identify vascular stenosis and quantify its severity.
Global warming and frequent heatwaves make the prevention of heat-related illness an urgent issue. To avoid dangerous heat stress, monitoring core body temperature, heart rate, and sweat loss is essential. Conventional methods rely on several separate sensors, which reduce practicality in daily life or field use. This study introduces a compact, wearable multimodal sensor probe that can simultaneously measure core body temperature, electrocardiogram (ECG), heart rate, and sweat rate. The device uses a heat flux-based unit to track both core body temperature and cardiac signals, while a computational model estimates sweat loss. Validation experiments were conducted with ten healthy men during cycling exercise in a controlled environment. The prototype achieved a root mean square error of 0.087 degrees C for core temperature and 131 g for total sweat loss, surpassing previous approaches. During exercise and recovery, values were slightly overestimated, likely due to increased sweating and skin blood flow affecting heat transfer. Despite these limits, the device provides a practical way to monitor multiple physiological signals in real time under heat stress. It shows promise for use in occupational, athletic, and everyday settings to help prevent heat illness.
A double-sided cooling (DSC) power semiconductor module embedded with a silicon insulated gate bipolar transistor (Si-IGBT) or silicon carbide metal-oxide-semiconductor field-effect transistor (SiC-MOSFET) was fabricated. Their heat dissipation distributions were compared, and the causes of the differences were analyzed. The thermal resistance of the indirect cooling DSC Si-IGBT module was 0.121K/W. It was better than the single-sided direct cooling module, which reported a thermal resistance of 0.139K/W. An indirect cooling DSC SiC-MOSFET module with dispersed placement for the same package exhibited an almost equivalent thermal resistance of 0.124K/W, despite possessing a smaller die heat dissipation area owing to its higher current density. Si-IGBT and SiC-MOSFET reported 37.1% and 29.7% of the heat flux share from the die to the upper surface, respectively. It was clarified that the share is determined by the ratio of the spacer area on the surface side to the die active area on the backside.
We have proposed a magneto-plasmonic system consisting of the [Pt/CoPt/Pt]/Ag stacked films for hydrogen sensing applications. The [Pt/CoPt/Pt] layer provides both the magneto-optical activities and hydrogen reactions. The sensor elements produced significantly hydrogen responses.
This paper reports on the improvement of a photovoltaic power conditioning system (PCS), which is one of the renewable energy sources, to a grid forming (GFM) control type, and the successful results obtained from laboratory tests conducted on a 20 kW apparatus. Because it is a voltage-controlled type, it always synchronizes with the AC system, including generators, through synchronizing power. This increases the short circuit capacity of the system and contributes to the suppression of voltage fluctuations. Additionally, having virtual-inertia characteristics and frequency droop characteristics enhances the inertia of the AC power system and contributes to the suppression of frequency fluctuations. With such features, it is expected that it will be one solution to the challenges of the power system that may concern the increase of renewable energy in the future.
Simple and cost-effective methods for air entrainment detection are required for the efficient maintenance of pump systems. Recently, motor current signature analysis (MCSA) has been gaining attention for motor fault detection. In this paper, we review the characteristics of motor current signals in an air entrainment state and propose an MCSA technique for air entrainment detection. We observed that the foot around the fundamental harmonic spectrum in the power spectral density of current signals increased with an air entrainment. Based on these results, we propose defining a characteristic value which reflects this feature.
This article presents a design methodology for low-voltage converters and an associated cooling structure necessary for applying a modular multilevel converter (MMC)-based active power filter (APF) using low-voltage Si-MOSFETs, specifically for inverter-driven air conditioners. The voltage detection circuit is simplified by referencing the MMC neutral point, eliminating voltage concentration on specific cells during APF shutdown. The proposed MMC-APF comprises 36 low-voltage Si-MOSFETs, each with an on-resistance of several m Omega, effectively distributing heat generation and limiting power loss to less than 1W per device. By utilizing airflow from the air conditioner's outdoor unit fan, the system operates without additional heatsinks or cooling fans. Experimental results confirm that the proposed MMC-APF achieves purely sinusoidal source currents with a unity power factor, while reducing total loss by 38.6% compared to a conventional two-level IGBT-based APF.
When output power from photovoltaic power generation system (PV system) to distribution system approaches the stability output limit, the power conditioning system (PCS) becomes uncontrollable. In this study, the stability output limit in the distribution system, where two PV systems are connected, were investigated. A numerical calculation method was developed to estimate the influence of the magnitude of output power and the connection location of PV systems on the stability output limit. It was assumed that a PV system (PV system1) is connected in the middle of the distribution line and the other one (PV system2) is connected to the end of that. In case that one PV system1 is con nected near the end of the distribution line, the stability output limit decreases with an increase in the output power. On the other hand, if the connection location of PV power1 is closer to a distribution substation, there are conditions under which the stability output limit increase with the output power. By calculating the stability output limit according to the actual the power distribution system conditions and setting the output power of PV system, it is possible to obtain the output power conditions for stable operation of PCS.
In this paper, bobbin coils are used as magnetic energy harvesting coils. Bobbin coils are low cost and have a high degree of freedom of shape. An equation is proposed to estimate the harvesting power of a magnetic energy harvesting coil from the mass and bobbin size of the bobbin coil. Electromagnetic induction experiments with the bobbin coil were carried out and the relative error to the harvesting power obtained confirms the agreement with the trend of the estimation equation.
To enable efficient vibration diagnosis of rotating machinery in industry settings, we investigate a spectral analysis approach for accurately estimating the envelope spectrum from short-duration vibration signals, thereby reducing data traffic. We propose the use of the maximum entropy method as the spectral estimation algorithm for short-record vibration data and demonstrate that it achieves significantly higher accuracy than the commonly used fast Fourier transform. Through analysis of both simulated and measured vibration data, we show that this approach can reduce the data required for vibration diagnosis to approximately one-tenth of that required by conventional methods.
