Electrical Engineering in Japan最新文献

Despite ensuring the integrity of bogie frames for railway vehicles via nondestructive inspections during periodic maintenance, the possibility of fatigue cracks occurring at locations other than the predetermined inspection points cannot be dismissed. Therefore, fatigue cracks can be prevented more efficiently by assessing the overall degree of fatigue damage to the entire bogie frame and determining the results via nondestructive inspections. In this study, dynamic stresses in the bogie frame during running were estimated via finite element dynamic analysis by using the axle box acceleration as input, and the degree of fatigue damage and life were calculated from the waveform of the estimated stresses. Furthermore, we developed a bogie frame fatigue prediction system based on a high-speed and high-precision stress calculation method. The developed system visualized the overall relative life.

The axial gap structure of a half-wave rectified variable field flux motor (AG-HVFM) has been proposed, which has a double stator structure and field winding short-circuited by a diode. Although the AG-HVFM can achieve a high-efficiency drive in wide speed and torque range via variable field flux control, its structure deteriorates the average torque and torque ripple. In this paper, we sequentially design the core shape, aspect ratio, and current control method for an AG-HVFM to improve its torque characteristics.

Recent methods using thermistors as an early detection of skin cancer require the higher resolution of 5 mK. Previously, the authors developed a vacuum insulated temperature device that calibrates the resistance temperature characteristics of thermistors, so that it improves the temperature resolution and accuracy of skin cancer diagnosis. In this study, the operational methods of the calibration system were compared for improving further accuracy using the temperature calibration device and the oil tank calibration device. The results of the comparison indicated that the temperature calibration device is probably as accurate as the oil tank calibration device.

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.

We investigated AC breakdown characteristics of ultra violet curable epoxy resin (UV-EP) with nitrogen fine bubbles (FBs) in order to improve insulating properties of UV-EP. As a result, it was found that self-made FB generator mainly add FBs with a diameter between 60 and 150 nm to FB-EP before curing. In addition, SEM images revealed that FB-EP has FBs after curing. Bubble diameter in FB-EP after curing was estimated between 55 and 140 nm due to resin shrinkage. Furthermore, partial discharge inception voltage and electric strength of FB-EP with FB addition for 10 min were almost the same as No FB-EP.

As one of NEDO's international demonstration projects, a large-capacity hybrid battery storage system which consists of two types of battery cells with different charge-discharge characteristics was constructed in the state of Lower Saxony in the Federal Republic of Germany. By using the hybrid battery system has a lithium-ion which has an advantage in short time and high rate, and a sodium-sulfur battery (NAS) which has an advantage in long time and low rate, the tender participation in the balancing power market in Germany had been executed. The hybrid battery storage system could successfully drive and provided services for primary and secondary control reserves, elimination of power imbalance, and reactive power injection, as well as a combination of these services.

Electrification is progressing across different fields such as automobiles and construction machinery. Motors for electric systems are required to be compact and achieve high power density. In this study, we developed a small motor with rotation speed of 22,000 r/min by reducing stress concentration. Each pole has three magnets in the circumferential direction, and the magnets are arranged in a U-shape. The magnet insert slots are comprised of expanded flux barriers on the inner diameter side and a guide-less structure. The magnet slots reduce stress concentration. Additionally, the rotor has two dents on the outer diameter surface and expanded flux barriers on the outer diameter side. The dents have different shapes between the North (N) and South (S) poles. The structures reduce the torque ripple.

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.

In order to achieve net-zero carbon emissions by introducing enormous amount of renewable energy, it is essential to secure the reserve power to improve the power quality of the grid. On the other hand, improvement of the grid resiliency is also needed in case of emergency such as outage of the grid. The energy storage system can be the solution for both of securing the reserve power and improving grid resiliency. The authors have conducted demonstration project to validate the applicability of Redox Flow (RF) battery for securing the reserve power and improving grid resiliency. The results of the demonstration validated that the RF battery makes it possible to be used as reserve power and earn revenue through energy and ancillary market transactions during normal operations, in addition to providing power to blackout areas or the areas that outages are assumed, as an independent power source, during an emergency such as natural disasters and planned outages.

Conventional methods to schedule power generators maintenance aim to secure enough supply reserve margin to the power system when its power generators have to go under maintenance. However, the use of such methods in scenarios of large penetration of VRE, might be problematic. This is because in such scenarios conventional scheduling methods might inadvertently concentrate maintenance operations when residual demand is particularly low, creating situations in which there is insufficient supply-demand balancing capability and inertia to operate the power system properly. In this study, we present the development of a new method to schedule generator maintenance that ensure inertia and balancing capability constraints, and show its effectiveness.