Electrical Engineering in Japan最新文献

One of the models for rotating machines, such as synchronous machines and induction machines, is the phase-domain model, which is characterized by formulating the circuit equations of the rotating machine in the phase domain and solving them simultaneously with the external system to which the rotating machine is connected. Although this model has excellent numerical stability and calculation accuracy, it requires refactorization of the subcircuit that includes the rotating machine at each calculation time step, which degrades the calculation speed. This paper describes the results of an attempt to improve the calculation speed when using the phase-domain model by using partial refactorization, which makes the refactorization process more efficient.

In recent years, a demand for smaller traction motors with higher power has arisen. This study focused on high-speed rotation for miniaturization and developed a prototype motor using Nd-based bonded magnets. It had a maximum rotational speed of 34,000 rpm, which is twice that of existing 50 kW-class motors. The motor achieved the desired performance in the test in combination with a reducer. As a result, the weight of the prototype motor was reduced by 54%, and a power density of 6.7 kW/kg was achieved.

Technical innovations for the downsizing of motor systems are necessary to realize energy savings and roomy and comfortable car interior space in electric vehicles. In this paper, a novel motor drive system with multiple high-speed motors and a magnetic multiple spur gear (MMSG) is proposed for electric vehicles. Furthermore, the factors leading to a high-power density and high torque density in an MMSG system are clarified.

This paper addresses drone controller design with 3D target trajectory and presents a backstepping-based controller taking into consideration the integral of tracking error. Performance evaluation is performed in situational and experimental environments, and the advantage of the proposed scheme is illustrated in the comparison with the conventional backstepping and the Proportional-Integral-Differential control. The experiment results show that the proposed scheme exploiting the integral of tracking error can reduce steady-state error. Furthermore, they show that introducing a reference model experimentally improves the tracking performance for a given target trajectory.

The paper presents a new fault location method with traveling waves (surge) on distribution line to restore power supply as soon as possible. The proposed method builds a diagram that describes transmission and reflection of traveling waves over the lines and generates pseudo waves based on the diagram. The least error condition including fault point is estimated by numerical analysis comparing measured waves and pseudo waves. The method is robust and accurate without line parameters such as the speed of traveling waves. The method can be applicable for multiple faults and branch line faults without any additional modification.

For the insulation diagnosis of stator windings of generators, sampling surveys are conducted on the coils to estimate the dielectric strength of the stator winding. Previous research has relied on inferring the breakdown voltage of the stator winding from the value 3σ away from the mean value of the breakdown voltage of the coil. However, this conventional method exhibits a significant estimation error when the sample size is small. Therefore, we propose a method for estimating the breakdown voltage of the stator winding based on the maximum value of the partial discharge magnitude and the minimum value of the breakdown voltage of the sample coil. We verify this method by Monte Carlo simulation assuming a sampling survey of coils.

Nanosecond pulse electric field (nsPEF) therapy has attracted attention in recent years as a noninvasive cancer treatment with minimal side effects. However, the relationship between the electrical stress induced in cells by the external electric field and the biological response has not been fully investigated quantitatively. We investigated the effects of nsPEF therapy on cancer cells using microgap electrodes under low-voltage conditions. We developed an equivalent circuit model using intracellular components to determine the amount of stimulation of cellular components and performed frequency analysis of nsPEF. nsPEF applied to Jurkat cells activated caspase-3 and induced apoptosis at shorter pulse widths. nsPEF induced biological responses and apoptosis in cancer cells. The relationship between the biological response induced by nsPEF and the amount of electrical stimulation was investigated by comparing the experimental results with frequency analysis. Using quantitative values for each cellular element, the relationship between the biological response and the amount of electrical stimulation can be integrated.

In this study, we explore an innovative method for iodine oxidation utilizing ozone generated through plasma phenomena.  Our investigation centers on understanding the amount of oxidation by ozone in an Aqueous Solution, quantifying it with that of an aqueous potassium iodide solution, thereby assessing the viability of our proposed technique. While certain practical considerations warrant attention as we strive for real-world implementation, we posit that elevating ozone production by expanding the electrode discharge area holds promise for further optimization and subsequent cost minimization.

In this study, silver nanowire covered with graphene (AgNW/Graphene) transparent conducting electrodes (TCE) were developed as bendable TCE instead of conventionally used indium tin oxide (ITO) for flexible photovoltaic applications. CVD-grown graphene films were transferred from a Cu foil onto a spin-coated AgNW TCE. AgNW/Graphene TCE exhibited lower electrical resistance than 10 Ω and high optical transmission of approximately 80% at visible wavelengths before and after bending of 20 cycles at a radius of 15 mm. Thermal tolerance of AgNW was drastically improved by protecting silver nanowires with graphene from oxidation at the 300°C air annealing test. ZnMgO/Se thin film photovoltaic devices with AgNW/graphene were successfully demonstrated by insertion of a sol-gel ZnO buffer layer in order to protect AgNW/graphene from sputtering bombardment.

It is important to drive an IPM motor system stably. However, unstable oscillations at the DC input have been reported. According to the impedance method, stability is assured when the input admittance of the drive system is passive or resistive. In this paper, we propose a passive admittance control method utilizing a Lyapunov-based method. The control principle is first described and then a design example is detailed. It is shown that the proposed method achieves passive frequency characteristics for the input admittance. Its stable operation behaviors were investigated both by simulation and experimentally.