Electrical Engineering in Japan最新文献

In critical mode power factor correction (PFC), the switching frequency is varied to achieve a sinusoidal input current waveform. Under certain conditions, a higher frequency increases the loss and noise. Meanwhile, the limitation of the switching frequency leads to an increase in input current distortion. This paper proposes a method to prevent an increase in distortion by compensating the pulse width at a limited frequency. Using this control method, critical mode PFC with a limited maximum switching frequency was evaluated. As a result, the total harmonic distortion of the input current was lower than that before the frequency limitation. Furthermore, the improvement in efficiency and the reduction in conducted EMI were confirmed.

This paper proposes a new method for input current control of power factor correction (PFC) with continuous conduction mode (CCM), which does not require input voltage detection. As a control method that does not use input voltage detection, pulse width modulation (PWM) with the inductor current as the modulated signal is already in practical use however, this approach has limitations for the range of inductance values used. In CCM-PFC, the input rectified voltage and low-frequency component of the voltage of the switching circuit are approximately equal in the stable state as well as proportional to the PWM signal. This study uses the previous modulated signal as the estimated voltage value to generate an instantaneous current command for feedback control. In addition, a method to suppress the influence of the DC voltage ripple by changing the voltage control gain according to the value of the DC voltage was employed. From the evaluation, it was confirmed that the harmonics of the input current were suppressed within the specified range of values.

We have developed a MEMS Rogowski coil current sensor with spiral return coil. The Rogowski coil is formed on a silicon substrate clockwise and counterclockwise from the edges, for current detection and external magnetic noise compensation (device size 10 × 10 × 0.3 mm³, spiral coil 135 turns, via diameter 100 μm). When the slew rate (di/dt) was kept constant at 10 A/μs, and the current was changed by 5 A up to 40 A, MEMS Rogowski coil could detect current linearly. When the slew rate was changed by 10 A/μs up to 100 A/μs, it was found that the MEMS Rogowski coil could detect current almost linearly following the reference sensor. Hence, external noise compensation by the return coil has been confirmed.

The conventional electrolarynx (EL) restores the voice of people who have lost their voice, however, its voice sounds like a robot and it occupies user's one hand. Therefore, we developed a hands-free wearable electrolarynx that improves the voice quality with the LPC residual wave as the vibration sound. Our device was able to reproduce sounds below 500 Hz, which is close to the fundamental frequency, but from 1700 Hz to 4000 Hz, the conventional EL continuously showed a frequency response closer to the spectrum of the user's vocal sound than our device. Thus, the periodic sound of the fundamental frequency band was found to be closer to human speech than individuality or sound quality.

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.

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.

The high-thrust linear motor with a lightweight and high-strength mover was developed for operating circuit breakers. The linear motor is composed of a lightweight mover that has permanent magnets sandwiched between magnetic poles and an armature with a three-dimensional magnetic circuit. The specifications and performance of the linear motor were determined to cut off current soundly. Then, a prototype of a fully electrically operated breaker using linear motor was investigated. The linear-motor-based operating mechanism designed for the circuit breaker reached the open-pole position in 13.2 ms from the start of movement. However, the time from opening to 0.5 cycle was 9.0 ms. In addition, the variation in breaking operation time was within 1 ms, which was expected that stable controlled operation.

This study investigated cost-effective energy strategies for realizing net zero CO₂ emissions in Japan by 2050, employing an energy system optimization model with hourly electricity balances. The detailed temporal resolution enables the model to capture the intermittency of variable renewable energy (VRE) and the costs of system integration measures. Siting constraints on VRE, such as prohibiting solar PV and onshore wind developments in forests and offshore wind developments inside fishery rights areas, are incorporated in the model to reflect the environmental protection and social acceptance perspectives. Simulation results imply that a well-balanced power generation mix, combining renewables, nuclear, gas-fired with carbon capture and storage, as well as ammonia-fired, would contribute to curbing mitigation costs. In contrast, a simulation case with very high VRE penetration poses economic challenges. The average shadow price of electricity in 2050 in a 100% renewables case (RE100) is projected to be more than doubled from a reference case which is based on middle-of-the-road assumptions. Marginal CO₂ abatement cost in 2050 increases from 49,200 JPY/tCO₂ in the reference case to 75,300 JPY/tCO₂ in the RE100 case. The economic viability of high VRE penetration is improved by relaxing the siting constraints, although it may raise environmental and social concerns.

In this paper, a calculation method is proposed for the radial suspension force of a bearingless motor with a surface-mounted permanent magnet (SPM) rotor, a consequent-pole permanent magnet (CPM) rotor, and a homopolar permanent rotor (HPM). The radial suspension forces are calculated mathematically and analytically using the airgap flux density. It was confirmed that the proposed radial force equations are practical to calculate the suspension force based on the airgap flux density. The CPM bearingless motor and bearingless AC HPM have salient pole rotors that interact with the 2-pole Magnetomotive force (MMF) to generate 6- and 10-pole components. As a result, the radial suspension force of the CPM bearingless motor is generated by 8- and 6-pole, and 8- and 10-pole magnetic flux, whereas the bearingless AC HPM produces the radial suspension force by DC and 2-pole components. The shaft torque, the suspension force, and efficiency were also compared for SPM, CPM bearingless motors, and bearingless AC HPM. Consequently, the torque value of the CPM bearingless motor is quite close to SPM bearingless motor. Moreover, the suspension force of the CPM bearingless motor is quite close to bearingless AC HPM.

In order to improve the mileage per charge of battery electric vehicles (BEV), dynamic wireless power transfer systems are being developed. There are some problems such as is the wide gap between coils when mounted under the floor of a vehicle, and the effect of foreign objects between coils on power transmission. In-wheel coils, in which the coils are placed inside the wheel, have been proposed as a solution to these problems. However, they a plastic wheel such as CFRP and cannot reduce the gap between coils. In this paper, we propose a coil configuration in which the coils are placed inside the tire and the wheel. This configuration has the advantage of using a conventional aluminum to reduce the gap between coils. The effectiveness of this method is demonstrated via simulations and experiments.