Electrical Engineering in Japan最新文献

We propose the novel magnetic compensation method which is suitable to compensate gradient magnetic fields. The method is to be applied to a conventional large-scale, tri-axial active magnetic shielding system such as a spacecraft magnetic testing facility. The essences of this method are the adoption of compensation coils which have degrees of freedom in their coil orientations, and their installation position, which is chosen to have certain distances from the center of the shielding area. The method works with at least four compensation coils. In this research, we actually demonstrated the method with a scaled-down experiment. Disturbance magnetic field (B) at the target zone was suppressed from 21.33 nT to −1.54 nT and magnetic field uniformity (ΔB) within the test zone was improved from 2.3 nT to 0.015 nT. In terms of magnetic field gradient, improvement from over 4 nT/m to below 0.5 nT/m was achieved.

We have demonstrated a capacitively coupled Hall-type MHD generator using ECR plasma. To clarify the characteristics of the fabricated MHD generator, we measured the power generation characteristics as a function of magnetic field strength using a DC Hall-type MHD power generation experiment. The results showed that the output power decreased due to magnetic pressure at the higher magnetic field. However, the output power corresponded to the theoretical value at the lower magnetic field. An AC Hall-type MHD power generation experiment was conducted using an AC magnetic field. As a result, full-wave rectification voltage was observed as per theory. Finally, capacitively coupled Hall-type MHD power generation experiments were conducted, and full-wave rectified waveforms were observed as in AC Hall-type MHD power generation. These waveforms were similar to the output waveforms predicted from theory. These results show that the capacitively coupled Hall-type MHD generator is feasible.

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.

The effect of the secondary electron emission coefficient on accumulated charge density distributions in atmospheric pressure dielectric barrier discharges have been simulated using two-dimensional fluid model. Spatio-temporal distributions of accumulated charge density on each side of the dielectric have been examined. The differences of conventional waveforms of accumulated charge density and the simulated results were clarified. And when the dielectrics were negatively accumulated, charges were uniformly accumulated, while positive charges were not. Randomness of streamers' occurrence, and self-organized structures have been also examined by the accumulated charge distributions.

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.

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.

In recent years, the introduction of photovoltaic power generation systems has been increasing from the perspective of global warming countermeasures. However, there is a problem that it becomes difficult to adjust the supply and demand balance of electric power. Therefore, in this research, the inverter by using estimation signal estimates the load of the consumer, then we aim to adjust the supply-demand balance at the demand side. By the verification of experimental, three-phase inverter, which is assumed to be an industrial photovoltaic power generation system, estimates the load by using pseudo random binary sequence (PRBS) signal and two proposed methods. The load estimation results show that the error rate of the estimated resistance of each phase is within a few percent by using the two proposed methods, and the load estimation is achieved.

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.

The pulsed electroacoustic method determines the distribution of space charge in an insulation system by applying a pulse voltage and detecting the acoustic response. It estimates the location and magnitude of charges from time-domain signals. For quantitative analysis, a bias voltage is applied to a specimen with no space charge, and the acoustic signal generated from the electrodes only is used as a reference waveform for calibration. However, a full-scale, extra-high voltage insulation system often already contains space charges in it. Therefore, a method of acquiring a reference signal under such a condition was studied. We studied methods to compare voltage variations and response signal variations. We proposed a method that measures the signal difference at different voltages. In addition, we proposed a method of correlating voltage and signal variations that may allo for more rapid signal acquisition. The feasibility was proved using an 11 mm-thick mimic polyethylene specimen.

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.