Electrical Engineering in Japan最新文献

A sensory test experiment (triangle difference test) was conducted using the 20-component olfactory display to confirm odor reproduction based on odor components. The essential oils used were lemon, palmarosa, carrot seed, elemi, lavender, cypress and mentha arvensis. Each one was selected from seven essential oil categories. The sensory test reveals that it was difficult to distinguish between the reproduced odor and the target one. Thus, the odor reproduction by olfactory display based on odor components was generally possible. Furthermore, we found that the participants used its features or intensities as clues to distinguish between the blended odor and the target one from a survey of the free comments on the questionnaire sheets.

Conventional synchronous generators have been replaced by renewable energy source such as photovoltaics generation and wind turbine generation interconnected through inverters. As the capacity of synchronous generators interconnected to the power system decrease, the power system stability can be gradually jeopardized. Therefore, these inverters may be required to have some control functions in grid-interconnection code to support power system stabilization. On the other hand, it is known that the response of some control functions become unstable and undesired oscillatory behavior appears depending on the power system conditions such as low short circuit ratio. In consequence, not only the expected power system stabilization is not obtained, but also the power quality may be degraded. In this paper, the mechanism of these instabilities is clarified by using a simplified root mean square model, and a damping controller applicable to grid-following (GFL) inverter is developed. It is shown that the damping of the oscillatory behavior could be improved by applying the proposed controller using eigenvalue analysis and time domain simulation. This contribution is useful for the appropriate operation of the control function installed to GFL inverter.

A diode-clamped linear amplifier (DCLA) is proposed to realize low electromagnetic interference (EMI) caused by switching operations. A new concept of the DCLA, namely the higher efficiency unequally divided voltage power supply DCLA (DCLA-UeDV), is proposed. In previous studies, the optimal voltage ratio was derived, and a 1.7% points improvement in efficiency was realized for a rated unity power factor load. However, it has not been examined whether the conversion efficiency can be improved, except during the rated operation. In this study, operation of the DCLA is analyzed for changes in the amplitude of the output voltage and load power factor. Then, the advantageous operating region of the DCLA-UeDV against DCLA-eDV is clarified.

Transformers are normally energized from the higher voltage winding. In power system restoration, however, they may be energized from the lower voltage winding. Therefore, a reversible transformer model that is able to accurately calculate inrush currents and some other low-frequency transients is required regardless of which winding is energized. Although a reversible transformer model based on a topology-based model that considers magnetic couplings between phases has been proposed, it is difficult to determine the parameters of the model because iron-core and winding design information are not available in most cases. In addition, the approximation of the design information required when such information is not available does not always hold accurately. In this article, a reversible transformer model that can be composed only from available information such as nameplates and test reports, without using the design information (or the approximation), by using mutually coupled magnetic resistances has been developed. As a result of verification using a 500 VA single-phase three-winding transformer, it is indicated that the inrush currents calculated by the developed model are in good agreement with those obtained by the laboratory measurements using the test transformer regardless of which winding is energized.

Stabilization of resistive wall modes (RWMs) is one of the important issues in magnetic fusion research. In the reversed field pinch (RFP), the number of unstable RWMs becomes smaller by lowering the aspect ratio (A), the ratio of the minor to major radius of the device. In REversed field pinch of Low-Aspect ratio eXperiment (RELAX), whose aspect ratio is 2, unstable m/n = 1/2 RWM was stabilized by a single mode control power supply system with improvements of discharge performance. In this paper we report new results with modified power supply system in which magnetic boundary condition near the poloidal gaps is controlled. The modified power supply system is designed to stabilize the most unstable m/n = 1/2 mode by use of the saddle coil array covering the whole torus with eight (8) power supplies. The results show that the discharge duration is improved from ~ 3.0 ms to ~ 4.0 ms, limited by the capability of the iron core in RELAX device. Stabilization of the dominant RWM with the resultant improved plasma performance by a single mode control power supply system shows one of the advantages of a low-aspect-ratio RFP concepts.

Characteristics of ignition process of polymer-ablated arc with different current values were investigated with electromagnetic thermofluid analysis. This thermofluid simulation is based on calculated particle composition, thermodynamic and transport properties of evaporated vapor of polymer material and electrode material. Polymer ablation was assumed to occur by heat flux from the arc plasma. The initiation of polymer ablation was studied for different polymer materials because polymer ablation can affect arc behavior and then arc interruption ability. Results showed that it took time of milli- to tens milliseconds to initiate polymer ablation, and that its initiation time decreases with increasing current.

The electric railway is an environment-friendly transportation system. An energy-saving operation with a low cost and high energy-saving efficiency is often considered to further decrease energy consumption. An Automatic Train Operation (ATO) system has the advantage of energy-saving because a train can be controlled by an on-board computer. However, many railway lines are still being operated by drivers and controlled via manual operation in addition, energy managements often become difficult for drivers and operators. Therefore, a study of energy-saving manual operation is desired. Energy verification of a manual operation is difficult because an adequate experiment has several constraints and trial periods are limited. Moreover, it requires a considerable amount of time and effort. In this study, an energy evaluation system is developed to calculate the energy consumed by a train when a driver manually operates it through adding an advanced calculation device to a conventional railway simulator. Consequently, the evaluation system contributes to carry out simple experiments with a short duration.

Accurately calculating the transmission-line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross-section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission-line constants of a conductor system in which both circular and rectangular cross-section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results.

This paper proposes a new gradient driver with a gradational voltage inverter for low power loss and downsized filter circuits. Gradient drivers produce direct current with low ripple amplitudes to achieve high image quality and high slew rates to obtain images rapidly. The proposed gradient driver is characterized by low ripple amplitude of the output current from the inverter composed of SiC-MOSFETs and high output voltage from another inverter composed of IGBTs. This paper discusses both the principle of operation and control method of the new gradient driver. Experimental verification is performed on a full-scale system. The results show the advantages of the proposed gradient driver based on loss analysis by calculations.

Contact-force control of propeller-driven systems achieves aerial tasks that require contact motions with objects. Conventional contact-force controllers for propeller-driven systems utilize a contact-force feedback controller. Although the feedback gain should be high to achieve high target tracking performance, a high gain causes a large overshoot. This paper therefore proposes a novel contact-force controller which utilizes an airframe's velocity and an airframe's acceleration. An estimated acceleration and an estimated velocity of the airframe are fed back to the contact-force controller. A rotor angular velocity is utilized to estimate the acceleration. The validity of the proposed controller is verified through frequency analysis, simulation, and experiment.