Yoshishige Murakami

Bio: Yoshishige Murakami is an academic researcher from Osaka University. The author has contributed to research in topics: Superconducting magnet & Superconducting magnetic energy storage. The author has an hindex of 9, co-authored 74 publications receiving 739 citations.

Application of superconducting magnet energy storage to improve power system dynamic performance

Abstract: The application of superconducting magnet energy storage (SMES) to the stabilization of a power system with long-distance bulk power transmission lines which has the problem of poorly damped power oscillations is presented. Control schemes for stabilization using SMES capable of controlling active and reactive power simultaneously in four quadrant ranges are proposed. The effective locations and the necessary capacities of SMES for power-system-stabilizing control are discussed in detail. Results of numerical analysis and experiments in an artificial power-transmission system demonstrate the significant effect of the control by SMES on the improvement of power-system oscillatory performance. >

Terahertz radiation from superconducting YBa2Cu3O7−δ thin films excited by femtosecond optical pulses

Abstract: Ultrashort electromagnetic waves (600 fs width) from superconducting YBCO thin films have been observed by irradiating current‐biased samples with femtosecond optical laser pulses (80 fs width). The Fourier component of the pulse extends up to ∼2 THz. The characteristics of the radiation are studied and the radiation mechanism is ascribed to the ultrafast supercurrent modulation by the laser pulses, which induce the nonequilibrium superconductivity.

Ultrashort Electromagnetic Pulse Radiation from YBCO Thin Films Excited by Femtosecond Optical Pulse

Abstract: We have observed ultrashort electromagnetic pulse radiation from YBa2Cu3O7-δ thin-film dipole antennas. The supercurrent transient is created by the excitation of the supercarriers into quasiparticles with a femtosecond laser pulse, and freely propagated electromagnetic pulses are measured and characterized. A pulse with 0.5 ps full width at half-maximum was obtained, containing frequency components up to 2.0 THz. A femtosecond time-resolved characterization of the spectra revealed that they strongly depend on the excitation conditions, and the quasiparticle recombination time becomes longer with increase in the excitation intensity. It is also observed that the radiation power increases in proportion to the square of both the bias current and the laser power in the region of weak excitation, which is consistent with the classical theory based on a two-fluid model. In the region of strong excitation, deviation from the classical theory was observed.

Simultaneous Active and Reactive Power Control of Superconducting Magnet Energy Storage Using GTO Converter

Abstract: By using GTO's (Gate Turn-Off Thyristor) in place of ordinary thyristors in a conventional six pulse Greatz bridge converter, forced commutation is possible, so in the usage of ac-dc power conversion the reactive power of not only lagging but also leading phase can be absorbed. This feature enables superconducting magnet energy storage (SMES) to control reactive power in the wide range between lagging and leading phases. By virtue of this control ability , SMES will be applicable for a power system stabilyzer. A GTO converter which mainly consists of six GTO's was developed and tested. In this GTO converter, the energy stored in leakage inductances of the transformer is handled by voltage clipper circuit. Then, by using two sets of these GTO converters, we carried out some experiments of simultaneous active and reactive power control of SMES. The experiments on the developed control system were successfully performed and the ability of controlling reactive power in the wide range between lagging phase and leading phase was verified.

Enhanced THz radiation from YBCO thin film bow-tie antennas with hyper-hemispherical MgO lens

Abstract: We demonstrate power enhancement of terahertz (THz) radiation from YBCO thin films. An ultra-wide-band electromagnetic pulse, which contains frequency components over 3 THz, was excited by ultrafast supercurrent modulation with femtosecond optical pulse irradiation. The maximum THz radiation power emitted into free space was achieved up to 0.5 /spl mu/W with the combination of a bow-tie antenna and an MgO hyper-hemispherical lens. We discuss the radiation power dependence on temperature, excitation power, and bias supercurrent.

Energy storage systems for advanced power applications

Abstract: While energy storage technologies do not represent energy sources, they provide valuable added benefits to improve stability power quality, and reliability of supply. Battery technologies have improved significantly in order to meet the challenges of practical electric vehicles and utility applications. Flywheel technologies are now used in advanced nonpolluting uninterruptible power supplies. Advanced capacitors are being considered as energy storage for power quality applications. Superconducting energy storage systems are still in their prototype stages but receiving attention for utility applications. The latest technology developments, some performance analysis, and cost considerations are addressed. This paper concentrates on the performance benefits of adding energy storage to power electronic compensators for utility applications.

An Overview of SMES Applications in Power and Energy Systems

Abstract: Superconducting magnetic energy storage (SMES) is known to be a very good energy storage device. This article provides an overview and potential applications of the SMES technology in electrical power and energy systems. SMES is categorized into three main groups depending on its power conditioning system, namely, the thyristor-based SMES, voltage-source- converter-based SMES, and current-source-converter-based SMES. An extensive bibliography is presented on the applications of these three types of SMES. Also, a comparison is made among these three types of SMES. This study provides a basic guideline to investigate further technological development and new applications of SMES, and thus benefits the readers, researchers, engineers, and academicians who deal with the research works in the area of SMES.

Output levelling of renewable energy by electric double-layer capacitor applied for energy storage system

Abstract: Utilization of renewable energy are coming up from view points of environmental conservation and depletion of fossil fuel. However, the generated power from renewable energies is always fluctuating due to environmental status. Energy storage system is indispensable to compensate these fluctuating components. Energy capacitor system (ECaSS) connected an electric double-layer capacitor (EDLC) with power-electronics devices is useful for the compensation of fluctuating power since one is capable of controlling both active and reactive power simultaneously. This paper proposes the current-source ECaSS (CS-ECS), which consists of EDLC, bi-directional DC-DC converter, and current-source inverter. We have presented the control system for the active/reactive power control of CS-ECS, and have shown the effectiveness of CS-ECS through computer simulations for case of wind power generation system.

High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics

Abstract: The THz-radiation power from bulk InAs irradiated with femtosecond optical pulses is significantly enhanced and reaches 650 μW in a 1.7-T magnetic field with 1.5-W excitation power. The THz-radiation power is related almost quadratically both to the magnetic field and excitation laser power. We have also found that the power of the THz-radiation from an InAs sample in a magnetic field is over one order of magnitude higher than that from GaAs. Additionally, a dramatic change of ellipticity is observed, and the spectra of the horizontal and vertical polarization components are found to differ.