Daisuke Miyagi

Application of SMES and Fuel Cell System Combined With Liquid Hydrogen Vehicle Station to Renewable Energy Control

It is an urgent issue to reduce global carbon-dioxide in the world, and hence the renewable energy, that is environmentally friendly, should be supplied as a large amount of the electric power. Since installation of a large amount of the fluctuating renewable energy, such as wind turbine and photovoltaic, will cause the power utility network unstable, we propose an advanced superconducting power conditioning system (ASPCS) that is composed of Electrolyzer-Hydrogen-FC and SMES cooled with liquid hydrogen from a station for vehicles. The ASPCS has a function of compensating the fluctuating renewable energy with SMES that has quick response and large I/O power, and with that has moderate response and large capacity. The SMES is wound with superconductor with a critical temperature of 39 K from an economical point of view, because it is cooled with through a thermo-siphon system to keep safety against a flammable gas. The ASPCS effectively fulfills a power balance by applying a statistical prediction method of Kalman filter algorithm. The capacity of SMES is optimized by using the trend prediction for a number of wind power data. The overall electric efficiency of the ASPCS is evaluated for a typical wind generator.

Design Study of SMES System Cooled by Thermo-Siphon With Liquid Hydrogen for Effective use of Renewable Energy

In order to use effectively renewable energy sources, we propose a new system, called Advanced Superconducting Power Conditioning System (ASPCS), that is composed of SMES and Fuel Cell-Electrolyzer (FC-EL) in connection with a liquid hydrogen station for vehicles. The new system will compensate the fluctuating renewable energy sources with SMES having characteristics of quick response and large I/O power, and with FC-EL having characteristics of moderate response and large storage capacity. The SMES coil with an MgB2 conductor operated at 20 K is cooled with a thermo-siphon cooling system by using cryogen from the liquid hydrogen station. The necessary minimum storage capacity of SMES is estimated as 50 MJ for compensating output power of 1 MW. A four-pole SMES coil is designed by using stranded cable concept. The design study of the SMES coil composed of the MgB2 conductor and the thermo-siphon cooling system is reported.

Effect of Carrier Frequency and Circuit Resistance on Iron Loss of Electrical Steel Sheet Under Single-Phase Full-Bridge PWM Inverter Excitation

The pulse width modulation (PWM) inverter has been used for the control of a motor since the rotating speed can be changed efficiently and easily. In order to estimate the iron loss in an iron core with sufficient accuracy under a PWM inverter excitation, it is necessary to understand correctly the influence of operating condition and circuit parameter on iron losses. In this paper, we measured magnetic properties of the nonoriented electrical steel sheet excited by a single-phase full-bridge PWM inverter using a ring specimen that corresponds to a magnetic circuit of an actual motor core. The effect of the carrier frequency and circuit resistance on the iron loss and the behavior of minor loops was examined. It is shown that the iron loss is increased when the circuit resistance is increased due to the generation of minor loops. Therefore, the circuit resistance should be decreased in an actual motor system.

Design Study of

In order to use effectively renewable energy sources such as wind and photovoltaic power generations, we propose a new system, called Advanced Superconducting Power Conditioning System (ASPCS), that is composed of superconducting magnetic energy storage (SMES), fuel cell-electrolyzer (FC-EL), hydrogen storage, dc/dc and dc/ac converters, and controller. The new system compensates the fluctuating electric power generations with SMES having characteristics of quick response and large I/O power and with hydrogen energy having characteristics of large storage capacity. The ASPCS will be combined with a liquid hydrogen station for FC vehicles. The SMES is a key component of the ASPCS to compensate the fast fluctuations of the renewable energy generations that cannot be compensated by prediction using the Kalman filtering method. The design study of the 50 MJ SMES coil was performed with an MgB2 conductor to be operated at 5 T maximum and 20 K by using liquid hydrogen of the FCV stations. The stability and ac losses of the coil were estimated in this study.

\hbox{MgB}_{2}

The superconducting magnet is effective to get a high stable and high magnetic field for magnetic resonance imaging (MRI). The current MRI superconducting magnet needed cooling in the liquid helium (4.2 K) to use NbTi superconducting wire. In the past few years, price increase and low availability of liquid helium has become a serious problem. Under such circumstances, the development of a high-temperature superconducting (HTS) coil dispensing with liquid helium cooling is greatly desired. The research and development project of the high stable magnetic field ReBCO coil system fundamental technology that started from the latter half of 2013 develops a ReBCO coil for 3 T MRI superconducting magnets. It gets a prospect of the practical use as the final aim. In this project, we will produce an HTS test coil of 300 mm bore experimentally and evaluate the magnetic field. This coil is cooled in less than 20 K by a GM refrigerator. We are going to make MRI used by the ReBCO coil field to evaluate the uniformity and stability of the magnetic field.

SMES Coil for Effective Use of Renewable Energy

In the electromagnetic field computation in consideration of nonlinear magnetic anisotropy, the solution by the Newton-Raphson method has some problems which are an asymmetric matrix and poor convergence characteristic. We applied the Fixed-Point method to the electromagnetic field computation in consideration of nonlinear magnetic anisotropy and examined the usefulness of the Fixed-Point method through comparing the Fixed-Point method with the ordinary Newton-Raphson method. The Fixed-Point method with a symmetric matrix is quite faster than the Newton-Raphson method with an asymmetric matrix. Therefore, the Fixed-Point method is a very useful technique in nonlinear magnetic anisotropy problems.

Research and Development of the High Stable Magnetic Field ReBCO Coil System Fundamental Technology for MRI

We investigated the characteristics of transport current loss against distorted current with odd-order harmonic component using a Bi2223 short sample conductor. We measured the transport current loss against the distorted current with the 3rd, 5th, or 7th harmonic as a function of the amplitude of each harmonic current. The transport current loss per cycle of fundamental frequency against the distorted current was independent of the fundamental frequency and was compared with the sum of transport current losses against the sinusoidal current with the amplitude of each harmonic current component obtained by Fourier analysis. Fair agreement was obtained in the distorted current with the 3rd harmonic, while a big difference was observed in the distorted current with the 5th or 7th harmonic. Independent of harmonic order, the transport current loss against the distorted current was almost the same as the sum of the transport current losses against the sinusoidal current with the amplitude of the distorted current corresponding to a major hysteresis loop and the amplitude of the small rise and fall of the distorted current corresponding to a minor hysteresis loop that can be directly estimated from the distorted current waveform.

Usefulness of Fixed Point Method in Electromagnetic Field Analysis in Consideration of Nonlinear Magnetic Anisotropy

Purpose – The purpose of this paper is to examine the mechanism of the increase or decrease of eddy current loss of the segmented Nd‐Fe‐B sintered magnets without insulation, and the effects of parameters on such a phenomenon are discussed.Design/methodology/approach – The measured contact resistance is used in the finite element analysis.Findings – It is shown that the eddy current loss in a magnet shows the peak value when the number of segments are increased at 40 kHz, but this property is changed at low frequency (10 kHz). Its tendency is changed by the contact resistance and the permeance (surrounding iron core).Originality/value – The reason of a curious property of eddy current loss of segmented magnets is clearly explained by examining the eddy current distribution at various contact resistances.

Transport Current Loss Characteristics of HTS Tape With Odd-Order Harmonic Current

Wireless power transmission has been investigated to realize more efficient and more convenient noncontact power transmission systems for electric tramways, electric vehicles, portable telephones, and so on. Since the magnetic resonance type wireless power transmission system is often used in frequency regions of megahertz, there are some problems, such as the increase of wire resistance due to skin effect and a switching loss in converter. Therefore, it is expected to realize high-power wireless power transmission in low-frequency regions of kilohertz. In a wireless power transmission system using copper coils, however, the transmission efficiency decreases with the decrease of resonance frequency because quality factor decreases with the decrease of the resonance frequency. Therefore, we fabricated a model system using high-temperature superconducting (HTS) double-pancake coils composed of REBCO tape and investigated the transmission efficiency characteristics to evaluate the possibility of application of the HTS coil to a high-efficiency wireless power transmission system operated in the low-frequency region of kilohertz. In the copper coil system, the transmission efficiency increases with the resonance frequency. In the HTS coil system, however, a high-efficiency transmission was obtained, even at a low-resonance frequency, due to a large quality factor at low frequency. Moreover, in the wireless power transmission system using HTS coils, the transmission efficiency was high not only at the resonance frequency but also around the resonance frequency. From these results, we believe that HTS coil can realize the high-efficiency wireless power transmission in a low-frequency region of kilohertz.

Eddy current losses of segmented Nd‐Fe‐B sintered magnets without insulation under various conditions

Generally, high magnetic flux density is adopted in superconducting magnetic energy storage (SMES) coil design to reduce superconducting coil size and increase energy density. However, critical current density of the SMES coil is degraded by applying the high magnetic flux density to superconducting wire. This means that adopting the high magnetic flux density is not necessarily suitable for the superconducting wire reduction of the SMES coil. In this paper, the relationship between the maximum magnetic flux density within coil and superconducting wire usage of the SMES coil composed of solenoid or toroidal coil wound by MgB2, Bi2223, or REBCO wire was investigated. As a result, most suitable magnetic flux density within SMES coil for realizing the minimum superconducting wire usage in MgB2 , Bi2223, and REBCO wires were clarified. How to estimate the most suitable maximum magnetic flux density within coil for realizing the minimum wire usage in each superconducting wire was also investigated. Comparison between the rate of change of coil radius times maximum magnetic flux density and critical current density with respect to the maximum magnetic flux density is useful for obtaining the suitable maximum magnetic flux density for the minimum superconducting wire usage.