Hiroyuki Ohsaki

Electromagnetic Design of 10 MW Class Fully Superconducting Wind Turbine Generators

We have studied a 10 MW class fully superconducting synchronous machine for direct-drive wind turbine generators. This machine has been designed using two kinds of superconducting wires. Multifilament wires have been used for armature windings. The DC field coils of the machine rotor are made of HTS tapes. Electromagnetic design of the generators has been carried out by FEM analysis. Analysis results show that 10 MW output is achievable with less use of HTS tapes than wind turbine generators having superconducting field coils and copper armature windings. Then, calculated AC losses are low.

Comparison of Conventional and Superconducting Generator Concepts for Offshore Wind Turbines

This paper deals with the comparison of electromagnetic characteristics of 10 MW class direct-drive wind turbine generators for offshore wind farms. Four kinds of wind turbine generators including a conventional permanent magnet generator, a salient/nonsalient pole superconducting generator, and a fully superconducting generator are investigated. Electromagnetic characteristics for these generators have been investigated with FEM analysis. The results show that a fully and a salient pole type superconducting wind turbine generators have a potential for 10 MW class offshore wind turbine generators from the aspect of size and economical points.

Electromagnetic Design Study of Transverse Flux Enhanced Type Superconducting Wind Turbine Generators

Transverse flux enhanced type superconducting synchronous machines have been studied for large-capacity wind power generation. The generators have multiple circular superconducting field coils in the rotor and copper armature windings in the stator. A parametric design study and electromagnetic characteristic analysis of the superconducting wind turbine generators (WTGs) have been carried out. The target output is 10 MW for a rotational speed of 10 rpm, and the diameter of the whole coil system is 5 m. Superconducting technology is quite effective for compact and lightweight design of large power capacity, low-speed and high torque generators. Armature and field coil dimensions and the number of poles are key parameters in the design study. FEM analysis was carried out to obtain magnetic flux density, magnetic flux linkage, induced voltage, fundamental generator characteristics, etc. Required superconducting wire length was also estimated.

Electromagnetic design study of 10 MW-class wind turbine generators using circular superconducting field coils

A new rotor design has been proposed for wind turbine generators using circular superconducting (SC) field coils. The target power output is 10 MW for 10 rpm. A fundamental 3D FEM parametric study has been carried out to reveal the electromagnetic characteristics of the machines. As machine diameter & pole number are the key parameters for electric machines, they were studied precisely. Electromagnetic force and hoop stress were also calculated for rotor coil models. A simple stator winding design has been proposed and generator characteristics were analyzed. Minimization of superconducting wire length and machine size were the highest priority for the electromagnetic design analysis. Though we focused on air-core models in this research, back-iron models were also designed to understand the effect and advantages of the back-iron.

Superconducting Power Cable Application in DC Electric Railway Systems

A superconducting power cable is a prospective application of high-temperature superconductors. Although power cables using Bi2223 or YBCO wires have been developed in the world so far mainly for utility grid application, we focus attention on railway application of a superconducting power cable. We have studied how to introduce superconducting power cables effectively and economically to a dc electric railway. Numerical analysis models based on the MATLAB-Simulink are constructed for a dc electric feeder system of singe- and double-track railways. Tractive force and train resistance characteristics are modeled. Energy saving by the superconducting power cable is investigated with the influences of the number of substations, the train operation interval, etc., taken into account. The results show that the superconducting power cables can improve regeneration rate and system energy saving, and reduce the substation capacity very effectively. It will be also an advantage that if the transportation capacity of a railway line needs to be increased, the introduction of superconducting cables could achieve it without changing the existing substations along the line.

AC Losses of a Grid-Connected Superconducting Wind Turbine Generator

We present a numerical method to estimate the steady-state AC losses of a superconducting wind turbine generator connected to the grid through its AC/DC/AC converter. We use a multiscale simulation with unidirectional couplings between a lumped-parameter wind energy conversion system model, a finite element machine model, and a finite element HTS tape model. The estimation include effects linked to the generator space harmonics, the exciter control, and the AC/DC/AC converter PWM and control. As the superconducting coil is made of several thousand of HTS tapes, we evaluate AC losses for a fraction of them and we interpolate the results to the others. The steady-state AC losses of a 10 MW class generator are estimated to be under 60 W.

Eccentric Figure-Eight Coils for Transcranial Magnetic Stimulation

Previously we proposed an eccentric figure-eight coil that can cause threshold stimulation in the brain at lower driving currents. In this study, we performed numerical simulations and magnetic stimulations to healthy subjects for evaluating the advantages of the eccentric coil. The simulations were performed using a simplified spherical brain model and a realistic human brain model. We found that the eccentric coil required a driving current intensity of approximately 18% less than that required by the concentric coil to cause comparable eddy current densities within the brain. The eddy current localization of the eccentric coil was slightly higher than that of the concentric coil. A prototype eccentric coil was designed and fabricated. Instead of winding a wire around a bobbin, we cut eccentric-spiral slits on the insulator cases, and a wire was woven through the slits. The coils were used to deliver magnetic stimulation to healthy subjects; among our results, we found that the current slew rate corresponding to motor threshold values for the concentric and eccentric coils were 86 and 78 A/µs, respectively. The results indicate that the eccentric coil consistently requires a lower driving current to reach the motor threshold than the concentric coil. Future development of compact magnetic stimulators will enable the treatment of some intractable neurological diseases at home.

Design and characteristic analysis of 10 MW class superconducting wind turbine generators with different types of stator and rotor configurations

Wind power generation facilities have been installed in the world. Recently offshore wind energy attracts greater attention, and development of wind turbine generators of higher power rating becomes more important. Superconducting technologies is expected to be applied to over 10 MW class generators. We have studied 10 MW class large wind turbine generators using superconducting technologies. The paper presents fundamental structures of large-scale wind turbine generators, paying attention to the reduction of superconducting wire length, and generator size and weight. Some design results of 10 MW wind turbine generators are shown and compared.

Back-to-back converter design and control for synchronous generator-based wind turbines

We present a step-by-step method for the design and control of a full-scale back-to-back converter for wind energy conversion systems using direct-drive electrically excited synchronous generators. First the system modeling is described in details. Then the converter controllers are designed and their PI parameters are systematically calculated using the symmetrical optimum method. Finally, the performances of a 2 MW class generator connected to the grid through the obtained converter are evaluated through simulations.

Electromagnetic characteristics of eccentric figure-eight coils for transcranial magnetic stimulation: A numerical study

Repetitive transcranial magnetic stimulation (rTMS) is effective for treatment of several neurological and psychiatric diseases. We proposed an eccentric figure-eight coil, which induces strong eddy currents in the target brain tissue. In this study, numerical analyses were carried out to obtain magnetic field distribution of the eccentric figure-eight coil and eddy current in the brain. The analyses were performed with various coil design parameters, such as the outer and inner diameters and number of turns, to investigate the influence of these parameters on the coil characteristics. Increases in the inner diameter, outer diameter, and number of turns caused increases in the maximum eddy current densities. Coil inductance, working voltage, and heat generation also became higher with the increases in these design parameters. In order to develop a compact stimulator system for use at home, we need to obtain strong eddy current density, keeping the working voltage as low as possible. Our results show that it is effective to enlarge the outer diameter.Repetitive transcranial magnetic stimulation (rTMS) is effective for treatment of several neurological and psychiatric diseases. We proposed an eccentric figure-eight coil, which induces strong eddy currents in the target brain tissue. In this study, numerical analyses were carried out to obtain magnetic field distribution of the eccentric figure-eight coil and eddy current in the brain. The analyses were performed with various coil design parameters, such as the outer and inner diameters and number of turns, to investigate the influence of these parameters on the coil characteristics. Increases in the inner diameter, outer diameter, and number of turns caused increases in the maximum eddy current densities. Coil inductance, working voltage, and heat generation also became higher with the increases in these design parameters. In order to develop a compact stimulator system for use at home, we need to obtain strong eddy current density, keeping the working voltage as low as possible. Our results show that ...