Yoshihisa Hirane

Levitation drift of flywheel and HTSC bearing system caused by mechanical resonance

Abstract The stability of positioning is one of the most important characteristics in flywheel energy storage systems with high-temperature superconducting (HTSC) magnetic bearing. In this paper, we experimentally discuss the drift of the levitation gap in the flywheel system under the revolution. When the revolution speed of the flywheel rotor passes through the mechanical resonant frequencies, the dynamics of the rotor show the self oscillatory vibration. The vibration has a possibility to induce the nonlinear response which depends on the hysteretic force-displacement relation of HTSC bearing system. The experimental results show substantial levitation drift caused by the gyroscopic and the translational motion.

Speed regulation of an induction motor using model reference adaptive control

A novel approach of constructing a robust variable-speed drive system using an induction motor supplied from a voltage-source-type PWM inverter is discussed. The inverter is controlled so as to generate the fabricated terminal voltages based on the voltage-decoupled transvector control theory where neither a current feedback loop nor a current limiter circuit is required. Although the hardware for this decoupling method becomes simplified, it still has some disadvantages, such as the discrepancy between the command currents and actual currents. Incorporated into the drive system described herein is the optimal-speed regulator adopting the exact model-matching method, which fulfills the function of a compensator for unfavorable errors. The operating characteristics of the proposed drive system are compared with conventional PI control to verify the effectiveness under various conditions by investigating the transient responses for the step change of the speed command, the load torque, and so forth.

Suppression of harmonic voltage distortion by neural network controlled active filter

A newly developed control algorithm using a neural network theory for an active AC harmonic filter system to reduce the harmonic voltage distortion in an electrical power system is presented. The new control philosophy is dedicated to the reduction of the harmonic voltage distortion caused by many distributed harmonic generating loads. Harmonic disturbance problems, the neural network control algorithm of the active filter, and test results on a small-scale power system simulator are presented. The voltage distortion becomes lower than 1% because of the active filter operation, even under the condition that maximum voltage distortion exceed 7% without the active filter. The response time of the harmonic voltage compensation control is shown to be within two seconds.<<ETX>>

A System for Computer-Assisted Design of Stent-Grafts for Aortic Aneurysms Using 3-D Morphological Models

A three-dimensional model was constructed from helical CT images for abdominal aortic aneurysm (AAA) and thoracic aortic aneurysm (TAA). A stent-graft was designed and positioned endoluminally on the computer. One hundred and nine stent-grafts for 101 patients were designed by this method and deployed well in all patients. The design time was reduced from 4 to 0.5 hr.

The Basic Characteristics of the Pinning Force and Flux Density Distribution of the HTSC-Permanent Magnet Hybrid Bearing

A basic experimental device for a bearing system using high temperature superconducting material (HTSC) is introduced. In this system, a circular shaped permanent magnet is installed on the rotor, and a YBaCuO plate is used for the stator. To increase the levitation force, an additional circular permanent magnet is installed under the YBaCuO plate in the stator. Influence of the additional permanent magnet on the flux density distribution is shown. From the result, the shape of the ring superconductor is designed to increasing the lateral stability.

Harmonic voltage suppression by active filter with neural network controller

The increase of power devices adopted in built-in power supplies is accompanied with an increase of many distributed harmonic generating loads and the harmonic problem in 6.6 kV power distribution lines is becoming prominent. To cope with harmonics, either conventional LC filters or active filters are used as additional compensators near the harmonic generating load. However such devices are not optimal when adopted as compensators in the power distribution system. The authors describe a neural network controlled active filter to realize both stable and adequate compensation for parameter variation due to impedance change or load variation and then discuss a computer simulation followed by the results obtained using a small scale laboratory model.<<ETX>>

Control and characteristics of magnetically levitated system with linear induction motor

Using the magnetically levitated system with linear induction motor (LIM), stable levitated motions were obtained at complete slip state without any contact to the guide way. The obtained results are as the system configuration of the proposed magnetically levitated system with linear induction motor is very simple. By using the switching function of the gap displacement and the velocity of the displacement, the levitated motion can be stabilized to the periodic motion. The stable levitated motion has a little periodical oscillation which frequency coincides with 120 Hz. On the basis of these experimental results, the authors are going to develop a new prototype vehicle to control the driving force of LIM.<<ETX>>

A measurement of a magnetic field vector-application of the magneto-birefringence effect by magnetic fluid

The measurement of a magnetic field vector using the magneto-birefringence effect in a magnetic fluid is discussed, and the characteristics of the experimental system are described. The system applies a laser diode and a thin film of magnetic fluid as a refracting element to measure magneto-birefringence. Magnetic fluids have both a large anomalous magneto-birefringence effect and a Faraday effect. These effects cause the change of intensity and the phase shift of a refracted laser beam. In the experimental system, a method for detecting these effects is proposed. On the basis of the experimental results, it is clear that the direction and the intensity of a two-dimensional magnetic field vector can be measured in the cases of both direct and alternating magnetic fields. >

Theoretical Assessment of a Variable-Frequency Envelope Cycloconverter

The operating principles and characteristics of a proposed variable-frequency envelope cycloconverter, constructed with relatively few thyristors, for three-phase variable-speed induction motor drive, are described. As the output frequency is varied, the output voltage wave-forms created by triggering the thyristors are found to vary for both the amplitude of the harmonic components and their phase displacements. Distortion factors, unbalance factors of the three-phase output voltages, and the nominal conversion efficiency of the system are given.

Experimental study of a PM‐HTSC hybrid magnetic levitation system

A principle of hybrid magnetic levitation system using permanent magnets (PMs) and high-temperature superconductors (HTSCs) for a linear-motor-type carrier system in a high-quality clean room and a magnetic bearing for the flywheel energy storage system are discussed. A substantial levitation force was generated by the repulsive force between like poles of coupled magnets. However, the repulsion system with magnets is essentially unstable without control. Thus, HTSCs are applied for control elements of the PM-HTSC hybrid magnetic levitation system. In this system, the levitation force becomes stronger than in the system without PM, and we can expect sandwich-type magnetic bearing capable of sustaining greater force.