Superconducting Bearing System Research Articles

A fully superconducting bearing system for flywheel applications

A fully superconducting magnetic suspension structure has been designed and constructed for the purpose of superconducting bearing applications in flywheel energy storage systems. A thrust type bearing and two journal type bearings, those that are composed of melt textured high-Tc superconductor YBCO bulks and Nd-Fe-B permanent magnets, are used in the bearing system. The rotor dynamical behaviors, including critical speeds and rotational loss, are studied. Driven by a variable-frequency three-phase induction motor, the rotor shaft attached with a 25 kg flywheel disc can be speeded up to 15 000 rpm without serious resonance occurring. Although the flywheel system runs stably in the supercritical speeds region, very obvious rotational loss is unavoidable. The loss mechanism has been discussed in terms of eddy current loss and hysteresis loss.

Study of damping in 5 kWh superconductor flywheel energy storage system using a piezoelectric actuator

A 5kWh superconductor flywheel energy storage system (SFES) has advantages in terms of high electrical energy density, environmental affinity and long life. However, the SFES has disadvantage that electromagnetic damper is needed because superconducting bearings do not have enough damping coefficient. The purpose of this experiment is to develop a method of damping the vibration of the SFES.A piezoelectric actuator was attached to a superconducting bearing system for feasibility test in order to make it as a damper of the SFES. For this experiment, a cylindrical permanent magnet (PM) 40mm in diameter and 10mm height was used as a rotor, a high-temperature superconductor bulk (HTS bulk) with dimensions 40mm×40mm×15mm was used as a stator, and two vibration exciters (an upper and a lower vibration exciter) and a piezoelectric actuator were used. The PM was fixed on the upper vibration exciter. The HTS bulk was fixed on either the lower vibration exciter to test for damping in the feasibility test, or on the piezoelectric actuator for the actual SFES. The conditions of this experiment included various voltage outputs of a power amplifier to the lower vibration exciter, moving distances of the piezoelectric actuator which are displacements of the HTS bulk, and phase differences between the upper and lower vibration exciter or the piezoelectric actuator.The damping feasibility test was conducted with a 300μm gap between the PM and HTS bulk with a PM vibration of 30μm. For the actual SFES test, the gap between the PM and HTS bulk was 1.6mm and the PM vibration was 25μm. The following conditions were conducted to optimize: an appropriate voltage input to the lower vibration exciter or a displacement of piezoelectric actuator and an appropriate phase difference. When the piezoelectric actuator was used, the damping effect was greatly improved up to 92.32% which a displacement of damped PM was 1.92μm.

Subharmonic Resonance of a Rotor Supported by a High-Tc Superconductor

This paper investigates subharmonic resonance, one of typical nonlinear phenomena, appearing in a high-Tc superconducting bearing system. In such low-damping systems having noncontact support by magnetic force, complex dynamical behaviors can be caused by nonlinearity of the magnetic force. In this study, the magnetic rotor, supported by a high-Tc superconducting bulk, is bound to a D.C. motor with a universal joint. According to the equation of motion, caused by the quadratic term of the levitation force, subharmonic resonance of the rotor can occur when the rotor rotates, not at its critical speed, but at twice its critical speed. This analytical prediction was confirmed by our numerical and experimental results. Additionally, our study also found occurrence of internal resonance induced by this subharmonic resonance. These findings beyond linear regimes can be important for the design of high-Tc superconducting levitation systems.

Effects of Spin-Up Rate on Internal Resonance in a High- $Tc$ Superconducting Bearing System

This paper investigates the transient behaviors of a rotor passing through resonance in a high- Tc superconducting bearing system. Such a low-damping multidegree-of-freedom system, which is subjected to nonlinear force, can show complex dynamical behaviors, in which energy transfer occurs between modes through nonlinear coupling. Our numerical and experimental results show that, in a system of a high-Tc superconducting bearing, internal resonance can occur even in transient cases where the rotor passes through resonance. The effects of the internal resonance and also the effects of the spin-up rate on the transient dynamics of the rotor have been examined and clarified by changing the period of increasing voltage applied to a direct-current motor for rotating the rotor.

Effects of Spin-Up Rate on Internal Resonance in a High-Tc Superconducting Bearing System

Effects of Spin-Up Rate on Internal Resonance in a High-Tc Superconducting Bearing System

Parametric dynamic analysis of a superconducting bearing system

The dynamics of a disk-shaped permanent-magnet rotor levitated over a high-temperature superconductor is studied. The interaction between the rotor magnet and the superconductor is modelled by assuming the magnet to be a magnetic dipole and the superconductor as a diamagnetic material. In the magneto-mechanical analysis of the superconductor part, the frozen image concept is combined with the diamagnetic image and the damping in the system was neglected. The interaction potential of the system is the combination of magnetic and gravitational potential. From the dynamical analysis, the equations of motion of the permanent magnet are stated as a function of lateral, vertical and tilt directions. The vibration behaviour of the permanent magnet is analyzed with a numerical calculation obtained by the non-dimensionalized differential equations for small initial impulses.

Effect of the ratio between the natural frequencies of a high- Tc superconducting bearing system on internal resonance

High- T c superconducting levitation systems can achieve stable levitation without control, but they also often show complex nonlinear dynamical behavior such as internal resonance, in which different modes resonate at the same time. This paper investigates numerically and experimentally effect of the ratio between the natural frequencies of different modes on their internal resonance in a high- T c superconducting magnetic bearing system. Numerical analyses based on the flux frozen method have been conducted. Responses in the case that the ratio of the natural frequencies is 2 to 1 are compared with those in the case that the ratios have some difference from 2 to 1. Numerical results show that the internal resonance occurs even in the cases that the ratio has some difference, though limited, from 2 to 1, and that the more the ratio differs from 2 to 1, the more the frequency range of the resonance is shifted and the narrower it is. Experiments have also been carried out. Experimental results of the internal resonance are similar to the numerical ones qualitatively.

酸化物高温超電導体を用いた超電導軸受構造の動特性

We have studied a superconducting bearing system using high-Tc superconductors with a strong pinning force. The superconducting bearing system consists of a superconductor prepared by quench and melt growth (QMG) method and a set of alternating-polarity magnets. This paper describes the dynamic characteristics of the superconducting bearing system with small damped vibrations. An impulse force was applied to the set of alternating-polarity magnets levitated over the superconductor of the system. The vibrations of the set of magnets were measured using a laser displacement meter. Stiffness, damping coefficient, and energy loss of the superconducting bearing system were discussed. The results show that the dynamic characteristics of the bearing system are closely related to the static characteristics. It is necessary to evaluate the dynamic characteristics of the superconducting bearing system in applying the system to a radial bearing with a high rotation speed.