• 한국정밀공학회지
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• 제25권3호
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• pp.83-92
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• 2008

This paper develops the theory for a fault-tolerant, permanent magnet biased, homopolar magnetic bearing. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a novel distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate the theory. Simulations show that very much the same dynamic responses (orbits or displacements) are maintained throughout failure events (up to any combination of 3 coils failed for the 6 pole magnetic bearing) while currents and fluxes change significantly. The overall load capacity of the bearing actuator is reduced as coils fail. The same magnetic forces are then preserved up to the load capacity of the failed.

• Journal of Magnetics
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• 제18권4호
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• pp.443-453
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• 2013

Maglev wind turbine generator (MWTG) technology has been widely studied due to its low loss, low maintenance cost, and high reliability. However, the dynamics of the magnetic bearing system differ fromthe those of the traditional mechanical bearing system. A horizontal axial MWTG supported with a permanent magnetic bearing is designed in this research and the radial forces and the natural frequencies of the rotor system are studied. The results show that the generatorhas a cyclical magnetic forceand an unreasonable bearing stiffness may mean that the rotor system needs to work in the resonance region; the bearing stiffness is the key factor to avoid this problem. This is the main rule of the bearing stiffness design in the MWTG, and this rule can also be used in other maglev permanent magnet motors.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1995년도 춘계학술대회
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• pp.179-182
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• 1995

Although air, water, and noise pollutions have been widely recognized, electromagnetic forces(EMF) hazard has been rarely recognized as a pollution and very little studies has been done in this country. Thus, in this study electromagnetic forces radiated by various home appliances, once machines, and communication equipments were measured and so were several places radiating strong EMF such as subway stations and electric substations. Among the home appliances microwave oven senates lots of magnetic field and microwaves, and electric mattress does strong magnetic field. In video game room strong magnetic and considerable electric fields were measured. It was observed strong magnetic field inside of electric powered train and very strong magnetic and electric fields on some platforms. Hand-phone and car-phone radiate very hazardous level of microwaves to brain and that they rapidly come into wide use. In this study data base for various electric machines and places radiating strong EMFs were constructed and could be used for future epidemiological studies.

• 대한전기학회논문지:전력기술부문A
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• 제48권3호
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• pp.278-285
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• 1999

This paper utilizes the method of Q-parameterization control to design a controller which solves the problem of imbalance in magnetic bearing systems. There are two methods to solve this problem using feedback controal. The first method is to compensate for the imbalance forces by generating opposing forces on the bearing surface (imbalance compensation). The second method is to make the rotor rotate around its axis of inertia (automatic balancing);in this case no imbalance forces will be generated. In this paper we deal with only imbalance compensation. The free parameter of the Q-parameterization controller is chosen such that these goals are achieved. After the introduction of a model of the magnetic bearing system, we explain the Q-parameterization controller design of the magnetic bearing system with emphasis on the rejection of sinusoidal disturbance for imbalance compensation design. The design objectives are formulated as a linear equations in the controller free paramete Q. Finally, simulation and experimental results are presented and showed the robustness and effectiveness of the proposed controllers.

• Progress in Superconductivity
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• 제14권1호
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• pp.39-44
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• 2012

The fabrications condition and superconducting properties of top-seeded melt growth (TSMG) processed $GdBa_2Cu_3O_{7-y}$ (Gd123) bulk superconductors were studied. Processing parameters (a maximum temperature ($T_{max}$), a temperature for crystal growth ($T_G$) and a cooling rate ($R_G$) through a peritectic temperature ($T_P$) for the fabrication of single grain Gd123 superconductors were optimized. The magnetic levitation forces, trapped magnetic fields, superconducting transition temperature ($T_c$) and critical current density ($J_c$) of the Gd123 bulks superconductors were estimated. Single grain Gd123 bulk superconductors were successfully fabricated at the optimized processing condition. The $T_c$ of a TSMG processed Gd123 sample was 92.5 K and the $J_c$ at 77 K and 0 T was approximately $50kA/cm^2$. The trapped magnetic field contour and magnetic levitation forces were dependent on the top surface morphology of TSMG processed Gd123 samples. The single grain Gd123 samples, field-cooled at 77 K using a Nd-B-Fe permanent magnet with 5.27 kG and 30 mm dia., showed the trapped magnetic field contour of a single grain with a maximum of 4 kG at the sample center. The maximum magnetic levitation forces of the single grain Gd123 sample, field-cooled or zero field-cooled, were 40 N and 107 N, respectively.

• 대한기계학회논문집A
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• 제27권11호
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• pp.1941-1948
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• 2003

This paper is about feasibility study of positioning device using magnetic suspension system which uses only vertical magnetic forces. The proposed system has inherited advantages from contact-free system, simple structure, and high expansibility in operating range different from conventional positioning devices. In this paper, the structure and operating principle are described and the linearized magnetic force and dynamic model are obtained. With the linear control theory, the experiments are executed. finally, the experimental results are shown.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권11호
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• pp.604-610
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• 1999

Vibration of a rotor-bearing system driven by an electric motor is a coupled phenomenon between mechanical characteristics and magnetic origins through the air-gap. With the advent of new high-energy magnets together with high precision motor applications, magnetic sources of vibration are becoming more serious. This paper investigates the transient whirl responses of a rotor system with purely mechanical origins and compares it with that of magnetically coupled origins. A perturbation method is applied to model the magnetic field associated with rotor eccentricity. Electromagnetic forces are obtained by the Maxwell stress method, which utilizes the analytical expression of radial flux density distribution. The FEM was applied to a rotor-motor system to illustrate magnetically coupled effects in rotor dynamics. Results show that magnetically coupled sources significantly affect the vibration of the rotor-motor system.

• Journal of Power Electronics
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• 제9권2호
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• pp.243-258
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• 2009

Bearingless centrifugal pump systems are employed in the semiconductor, pharmaceutical and medical industries due to their facility for pumping high purity fluids without particle contamination. Two types of forces have to be generated by the stator units, namely bearing forces for achieving magnetic levitation, and drive forces for producing the needed pump torque. The generation of these forces requires bearing and drive windings, which can be realized as separate bearing and drive coils or as identical, combined coils on the stator claws. In this paper, a detailed comparison between these two winding concepts is undertaken, whereby the copper losses, the power electronics losses, and the achievable pump output pressure are evaluated for both concepts. For each criterion a ratio of improvement is calculated analytically which allows evaluation of the performance of the two winding concepts for any given pump operating point and design. Finally, also practical features such as control complexity, cabling effort and manufacturability are discussed and measurements on prototype systems are carried out to validate the considerations.

• 제어로봇시스템학회논문지
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• 제12권8호
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• pp.798-804
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• 2006

To overcome the limited relative uncertainty and work range of the existing planar stage and the bulk structure of the contact-less motor for rotation, the novel operating principle to realize the precise rotation is suggested. It uses the two-axial vector forces, normal force and thrust force, of three-induction type of axial motors located $120^{\circ}$ apart, resulting in the contact-free rotation of the mover. Firstly in this paper, the magnetic forces across the air gap are modeled and simulated under the various conditions. It clarifies the feasible range of the derived solution. And the algorithm compensating the strong cross couple between the forces and the control inputs; generally AC magnitude and slip frequency, is given to realize the independent control of six axes. Finally, for the successfully implemented system, the round test and the micro step test results are given.

• 한국생산제조학회지
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• 제22권6호
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• pp.1010-1017
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• 2013

Two-axial electrodynamic forces generated on a conductive plate by a partially shielded magnet wheel are strongly coupled through the rotational speed of the wheel. To control the spatial position of the plate using magnet wheels, the forces should be handled independently. Thus, three methods are proposed in this paper. First, considering that a relative ratio between two forces is independent of the length of the air-gap from the top of the wheel, it is possible to indirectly control the in-plane position of the plate using only the normal forces. In doing so, the control inputs for in-plane motion are converted into the target positions for out-of-plane motion. Second, the tangential direction of the open area of the shield plate and the rotational speed of the wheel become the new control variables. Third, the absolute magnitude of the open area is varied, instead of rotating the open area. The forces are determined simply by using a linear controller, and the relative ratio between the forces creates a unique wheel speed. The above methods were verified experimentally.