• Proceedings of the KIEE Conference
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• 2003.10b
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• pp.128-130
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• 2003

For electrical machine designers, core loss data are usually provided in the form of tables or curves of total loss versus flux density or frequency. The aim of this work is to propose a mathematical model for the iron losses prediction in soft magnetic material$ with any frequency and flux density. In this paper, three formulas for calculating the iron loss coefficients are discussed. And the coefficients are applied to calculate the iron loss of the 25kW high speed motor.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.140-142
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• 1997

After finding the harmonic components by measuring the thrust force, which affects high accuracy position control during micro-step drive of LPM, the exciting current was calculated to remove them. Also the detent force being induced by magnetic flux density of permanent magnetic was measured. It was comfirmed that the tooth and slot width was designed properly thresh the analysis of detent force.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.19-21
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• 1997

This paper treated a new method that generates the dipole magnetic field for high speed machines by using Halbach array, which was suggested by Klaus Halbach. The Halbach array can produce the various field distribution without magnetic materials. Therefore, the iron losses can be reduced. This paper presented the magnetic characteristics on both linear and cylindrical Halbach array. And the Halbach array for dipole field was manufactured with Nd-Fe-B magnets having 1.17(T), the measured flux density was compared the theoretical values acquired by three dimensional FEM analysis. Finally, the magnetic characteristics of Halbach array were compared with those of other conventional dipole field systems.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.11
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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.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.918-920
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• 2001

PMSM drives are widely used in industrial and residential applications because of high efficiency, high power density and high performance. For better performance of PMSM, however, torque ripples should be reduced. This paper investigates a reduction of torque ripple due to the unsinusoidal flux linkage produced by the shapes of stator slot and magnetic pole. To minimize torque ripple, a simple flux estimator is proposed. This method iteratively compensates the distributed flux linkage from an error between the measured and estimated currents. The proposed algorithm is verified through simulation.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.201-206
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• 2004

The AC-DC magnetic field standard systems were constructed for the calibration of magnetometers for low magnetic field and the tests for low magnetic field characteristics of sensors and materials. In the range of 1 mT, the expanded uncertainty of dc is 8${\times}$10$\^$-6/, ac uncertainties are 0.16% in 0.1～1 kHz, 0.26% in 1～5 kHz, and 0.44% in 5～20 kHz. We have been participated in international key comparison(KC) to achieve the equality and the mutual agreement between standard institutes for the results of calibrations and tests. KRISS participating in ac-dc magnetic flux density of KC got equal level of uncertainty results compare with the advanced nations. It confirm that measurement ability of magnetic flux density is high level in the world.

• Proceedings of the KIPE Conference
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• 2012.11a
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• pp.31-32
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• 2012

This paper presents a new design of magnetic bearing structure for application in Nuclear Power Plant (NPP). The proposed design includes so-called saturated coils which is used to generate the bias flux for bearing almost the whole mass of the rotor, and so-called linear auxiliary coil controlled to stabilize the suspension. The saturated coil is considered as an special electromagnet which is controlled to operate in the region of magnetic saturation in order to minimize the bias current as well as to enhance the magnetic flux density. This strategy will result in a very compact size of magnetic bearing as well as increasing the speed of the response of the current controller. The novel structure is expected to be applied to design very high power gas turbine generator of next generation of fast reactor in which the mass of rotor can reach 50 tons. The total power of the NPP can reach 2,000 MW. Moreover, the issue of arc occurrence between coils is also discussed and two solutions are proposed.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1075-1080
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• 2015

A hybrid electric vehicle (HEV) powertrain has more than one energy source including a high-voltage electric battery. However, for a high voltage electric battery, the average current is relatively low for a given power level. Introduced to increase the voltage of a HEV battery, a compact, high-efficiency boost converter, sometimes called a step-up converter, is a dc-dc converter with an output voltage greater than its input voltage. The inductor occupies more than 30% of the total converter volume making it difficult to get high power density. The inductor should have the characteristics of good thermal stability, low weight, low losses and low EMI. In this paper, Mega Flux^® was selected as the core material among potential core candidates. Different structured inductors with Mega Flux^® were fabricated to compare the performance between the conventional air cooled and proposed potting structure. The proposed inductor has reduced the weight by 75% from 8.8kg to 2.18kg and the power density was increased from 15.6W/cc to 56.4W/cc compared with conventional inductor. To optimize the performance of proposed inductor, the potting materials with various thermal conductivities were investigated. Silicone with alumina was chosen as potting materials due to the high thermo-stable properties. The proposed inductors used potting material with thermal conductivities of 0.7W/m·K, 1.0W/m·K and 1.6W/m·K to analyze the thermal performance. Simulations of the proposed inductor were fulfilled in terms of magnetic flux saturation, leakage flux and temperature rise. The temperature rise and power efficiency were measured with the 40kW boost converter. Experimental results show that the proposed inductor reached the temperature saturation of 107℃ in 20 minutes. On the other hand, the temperature of conventional inductor rose by 138℃ without saturation. And the effect of thermal conductivity was verified as the highest thermal conductivity of potting materials leads to the lowest temperature saturations.

• Journal of Biomedical Engineering Research
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• v.30 no.2
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• pp.179-184
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• 2009

Magnetic Resonance Electrical Impedance Tomography (MREIT) is a new bio-imaging modality providing cross-sectional conductivity images from measurements of internal magnetic flux densities produced by externally injected currents. Recent MREIT studies demonstrated successful conductivity image reconstructions of postmortem and in vivo canine brain. However, the whole head imaging was not achieved due to technical issues related with electrodes and noise in measured magnetic flux density data. In this study, we used a new carbon-hydrogel electrode with a large contact area and injected 30 mA imaging current through a canine head. Using a 3T MREIT system, we performed a postmortem canine experiment and produced high-resolution conductivity images of the entire canine head. Collecting magnetic flux density data inside the head subject to multiple injection currents, we reconstructed cross-sectional conductivity images using the harmonic $B_z$ algorithm. The conductivity images of the canine head show a good contrast not only inside the brain region including white and gray matter but also outside the brain region including the skull, temporalis muscle, mandible, lingualis proprius muscle, and masseter muscle.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.5
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• pp.253-259
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• 2005

Magnetic encoder with relatively low pulse per rotation is generally used for detecting speed of the high-speed rotating machine. It is due to the fact of the mechanical problems of vibration and bearing stiffness and also the limit of maximum output pulse of the mounted encoder. The magnetic encoder is divided into two types, that is, toothed gear-wheel method and magnetic wheel method according to the shape of the rotation disk. In case of detecting speed by the tooth gear-wheel, the encoder itself can be acted as the additional inertia where the number of tooth determining the output pulse and the width of the wheel detecting the change of the magnetic flux density are relatively enough large considering the volume of the rotating machine. While the magnetic wheel method has the limit of the magnetizing number of the ring magnet, there is relatively few, if nv, the influence of inertia on the machine. In this paper, it is proposed a simple magnetic wheel encoder suited for the high speed rotating machine and the method of signal processing and the output characteristics are examined through the V/F operation of max 48,000(rpm) and 2.4(KW) spindle motor.