• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.253-255
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• 2004

Conventional magnetic levitation systems could show unsatisfactory performance under air-gap disturbance due to rail irregularities. In this paper, we propose a feedback control system with discrete Kalman filter for air-gap disturbance attenuation. It is shown that excellent system performance can be obtained with the use of discrete Kalman filter, and that results from experiments agree well with those of simulations.

• 전기의세계
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• 제29권10호
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• pp.660-666
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• 1980

The finite leement method is a effetive analysis technique for obtaining approximate solutions of continuum problems with boundary conditions. This paper deals with the programming for the application of this method and the preciser analysis of the magnetic field in the air gap of the linear stepper motor by the method. The finite element analysis based on the variational principle is adopted and the computer program for reducing input data and a large number of the memory words required by the system matrix is presented. The 2-dimensional analysis of the air gap is made and several cases according to varying the position are considered.

• Transactions on Electrical and Electronic Materials
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• 제16권1호
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• pp.37-41
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• 2015

The most common structure of the current transformer (CT) consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. Therefore, the primary circuit of CT consists of a single turn of the conductor, with a secondary circuit of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry the current through the magnetic core. However, when the large current flows into a wire, it is difficult to measure its magnitude of current because the core is saturated and the core shows magnetic nonlinear characteristics. Therefore, we proposed a newly designed CT which has an air gap in the core to decrease the generated magnetic flux. Adding the air gap in the magnetic path increases the total magnetic reluctance against the same magnetic motive force (MMF). Using a ferrite core instead of steel also causes the generation of low magnetic flux. These features can protect the magnetic saturation of the CT core compared with the steel core. This technique can help the design of the CT to obtain a special shape and size.

• 조명전기설비학회논문지
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• 제25권2호
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• pp.137-142
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• 2011

In this paper, the fault current limiting and the hysteresys characteristics of a superconducting fault current limiter (SFCL) using magnetic coupling of two coils on the iron core with an air-gap were analyzed. The introduction of the air-gap in the SFCL with magnetically coupled two coils can suppress the saturation of the iron-core and, on the other hand, make the limiting impedance of the SFCL decreased, which results from the increase of the exciting current. To analyze the effect of the aig-gap on the fault current limiting characteristics of the SFCL, the hysteresys curves of the iron core comprising the SFCL were derived from the short-circuit experiment and the variation in the voltage-current trace of the SFCL during the fault period was analyzed. Through the comparison with the current limiting characteristics of the SFCL without air-gap, the air-gap could be confirmed to contribute to the suppression of the iron core's saturation through the increase of the SFCL's burden from the short-circuit current.

• 전기학회논문지
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• 제58권2호
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• pp.278-284
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• 2009

The global force and interaction body force density were evaluated in permanent magnets by using the virtual air-gap scheme incorporating the finite-element method. Until now, the virtual air-gap concept has been successfully applied to calculate a contact force and a body force density in soft magnetic materials. These force calculating methods have been called as generalized methods such as the generalized magnetic charge force density method, the generalized magnetizing current force density method, and the generalized Kelvin force density method. For permanent magnets, however, there have been few research works on a contact force and a force density field. Unlike the conventional force calculating methods resulting in surface force densities, the generalized methods are novel methods of evaluating body force density. These generalized methods yield the actual total force, but their distributions have an irregularity, which seems to be random distributions of body force density. Inside permanent magnets, however, a smooth pattern was obtained in the interaction body force density, which represents the interacting force field among magnetic materials. To evaluate the interaction body force density, the intrinsic force density should be withdrawn from the total force density. Several analysis models with permanent magnets were tested to verify the proposed methods evaluating the interaction body force density and the contact force, in which the permanent magnet contacts with a soft magnetic material.

• 전기학회논문지
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• 제58권5호
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• pp.929-935
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• 2009

As modem industrialized society progresses, the demand for electric power is increasing rapidly. The electric power system is getting amazingly bigger and complicated, which can easily induce serious troubles from the potential of large fault problems and/or system failure. The monitoring and diagnosis of the electric machine for the fault detection and protection has been important part in the electric power system. Most faults in the generator appear in the winding. This paper presents the air-gap magnetic flux characteristic of a small-scale 2-pole synchronous generator according to the faults in the field winding to protect the generator from the fault. The magnetic flux patterns in air-gap of a generator under various fault conditions as well as a normal state are simulated by using finite element method. These results are successfully applied to the detection and diagnosis of the short-circuit condition in rotor windings of a high capacitor generator.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2007년도 추계학술발표대회 및
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• pp.17.2-17.2
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• 2007

• 동력기계공학회지
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• 제16권3호
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• pp.64-68
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• 2012

Because the magnetic bearing supports levitating body without contact, wear, noise and vibration are very small comparing with mechanical bearings, it is very useful to high revolution machinery. In general, the magnetic attractive force function that is proportional to square of control current(x), and inversely proportional to square of an air gap(i) has been widely used. This paper proposed the new magnetic attractive force function that is proportional to cube of the control current, and inversely proportional to square of the air gap. The function was optimized to minimize the cost function that is the percentage of deviation about the change of a proportional constant(k), using the experimental data, ie, control currents and air gaps.

• Journal of the Optical Society of Korea
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• 제19권6호
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• pp.575-585
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• 2015

Magnetic field in magnetic bearings is the physical medium to realize magnetic levitation, the distribution of the magnetic field determines the operating performance of magnetic bearings. In this paper, a thin-slice Fiber Bragg Grating-Giant Magnetostrictive Material magnetic sensor used for the air gap of magnetic bearings was proposed and tested in the condition of dynamic magnetic field. The static property of the sensor was calibrated and a polynomial curve was fitted to describe the performance of the sensor. Measurement of dynamic magnetic field with different frequencies in magnetic bearings was implemented. Comparing with the finite element simulations, the results showed the DC component of the magnetic field was detected by the sensor and error was less than 5.87%.

• Journal of Power Electronics
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• 제16권5호
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• pp.1773-1780
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• 2016

This paper proposes a wide air-gap control method for the multi-module permanent magnet linear synchronous motor (MM-PMLSM) based on independent vector control. In particular, the MM-PMLSM consists of symmetrical multi-module and multi-phase structures, which are basically three-phase configurations without a neutral point, unlike conventional three-phase machines. In addition, there are no additional magnetic levitation windings to control the normal force of the air-gap between each stator and mover. Hence, in this paper, a dq-axis current control applying a d-q transformation and an independent vector control are proposed for the air-gap control between the two symmetric stators and mover of the MM-PMLSM. The characteristics and control performance of the MM-PMLSM are analyzed under the concept of vector control. As a result, the proposed method is easily implemented without additional windings to control the air-gap and the mover position. The effectiveness of the proposed independent vector control algorithm is verified through experimental results.