• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.367-368
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• 2016

10kV IGCT has been recently developed and has the potential to push wind turbine systems to higher power and voltage rating. Converters employing IGCTs need snubber and OVP circuit to limit the rate of current's rising and peak over voltage across IGCT during turn on and off state, respectively. The conventional RCD snubber which is used in such power converter dissipates a significant amount of power. In order to reduce the amount of energy lost by conventional RCD snubber, this paper proposes flyback type snubber comprising two coils wound on a magnetic core. The flyback snubber not only meets all of the IGCTs characteristics during on and off-state but also significantly saves the power loss. Modern magnetic model using permeance-capacitance analogy leads to more accurate loss analysis of flyback type di/dt snubber circuit in 3-level NPC type back-to-back VSC. In turns, the comparison between conventional and flyback type snubber yield the effectiveness of proposed snubber in wind turbine systems.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.700_701
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• 2009

In comparison with conventional motors, Superconducting Homopolar Synchronous Motors (SHSMs) have advantages that it generates high magnetic field by superconducting winding. Therefore, superconducting coil used in SHSM can reduce the motor size and enhance the motor efficiency for high torque applications under the space constraints for propulsion system. During the design process of SHSM, it is required to evaluate the performance of initial design model, that is accurately analyzed using 3D magnetic field modeling large air-gap and flux distribution of axial direction is properly taken into account. In this paper, we analyze magnetic field of a homopolar motor with a 4-pole homopolar rotor and a stator of 3 phase windings. The field analysis is done using 3D finite element analysis which can reflect the end effect and overhang winding. And we extract mutual inductances between a rotor wind and the 3 stator windings. The extracted inductances are used for evaluation of overall motor performances that are calculated with generalized circuit theory of electrical machines.

• 한국정밀공학회지
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• 제25권6호
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• pp.134-142
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• 2008

In this paper, we propose a precise linear motion stage supported by magnetically preloaded air bearings. The eight aerostatic bearings with rectangular carbon porous pads were located only one side of vertical direction under the platen where four bearings are in both sides of horizontal direction as wrap-around-design, and this gives simpler configuration than which constrained by air bearings for all direction. Each of the magnetic actuators has a permanent magnet generating static magnetic flux far required preload and a coil to perturb the magnetic farce resulting adjustment of air- bearing clearance. The characteristics of porous aerostatic bearing are analyzed by numerical analysis, and analytic magnetic circuit model is driven for magnetic actuator to calculate preload and variation of force due to current. A 1-axis linear stage motorized with a coreless linear motor and a linear encoder was designed and built to verify this design concept. The load capacity, stiffness and preload force were examined and compared with analysis. With the active magnetic preloading actuators controlled with DSP board and PWM power amplifiers, the active on-line adjusting tests about the vertical, pitching and rolling motion were performed. It was shown that motion control far three DOF motions were linear and independent after calibration of the control gains.

• 전기학회논문지
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• 제59권7호
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• pp.1199-1205
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• 2010

The recent power system is required to a large size of facilities and high power technology according to increasing power demand. However, it could lead to spoiling the beauty of city and environment problem. The miniaturized facilities with large capacity such as GIS have been required in recent power system. The GIS(Gas Insulated Substation) using the SF6 insulation gas enables to miniaturize facilities with large capacity with high insulation performance. However, the substation installed GIS has required to new design model which is different from the conventional substation. The TRV(Transient Recovery Voltage) analysis on simple circuit may applied by differential equation. However, in case of relatively complicated system, EMTP(Electro Magnetic Transients Program) mainly has been used to design and simulate for transient analysis. This paper mainly design the 22.9 kV GIS system and analyze the transient recovery voltage of main circuit breaker using EMTP/RV. It also enables to easily design the other substation installed GIS with same maker and voltage level because the proposed GIS model consists of separated modules such as busbar, circuit breaker, bushing, CT, PT etc. Eventually, it contributes to comfortably compare the interrupting performance of circuit breaker and system TRV corresponding to the substation system configuration.

• 전력전자학회논문지
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• 제16권2호
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• pp.137-144
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• 2011

자기공명을 이용한 무선 전력 전송 시스템의 등가회로 모델이 제시되었고, 이를 통한 설계기법이 제안되었다. 두개의 코일로 구성된 간단한 트랜스포머의 등가회로를 확장하는 방법으로 본 시스템의 노드 방정식을 세웠고, 이로부터 효율을 높이기 위한 최적의 코일간 거리를 해석하였다. 손실이 있는 경우의 주파수 특성을 계산하기 위해, 상용 설계 시뮬레이터에 등가회로 모델을 심었다. 실제 시스템의 모델 파라미터를 추출하여 시뮬레이션 결과와 측정결과를 비교하였다. 이 해석으로부터, 자기공명 방식의 무선 전력 전송 시스템이 수 미터의 거리까지 높은 효율을 보일 수 있음을 알 수 있었고, 이때 임피던스 정합이 매우 중요하다는 것을 알 수 있었다. 개발된 모델을 통해 공진 코일이 더 많이 있는 경우와 같은, 유사한 시스템의 특성을 예측할 수 있다.

• 한국자기학회지
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• 제19권1호
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• pp.5-11
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• 2009

Explosive Magnetic Generator of Frequency(EMGF)는 고폭화약의 폭발을 이용하여 화약의 폭발 에너지를 전자기 에너지로 변환 시키면서 초고주파의 강한 전자파를 발생시키는 효율적인 방법으로 연구되고 있다. 이 때 발생하는 전자파의 물리적 원인은 현재까지 명확하게 규명되어 있지 않은데, 단순한 시변 등가회로 해석만으로는 이러한 고주파 발진을 설명하기 어려운 것으로 알려져 있다. 이 논문에서는 기존에 널리 받아 들여 지고 있는 지수 감소적인 시변 인덕턴스 변화 모델에 대해서 자장압축효과를 고려한 유한요소 해석을 통해 문제점을 분석하고 보다 정확한 인덕턴스 변화 모델의 경향성에 대해서 제시하고자 한다. 그리고 이렇게 제시된 새로운 인덕턴스 변화 모델을 사용한 EMGF 출력 시뮬레이션을 통해 새로운 인덕턴스 변화 모델이 출력에 미치는 영향을 분석한다.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1025-1034
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• 2015

This paper presented an improved analytical method for calculating the open-circuit magnetic field in the surface-mounted permanent magnet machines accounting for slots and eccentric magnet pole. Magnetic field produced by radial and parallel permanent magnet is equivalent to that produced by surface current according to equivalent surface-current method of permanent magnet. The model is divided into two types of subdomains. The field solution of each subdomain is obtained by applying the interface and boundary conditions. The magnet field produced by equivalent surface current is superposed according to superposition principle of vector potential. The investigation shows harmonic contents of radial flux density can be reduced a lot by changing eccentric distance of eccentric magnet poles compared with conventional surface-mounted permanent-magnet machines with concentric magnet poles. The FE(finite element) results confirm the validity of the analytical results with the proposed model.

• 대한전기학회논문지
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• 제33권11호
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• pp.456-463
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• 1984

The fast-rising high-voltage pulse generation circuit system of a theta pinch is both theoretically and experimentally investigated. The idealized model of this circuit system is a hybrid circuit system composed of three parts: a lumped circuit part being consisted of a capacitor bank and a spark switch connected in series, another lumped circuit part being consisted of the Blumlein transmission line, whose end load is the pinch coil. the voltage difference between two ends of the pinch coil is formulated by analyzing this hybrid circuit system by means of the law of the signal propagation in the transmission line and Kirchhoff's laws. The expedient numerical method for computer calculation is developed to generate the pulse profile of the voltage difference across the pinch coil. The period of the experimentally measured main pulse is a fourth of the theoretical one neglecting the resistance of the pinch coil. We attribute this discrepancy to the modelling in the theoretical calculation that hte resistance and inductance of the spark switch and capacitor bank are assumed to be constant through discharge. Therefore, we can see that the rise time of the imploding magnetic-field pulse is mainly dependent on the spark switch and capacitor bank.

• Journal of Power Electronics
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• 제17권5호
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• pp.1298-1307
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• 2017

The constant on-time current-mode controlled (COT-CMC) switching dc-dc converter is stable, with no subharmonic oscillation in its current loop when a voltage ripple in its outer voltage loop is ignored. However, when its output capacitance is small or its feedback gain is high, subharmonic oscillation may occur in a COT-CMC buck converter with a proportional-integral (PI) compensator. To investigate the subharmonic instability of COT-CMC buck converters with a PI compensator, an accurate reduced-order asynchronous-switching map model of a COT-CMC buck converter with a PI compensator is established. Based on this, the instability behaviors caused by output capacitance and feedback gain are investigated. Furthermore, an approximate instability condition is obtained and design-oriented stability boundaries in different circuit parameter spaces are yielded. The analysis results show that the instability of COT-CMC buck converters with a PI compensator is mainly affected by the output capacitance, output capacitor equivalent series resistance (ESR), feedback gain, current-sensing gain and constant on-time. The study results of this paper are helpful for the circuit parameter design of COT-CMC switching dc-dc converters. Experimental results are provided to verify the analysis results.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.879-891
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• 2009

Impedance of rails is increased by the magnetic coupling between rails and reinforcing bars in the concrete slab track. Currently, the current of track circuit has been compensated by installing the compensation capacitors on track circuit because of increasing the impedance of rails. In case of a rapid transit railway, the compensation capacitors are installed every 20[m] to compensate the current of track circuit in the concrete slab track. Because the interval of one block for a rapid transit railway is as long as 1500[m], the compensation capacitors are installed about the number of 70$\sim$75 on track circuit. However, in case the compensation capacitors are broken over the number of three, it is a problem that the amplitude of current is under standard amplitude of current which is 0.8[A]. In this paper, it was suggested installing a compensation capacitor by using resonance phenomenon on the concrete slab track. We represent the electrical model of track circuit and the four terminal network, calculate the parameters demanded for the electrical model in the concrete slab track. Also, we computed the position and capacitance of the compensation capacitor about 2040[Hz], 2400[Hz], 2760[Hz], 3120[Hz] which currently is the track circuit frequency in the Gyeongbu rapid transit railway and demonstrated the validity of it, using the Matlab and PSpice program.