• 조명전기설비학회논문지
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• 제28권5호
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• pp.92-97
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• 2014

The SRM is a doubly salient, singly excited machine. The torque is developed by the tendency for the magnetic circuit to adopt a configuration of minimum reluctance, i.e. for the rotor to move into in line with the stator poles and to maximize the inductance of the coils excited. It is common practice to combine them into groups of poles which are excited simultaneously; for example, 8/6 SRM (8 stator poles and 6 rotor poles) for 4 phases, 6/4, 12/8 SRM for 3 phases, 4/2, 6/3 SRM for 2 phases. Small number of phases in two-phase SRMs allows more cost savings with regards to the switching devices in the converter. The stator back irons of two phase 6/3 SRM and C-core 4/3 SRM does not experience any flux reversal as the flux is in the same direction whether phase A or B is excited. In this study, the similarities, the differences, and structural characteristics between the two SRMs was studied, The magnetic analysis also has been carried out by the finite element method analysis (FEM).

• Journal of Power Electronics
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• 제13권6호
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• pp.939-954
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• 2013

The Direct Torque Control (DTC) technique for Permanent Magnet Synchronous Motors (PMSM) is receiving increased attention due to its simplicity and robust dynamic response when compared with other control techniques. The classical switching table based DTC results in large flux and torque ripples in the motors. Several studies have been reported in the literature on classical DTC. However, there are only limited studies that actually discuss or evaluate the classical DTC. This paper proposes, novel switching table / DTC methods for PMSMs to reduce torque ripples. In this paper, two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC scheme I and DTC scheme II, respectively. In both DTC schemes a simple modification is made to the classical DTC structure. The two level inverter available in the classical DTC is eliminated by replacing it with a three level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large - Zero (LZ), Medium - Zero (MZ) and Small - Zero (SZ), where as in DTC scheme II, all of the voltage vectors are considered to form a switching table. Based on these groups, a novel switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures through theory analysis and computer simulations. The superiority of the proposed DTC method is also confirmed by experimental results. It can be observed that the proposed techniques can significantly reduces the torque ripples and improves the quality of current waveform when compared with traditional and existing methods.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.343-346
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• 2000

In most inverter/converter applications SVPWM method is the preferred approach for it shows good characteristics in linear modulation range and waveform quality. in this paper we propose a new carrier based SVPWM method for multi-level system. First we survey the conventional carrier based SVPWM method and investigate the problem of the conventional one for the multi-level system with the focus on the switching frequency harmonic flux trajectories. Finally we propose a new carrier based SVPWM method that can reduce harmonic distortion. Simulation and experimental results are given for the verification of the proposed SVPWM method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.674_675
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• 2009

수치해석을 사용하여 2MVA 몰드 변압기의 정전용량을 시뮬레이션(FLUX 2D)하고 계산하였다. 산출한 정전 용량 값을 변압기 모델링 회로에 적용하여 switching surge 등 이상전압이 인가되었을 때 변압기 내부에 있는 권선들의 전압분포를 예상하고 절연설계에 적용 할 수 있음을 보였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.593-596
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• 2001

It is necessary for calculation of repulsion forces acting on the closed electric contacts flowing over-current, e.g. inrush current and overload currents, to do optimum design of switching devices. In this paper, the farces and flux densities generated by currents at the contact point when circuit breakers are in closed state are obtained by using 3D finite element methode. To be convinced of the results, we measure electrogmanetic repulsion forces on contacts by measuring voltage between opened contacts in MCCB.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 추계학술대회 논문집
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• pp.67-68
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• 2015

본 논문은 폐루프 고피나스 자속관측기의 P/PI모드를 전환하여 전환점부근 저속에서 모터상수 변동에도 강인한 센서리스 벡터제어가 가능한 전환기법을 제안하였다.

• 전력전자학회논문지
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• 제7권1호
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• pp.81-90
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• 2002

본 논문은 직접토크제어에 의한 리럭턴스 동기 전동기의 위치센서 없는 고성능 제어시스템을 제안한다. 이 시스템은 고정자 자속관측기, 속도/토크 관측기, 두 개의 디지털 히스테리시스 제어기, 최적 스위칭 룩업 테이블, IGBT 전압형 인버터, 그리고 TMS320C31 DSP보드로 구성된다. 넓은 속도 범위에서의 안정된 응답특성을 얻기 위해서 전동기 단자에서 얻어진 전압과 전류를 사용하는 폐루프 자속관측기를 사용하였다. 개발된 고성능 속도제어 시스템의 동특성을 검증하기 위해서 1.0[kW] 리럭턴스 동기 전동기를 사용하여 시뮬레이션과 실험을 수행한 결과 저속영역과 고속영역 모두 우수한 동특성을 얻을 수 있었다.

• 대한의용생체공학회:의공학회지
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• 제27권1호
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• pp.30-37
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• 2006

Injecting currents into an electrically conducting subject, we may measure the induced magnetic flux density distributions using an MRI scanner. The measured data are utilized to reconstruct cross-sectional images of internal conductivity and current density distributions in Magnetic Resonance Electrical Impedance Tomography (MREIT). Injection currents are usually provided in a form of mono-polar or bi-polar pulses synchronized with an MR pulse sequence. Given an MRI scanner performing the MR phase imaging to extract the induced magnetic flux density data, the current source becomes one of the key parts determining the signal-to-noise ratio (SNR) of the measured data. Since this SNR is crucial in determining the quality of reconstructed MREIT images, special care must be given in the design and implementation of the current source. This paper describes a current source design for MREIT with features including interleaved current injection, arbitrary current waveform, electrode switching to discharge any stored charge from previous current injections, optical isolation from an MR spectrometer and PC, precise current injection timing control synchronized with any MR pulse sequence, and versatile PC control program. The performance of the current source was verified using a 3T MRI scanner and saline phantoms.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권10호
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• pp.693-700
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• 2000

A direct torque control algorithm for 3-level inverter-fed induction motors is presented. Conventional voltage selection methods provoke some problems such as stator flux drooping phenomenon and undersirable torque control appeared especially at the low speed operation. To overcome these problems, a proposed method uses intermediate voltage vectors, which are inherently generated in 3-level inverters. In the proposed algorithm, both subdivision of the basic switching sectors and applications of tntermediated voltages improve the low speed operation characteristics. This algorithm basically considers applications in which direct torque controlled induction motors are fed by 3-level inverters with low switching frequency around 500Hz. An adaptive observer is also employed to bring better responses at the low speed operation, by estimating some state-variables, motor speed and motor parameters which take a deep effect on the performance of the low speed operation. Simulation and experiment results verify effectiveness of the proposed algorithm.

• 조명전기설비학회논문지
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• 제27권3호
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• pp.65-78
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• 2013

To analyze influences under open fault conditions in switching devices, an integrated simulation and condition monitoring scheme for a permanent magnet synchronous generator (PMSG) based variable speed grid-connected wind turbine system are presented. Among various faults in power electronics components, the open fault in switching devices may arise when the switches are destructed by an accidental over current, or a fuse for short protection is blown out. Under such a faulty condition, the grid-side inverter as well as the generator-side converter does not operate normally, producing an increase of current harmonics, and a reduction in output and efficiency. As an effective way for a condition monitoring of generation system by online basis without requiring any diagnostic apparatus, the estimation schemes for generated voltage, flux linkage, and stator resistance are proposed and the validity of the proposed scheme is proved through comparative simulations.