• Journal of Power Electronics
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• 제18권4호
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• pp.1086-1098
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• 2018

This study presents a new sensorless commutation method for brushless direct current motors to replace Hall sensor signals with virtual Hall signals. The importance of the proposed method lies in the simultaneous elimination of the phase shifter and the low-pass filters, which makes the method simple and cost-effective. The method removes high ripple switching noises from motor terminals, thereby decreasing motor losses. The proposed method utilizes unfiltered line voltages with notches caused by current commutation. Hence, specific sign signals are defined to compensate for the effects of commutation noise. The proposed method is free from phase delay that originates from low-pass filters. The method directly produces virtual Hall signals, and thus, it can be interfaced with low-cost commercial commutation integrated circuits based on Hall sensors. Simulation and experimental results show the effectiveness and validity of the proposed method.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.65-68
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• 2001

In the vector control methods of induction motor, the stator current is divided into the flux and torque component current. By controlling these components respectively, the methods control independently flux and torque as in the DC motor and improve the control effects. To apply the vector control methods, the position of the rotor current is identified. The indirect vector control use the parameters of the machine to identify the position of rotor flux. But due to the temperature rise during machine operation, the variation of rotor resistance degrades the vector control. To solve the problem, the q-axis is aligned to reference frame without phase difference by comparing the real flux component with the reference flux component. Then to compensate the slip, PI controller is used. The proposed method keeps a constant slip by compensating the gain of direct slip frequency when the rotor resistance of induction motor varies. To prove the validations of the proposed algorithm in the paper, computer simulations is executed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.125-128
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• 2006

This paper presents a novel type soft switching PWM power frequency AC-AC converter using bidirectional active switches or single phase utility frequency AC-high frequency AC matrix converter. This converter can directly convert utility frequency AC (UFAC, 50Hz/60Hz) power to high frequency AC (HFAC) power ranging more than 20kHz up to 100kHz. A novel soft switching PWM prototype of high frequency multi-resonant PWM controlled UFAC-HFAC matrix converter using antiparallel one-chip reverse blocking IGBTs manufactured by IXYS corp. is based on the soft switching resonance with asymmetrical duty cycle PWM strategy. This single phase UFAC-HFAC matrix converter has some remarkable features as electrolytic capacitor DC busline linkless topology, unity power factor correction and sine-wave line current shaping, simple configuration with minimum circuit components, high efficiency and downsizing. This series load resonant UFAC-HFAC matrix converter, incorporating bidirectional active power switches is developed and implemented for high efficiency consumer induction heated food cooking appliances in home uses and business-uses. Its operating performances as soft switching operating ranges and high frequency effective power regulation characteristics are illustrated and discussed on the basis of simulation and experimental results.

• Smart Structures and Systems
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• 제2권3호
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• pp.209-224
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• 2006

The use of smart dampers to optimally control the response of structures is on the increase. To maximize the potential use of such damper systems, their accurate modeling and assessment of their performance is of vital interest. In this study, the performance of a controllable fluid dashpot damper, in terms of damper forces, damper dynamic range and damping force hysteretic loops, respectively, is studied mathematically. The study employs a damper Bingham-Maxwell (BingMax) model whose mathematical formulation is developed using a Fourier series technique. The technique treats this one-dimensional Navier-Stokes's momentum equation as a linear superposition of initial-boundary value problems (IBVPs): boundary conditions, viscous term, constant Direct Current (DC) induced fluid plug and fluid inertial term. To hold the formulation applicable, the DC current level to the damper is supplied as discrete constants. The formulation and subsequent simulation are validated with experimental results of a commercially available magneto rheological (MR) dashpot damper (Lord model No's RD-1005-3) subjected to a sinusoidal stroke motion using a 'SCHENK' material testing machine in the Materials Laboratory at the University of Technology, Sydney.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.1114-1116
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• 2000

A direct model reference adaptive control (DMRAC) is applied to the speed control of brushless do(BLDC) motor. The main objective is to achieve precise speed control in the face of varying motor parameters and load. The control is described as an outer loop speed control and an inner current loop control which has raster dynamics than the speed loop. The adaptive control is applied to the outer speed control loop. DMRAC is compared to an indirect adaptive controller(IMRAC) and a PI controller. Simulation results show that the two adaptive controllers give similar respose and are superior to the PI controller. However, the DMRAC algorithm is simpler to implement.

• 한국세라믹학회지
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• 제51권5호
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• pp.375-379
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• 2014

Nanocrystalline TiAlN coatings were prepared by reactively sputtering TiAl metal target with $N_2$ gas. This was done using a magnetron sputtering system operated in DC and ICP (inductively coupled plasma) conditions at various power levels. The effect of ICP power (from 0 to 300 W) on the coating microstructure, corrosion and mechanical properties were systematically investigated using FE-SEM, AFM and nanoindentation. The results show that ICP power has a significant influence on coating microstructure and mechanical properties of TiAlN coatings. With increasing ICP power, the coating microstructure evolved from the columnar structure typical of DC sputtering processes to a highly dense one. Average grain size of TiAlN coatings decreased from 15.6 to 5.9 nm with increasing ICP power. The maximum nano-hardness (67.9 GPa) was obtained for the coatings deposited at 300 W of ICP power. The smoothest surface morphology (Ra roughness 5.1 nm) was obtained for the TiAlN coating sputtered at 300 W ICP power.

• Journal of electromagnetic engineering and science
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• 제14권1호
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• pp.25-30
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• 2014

This paper discusses the design of a high frequency Greinacher voltage multiplier as rectifier; it has a greater conversion efficiency and higher output direct current (DC) voltage at high power compared to a simple halfwave rectifier. Multiple diodes in the Greinacher voltage multiplier with distributed circuits consume excited power to the rectifier equally, thereby increasing the overall power capacity of the rectifier system. The proposed rectifiers are a Greinacher voltage doubler and a Greinacher voltage quadrupler, which consist of only diodes and distributed circuits for high frequency applications. For each rectifier, the RF-to-DC conversion efficiency and output DC voltage for each input power and load resistance are analyzed for the maximum conversion efficiency. The input power with maximum conversion efficiency of the designed Greinacher voltage doubler and quadrupler is 3 and 7 dB higher, respectively;than that of the halfwave rectifier.

• 자원환경지질
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• 제34권5호
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• pp.499-506
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• 2001

연안지역에서 해수의 지하 유동현상을 효과적이고 경제적으로 파악하기 위하여 등위치 송수신루프배열의 시간영역 전자탐사법(Time-domain Electromagnetic :TEM)을 이용한 지구물리모니터링을 적용하였다. TEM 모니터링은 전기 비저항 모니터링과 비교하여 해수유동에 대한 TEM반응의 민감도는 떨어진다. 그러나, 광범위한 조사지역에 대한 담수-해수 전이대의 공간적인 분포를 파악하는데 있어서는 측정시간을 포함한 탐사경비 그리고 현장에서 자료처리 측면에서 볼 때 매우 효율적이다.

• 한국전기화학회:학술대회논문집
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• 한국전기화학회 2005년도 수소연료전지공동심포지움 2005논문집
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• pp.383-390
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• 2005

Effect of applying a DC voltage on the interfacial reaction at the metal to zirconia interface was investigated utilizing an oxygen ionic conductivity of partially stabilized zirconia. The joining of copper rod and zirconia tube was carried out in Ar gas atmosphere at $1000^{\circ}C$. There are two type of the joining. The one is the reaction bond consisting of copper and zirconia was dominated by surface reaction with a undetectable very thin layer. It was found that copper elements were diffused to zirconia side, but that Zr ions were not diffused to copper side. These results mean application of a DC voltage to migrate oxygen to the copper-zirconia interface can oxidize metal at the copper-zirconia interface and the bonding reaction between zirconia and copper oxide may occur. The other is the reaction bonding was dominated by interdiffusion with a very thick interface layer. This result mean application of a DC voltage can reduce zirconia at the interface. The bonding reaction is to be an alloying between Zr and Cu.

• 전기학회논문지
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• 제65권4호
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• pp.601-610
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• 2016

The light-emitting diode (LED) has been used in a variety of industrial fields and for general 0lighting purposes on account of its high efficiency, low power consumption and long lifespan. The LED is driven by direct current; therefore, an AC/DC converter is typically required for its use. An electrolytic capacitor is generally used for stabilizing DC voltage during use of the AC/DC converter. However, this capacitor has a short lifespan, which makes it a limiting factor in LED lighting. Furthermore, LED lighting requires a dimmable control to enable energy savings and fulfil a growing consumer demand. In this paper, the dimmable single-stage power factor correction (PFC) continuous conduction mode (CCM) flyback converter that employs no electrolytic capacitor is presented. The LC resonant filter is alternatively applied to reduce the 120[Hz] ripple on the output. And the optimum value of the LC resonant filter parameters considering both efficient and performance is analysed. Simulation and experimental results verify the satisfactory operation of the converter.