• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.4
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• pp.351-358
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• 2003

This paper describes distribution characteristics of switching surge voltage in stator windings of induction motor driven by IGBT PWM inverter. To analyze the voltage distribution between the turns and coils of stator winding, equivalent circuit model of induction motor including cable was proposed and high frequency parameter is computed by using finite-element method (FEM). From the electro-magnetic transient program (EMTP) simulation of the whole system for induction motor, feeder cable, and PWM inverter, the variable effect on rising time of the inverter, cable length, and switching frequency on the voltage distribution is also presented. In order to experiment, an induction motor, 380[V], 50[HP], with taps from one phase are built to consider the voltage distribution so that these results can be helpful when filter was designed to remove high dv/dt.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1678-1687
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• 2013

This paper describes a prototype of 3-phase 3.3kV/220V 6kVA modular semiconductor transformer developed in the lab for feasibility study. The developed prototype is composed of three single-phase units coupled in Y-connection. Each single-phase unit with a rating of 1.9kV/127V 2kVA consists of a high-voltage high-frequency resonant AC-DC converter, a low-voltage hybrid-switching DC-DC converter, and a low-voltage hybrid-switching DC-AC converter. Also each single-phase unit has two DSP controllers to control converter operation and to acquire monitoring data. Monitoring system was developed based on LabView by using CAN communication link between the DSP controller and PC. Through various experimental analyses it was verified that the prototype operates with proper performance under normal and sag condition. The system efficiency can be improved by adopting optimal design and replacing the IGBT switch with the SiC MOSFET switch. The developed prototype confirms a possibility to build a commercial high-voltage high-power semiconductor transformer by increasing the number of series-connected converter modules in high-voltage side and improving the performance of switching element.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.276-278
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• 2006

The switching characteristics of magnetic tunnel junctions (MTJs) comprising amorphous ferromagnetic CoFeSiB free layer have been investigated. CoFeSiB was used for the free layer to enhance the switching characteristics. The typical junction structure was $Si/SiO_{2}/Ta$ 45/Ru 9.5/IrMn 10/CoFe $7/AlO_{x}/CoFeSiB\;(t)/Ru\;60\;(in\;nm)$. CoFeSiB has low saturation magnetization ($M_{s}$) of $560\;emu/cm^{3}$ and high anisotropy constant ($K_{u}$) of $2800\;erg/cm^{3}$. These properties caused low coercivity ($H_{c}$) and high sensitivity in MTJs, and it also confirmed in submicrometer-sized elements by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. By increasing CoFeSiB free layer thickness, the switching characteristics became worse due to increase of the demagnetization field.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.3
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• pp.64-72
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• 2003

Comparing with transmission networks, the faults in distribution networks more often occurs because of the complicated structure and the adjacency to customers. Moreover the faults give direct damage to customers. So fault diagnosis and blackout restoration in distribution networks are very important elements to reduce the damage of customers and to maintain the stability. The restoration problem of distribution networks is subject to time. Minimizing the switching numbers in restoration process is the crucial element. In other words. the best restoration is to restore all blackout area through just one switching, if not the restoration has to be accomplished through several switching. This paper proposes the efficient restoration system in distribution networks to minimize the switching numbers. The proposed system uses the dynamic division method of hierarchical structure which consists of heuristic searching method and meta algorithm. The proposed system is applied to the sample networks, and the results showed a promising possibility.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.435-440
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• 2001

Piezoelectric solids such as PZT and PLZT have been widely used as sensors and actuators for various smart systems. One of the problems arising in actuator applications is that a larger actuation force needs to be produced from a small system. This naturally leads to local electric field or stress concentration and thereby resulting in a nonlinear behavior inside the system, Hence, it becomes more important to predict the nonlinear behavior of piezoelectric solids. In this paper we investigate the mechanism of nonlinear behavior in those materials and suggest a constitutive and finite element model. The calculation results obtained from the model seem to be qualitatively consistent with experiments.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.28B no.11
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• pp.859-865
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• 1991

The paper proposes a design of high-speed dynamic CMOS PLA (Programmable Logic Array) which performs stable circuit operation. The race problem which nay occur in a NOR-NOR implementation of PLA is free in the proposed dynamic CMOS PLA by delaying time between the clocks to the AND- and to the OR-planes. The delay element has the same structure as the product line of the longest delay in the AND p`ane. Therefore it is unnecessary to design the delay element or to calculate correct delay time. The correct delay generated by the delay element makes the dynamic CMOS PLA to perform correct and stable circuit operation. Theproposed dynamic CMOS PLA has few variation of switching delay with the increasing number of inputs or outputs in PLA. It is verified by SPICE circuit simulation that the proposed dynamic CMOS PLA has the better performance over existing dynamic CMOS PLA's.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.2 s.302
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• pp.49-58
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• 2005

A new soft switching three-phase PWM rectifier with simple circuit configuration and high efficiency has been developed. The proposed circuit is a kind of the auxiliary resonant commutated Pole(ARCP)converter The conventional ARCP converter requires three-auxiliary reactors and six-auxiliary switches for the soft switching auxiliary circuit and for these switching elements, a gate drive circuit and a control circuit are required, resulting in high part as a disadvantage. In the main circuit proposed in this paper, the auxiliary soft switching circuit is composed of two-auxiliary reactors, two-auxiliary switches and several diodes. In addition, common use of the PWM control circuit for two-switches will make the control circuit of the auxiliary switches simple. By means of function of the soft switching auxiliary circuit, the main switching element performs zero voltage switching operation and the auxiliary switches perform the zero current switching. In this paper, the circuit configuration and the operational analysis of the proposed circuit are described at first and then, experimental results will be reported. By using a prototype with 5[kW] capacity, the conversion efficiency of maximum $98.8[\%]$ and the power factor of $99[\%]$ or higher were obtained.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.99-99
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• 2013

In this talk, I will present two research works in progress, which are: i) mapping of piezoelectric polarization and associated charge density distribution in the heteroepitaxial InGaN/GaN multi-quantum well (MQW) structure of a light emitting diode (LED) by using inline electron holography and ii) in-situ observation of the polarization switching process of an ferroelectric Pb(Zr1-x,Tix)O3 (PZT) thin film capacitor under an applied electric field in transmission electron microscope (TEM). In the first part, I will show that strain as well as total charge density distributions can be mapped quantitatively across all the functional layers constituting a LED, including n-type GaN, InGaN/GaN MQWs, and p-type GaN with sub-nm spatial resolution (~0.8 nm) by using inline electron holography. The experimentally obtained strain maps were verified by comparison with finite element method simulations and confirmed that not only InGaN QWs (2.5 nm in thickness) but also GaN QBs (10 nm in thickness) in the MQW structure are strained complementary to accommodate the lattice misfit strain. Because of this complementary strain of GaN QBs, the strain gradient and also (piezoelectric) polarization gradient across the MQW changes more steeply than expected, resulting in more polarization charge density at the MQW interfaces than the typically expected value from the spontaneous polarization mismatch alone. By quantitative and comparative analysis of the total charge density map with the polarization charge map, we can clarify what extent of the polarization charges are compensated by the electrons supplied from the n-doped GaN QBs. Comparison with the simulated energy band diagrams with various screening parameters show that only 60% of the net polarization charges are compensated by the electrons from the GaN QBs, which results in the internal field of ~2.0 MV cm-1 across each pair of GaN/InGaN of the MQW structure. In the second part of my talk, I will present in-situ observations of the polarization switching process of a planar Ni/PZT/SrRuO3 capacitor using TEM. We observed the preferential, but asymmetric, nucleation and forward growth of switched c-domains at the PZT/electrode interfaces arising from the built-in electric field beneath each interface. The subsequent sideways growth was inhibited by the depolarization field due to the imperfect charge compensation at the counter electrode and preexisting a-domain walls, leading to asymmetric switching. It was found that the preexisting a-domains split into fine a- and c-domains constituting a $90^{\circ}$ stripe domain pattern during the $180^{\circ}$ polarization switching process, revealing that these domains also actively participated in the out-of-plane polarization switching. The real-time observations uncovered the origin of the switching asymmetry and further clarified the importance of charged domain walls and the interfaces with electrodes in the ferroelectric switching processes.

• Journal of Magnetics
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• v.12 no.1
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• pp.35-39
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• 2007

A highly sensitive magnetic sensor using the Giant MagnetoImpedance effect has been developed. The sensor performance is studied and estimated. The sensor circuitry consists of a square wave generator (driving source), a sensing element in a form of composite wire of a 25 $\mu$m copper core electrodeposited with a thin layer of soft magnetic material ($Ni_{80}Fe_{20}$), and two amplifier stages for improving the gain, switching mechanism, scaler circuit, an AC power source driving the permeability of the magnetic coating layer of the sensing element into a dynamic state, and a signal pickup LC circuit formed by a pickup coil and an capacitor. Experimental studies on sensor have been carried out to investigate the key parameters in relation to the sensor sensitivity and resolution. The results showed that for high sensitivity and resolution, the frequency and magnitude of the ac driving current through the sensing element each has an optimum value, the resonance frequency of the signal pickup LC circuit should be equal to or twice as the driving frequency on the sensing element, and the anisotropy of the magnetic coating layer of the sensing wire element should be longitudinal.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.5
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• pp.81-86
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• 2014

A smart phone subscriber needs wide bandwidth services for more fast data communication on the internet. The conventional MIMO system is now developing to resolve these problems with limited device space for antenna and frequency band environment reserved. One of way to make it practically is to add the number of antennas theoretically. But it is difficult to increase the antenna element as a limited space on the system. Therefore an active beam forming scheme is known as a way of constructing a Compact MIMO system for that. In this paper, the fast switching control block was suggested to adjust a reactance of the antenna element and verified experimentally the effects by switching signal on an orthogonal beam forming through a spatial domain.