• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.784-785
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• 2015

This paper proposes a new structure of coil to maximize the conductor occupting ratio(conductor cross sectional area than the cross sectional area inside the slot) of the magnetic core. Further, assuming a case in which the 3-D coil is applied to a real motor. Analyze the current density distribution of the coil conductor by electromagnetic analysis method. Finally the AC resistance was measured according to the frequency of the coils. This expereiment is to calculate a optimal operating frequency to obtain high efficiency operational frequency range of motor.

• Journal of electromagnetic engineering and science
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• v.6 no.2
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• pp.92-97
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• 2006

In this paper, a fully integrated Ku-band tripler differential MMIC voltage controlled oscillator(VCO), which consists of a differential VCO core and two triplers, is developed using high linearity InGaP/GaAs HBT technology. The VCO core generates an oscillation frequency of 3.583 GHz, an output power of 3.65 dBm, and a phase noise of -96.7 dBc/Hz at 100 kHz offset with a current consumption of 30 mA at a supply voltage of 2.9 V. The tripler shows excellent side band rejection of 23 dBc at 3 V and 12 mA. The tripler differential MMIC VCO produces an oscillation frequency of 10.75 GHz, an output power of -13 dBm and a phase noise of -89.35 dBc/Hz at 100 kHz offset.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.373-381
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• 2000

The flow and heat transfer characteristics on the impingement surface can be controlled by the change of vortex with the acoustic excitation, because the flow characteristics of an impinging jet are affected strongly by the vortices formed at the jet exit. To investigate the effects of acoustic excitation, we measured the velocity, turbulent intensity distributions for the free jet and local heat transfer coefficients on a impingement surface. As the acoustic excitation, subharmonic frequency of excited frequency plays an important role to the control of the jet flow. If the vortex pairings are promoted by the acoustic excitation, turbulence intensity of the jet flow is increased quickly. On the other hand if the vortex pairings are suppressed, the jet flow has low turbulence intensity at the center of the jet. Therefore, the low heat transfer rates are obtained on the impingement plate for a small nozzle-to-plate distance. However, it has high heat transfer rates at a large distance between the nozzle and plate due to the increasing of potential-core length.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.4
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• pp.506-510
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• 2016

A triple-band (TB) oscillator was implemented in the TSMC $0.18{\mu}m$ 1P6M CMOS process, and it uses a cross-coupled nMOS pair and two shunt $4^{th}$ order LC resonators to form a $6^{th}$ order resonator with three resonant frequencies. The oscillator uses the varactors for band switching and frequency tuning. The core current and power consumption of the high (middle, low)- band core oscillator are 3.59(3.42, 3.4) mA and 2.4(2.29, 2.28) mW, respectively at the dc drain-source bias of 0.67V. The oscillator can generate differential signals in the frequency range of 8.04-8.68 GHz, 5.82-6.15 GHz, and 3.68-4.08 GHz. The die area of the triple-band oscillator is $0.835{\times}1.103mm^2$.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1467-1476
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• 2019

Grid unbalanced faults can cause core saturation of power transformer and produce lower-order harmonics. These issues increase the electrical stress of power electronic devices and can cause a tripping of an entire HVDC system. In this paper, based on the positive-sequence and negative-sequence impedance model of a VSC-HVDC system as seen from the point of common connection (PCC), the resonance problem is analyzed and the factors determining the resonant frequency are obtained. Furthermore, to suppress over-voltage and over-current during resonance, a novel method using a virtual harmonic resistor is proposed. The virtual harmonic resistor emulates the role of a resistor connected in series with the commutating inductor without influencing the active and reactive power control. Simulation results in PSCAD/EMTDC show that the proposed control strategy can suppress resonant over-voltage and over-current. In addition, it can be seen that the proposed strategy improves the safety of the VSC-HVDC system under unbalanced faults.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.95-100
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• 2022

In this paper, a power loss analysis technique of a high-frequency transformer of a bidirectional DAB (Dual Active Bridge) converter is reported. To miniaturize the transformer of the dual active bridge converter, a resonant inductor was designed with an air gap included low-coupled rate state core to combine leakage inductor with the resonant inductor which is required for soft-switching. In this paper, leakage inductance and magnetizing inductance, core material, type of winding and winding method are included in the dual active bridge transformer loss analysis process to enable optimal design at the initial design stage. Transformer loss analysis for dual active bridge with a switching frequency of 200 kHz and maximum output of 5 kW was executed, and elements necessary for design based on the number of turns on the primary side were graphed while maintaining the transformer turns ratio and window area. In particular, it was possible to determine the optimal number of turns and thickness of the transformer, and ultimately, the total loss of the transformer could be estimated.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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• pp.339-343
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• 2006

We observed the application possibility of inductive coupler for the underground high-voltage power line communication by means of analysis of signal transmission characteristics and magnetic properties on annealing temperatures for high-permeability Fe-base amorphous alloys. The best electromagnetic and transmission characteristics were shown in nano-crystalline precipitated alloy annealed at temperature $510^{\circ}C$. The transmission characteristics in the low-frequency band depend on permeability of magnetic core materials and its properties of high-frequency band can be improved by impedance matching. Using the high pass filter embedded in the coupler, other noise signal band except for communication signals could be cut off.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.652-655
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• 2001

Power transformers are increasingly becoming more significant in the advancement of electronic equipment. A high-performance, low-cost core material is necessary in order th come up with power transformers in the smallest and lightest scale possible and with low power requirements. In this study, we added V$_2$O$_{5}$ and CaCo$_3$to Mn-Zn ferrite to produce a high-performance low-cost core material. The compositions used were MnO : ZnO : Fe$_2$O$_3$= 37 : 11 : 52 mol%. The materials were sintered at 125$0^{\circ}C$ for three hours. Initial permeability was measured at 0.1MHz. At 200mT, power loss was measured by changing the temperature at 25KHz, 50KHz, 100KHz. When we added 0.lwt% and 0.1%wt% of V$_2$O$_{5}$와 CaCo$_3$, respectively we obtained 405 405KW/㎥ at 200mT, 100KHz, 6$0^{\circ}C$. We tan reduce eddy current loss as a primary loss of high frequency by adding a small amount of V$_2$O$_{5}$와 CaCo$_3$. This reduces power loss in the power transformersormers

• Wind and Structures
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• v.36 no.4
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• pp.263-275
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• 2023

As a new kind of construction facility for high rise buildings, the integral steel platform scaffold system (ISPS) consisting of the steel skeleton and suspended scaffold faces high wind during the construction procedure. The lattice structure type and existence of core tubes both make it difficult to estimate the wind load and calculate the wind-induced responses. In this study, an aeroelastic model with a geometry scale ratio of 1:25 based on the ISPS for Shanghai Tower, with the representative square profile, is manufactured and then tested in a wind tunnel. The first mode of the prototype ISPS is a torsional one with a frequency of only 0.68 Hz, and the model survives under extreme wind speed up to 50 m/s. The static wind load and wind vibration factors are derived based on the test result and supplementary finite element analysis, offering a reference for the following ISPS design. The spacer at the bottom of the suspended scaffold is suggested to be long enough to touch the core tube in the initial status to prevent the collision. Besides, aerodynamic wind loads and cross-wind loads are suggested to be included in the structural design of the ISPS.

• Journal of the Korean Magnetics Society
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• v.9 no.5
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• pp.234-238
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• 1999

Lithium ferrites are prominent in the element of microwave frequency communication core and high frequency memory core because of their low coercivity and the high squareness ratio. This paper reports primarily the development of lithium ferrites with the low coercivity and high squareness ratio. The materials with $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (x = 0,0.01, 0.02, 0.03) have been prepared to investigate the physical properties. The addition of ZnO gave raised maximum induction $(B_m)$ and decreased coercive force $(H_c)$, but the squareness ratio $(R\;=\;B_m/B_r)$ was decreased. The specimen of squareness ratio R=0.82, coercive force $H_c=\;1.80\;Oe$ was obtained for $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (X=0) sintered at 105$0^{\circ}C$. Also the sample of squareness ratio R = 0.75, coercive force $H_c=\;1.70\;Oe$ for $Li_{0.48-0.5x}Bi_{0.02}Ni_{0.04}Zn_xFe_{2.46-0.5x}O_4$ (X = 0) sintered at 110$0^{\circ}C$ was measured. The Tc was obtained 463$^{\circ}C$ and the Br of environmental temperature variation was stable.