• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.5
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• pp.321-327
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• 2018

DC microgrid system composed of multiple converters has a tendency to make the system unstable due to the interaction of converters. To solve this problem, in this paper, the interaction between cascaded converters with LC input filter is analyzed with impedance modeling using g-parameter. The input impedance and the output impedance of the system can be obtained through this technique. The stability of the system can be determined by applying Middlebrook's stability criterion to the impedance. Virtual impedance is added to the controller to enhance stability. The validity of the analysis is verified by the result of several simulations and experiments.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.475-478
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• 2006

In electrical impedance tomography (EIT) an array of electrodes is attached on the boundary of an object and small alternating currents are injected through these electrodes, and then the resulting voltages are measured. An estimation for the cross-sectional resistivity distribution in the object is obtained by using these current and voltage data in a nondestructive manner. In this paper, the electrical impedance imaging of two-phase flows undergoing rapid transient is considered with a special emphasis on the effect of the current pattern on the image reconstruction. The trigonometric current pattern, which is commonly used in the conventional static electrical impedance imaging, shows poor performance in case of the dynamic imaging considered in this work. Extensive numerical experiments are conducted with various kinds of current patterns and their effects on the image reconstruction performance are examined.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.2
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• pp.229-234
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• 2008

An AC-DC transfer standard(TS) is used for the AC voltage standard in the range of 2 mV to 1000 V below 1 MHz. Micro-potentiometer(${\mu}Pot$) is used to evaluate the ac-dc transfer difference(ADD) of the TS below 200 mV range. The ADD of the TS were changed by the loading effect caused from the input impedance change of the TS depend on frequency. An input impedance evaluation technique of the TS using ${\mu}Pot$ has been developed.

• Korean Journal of Optics and Photonics
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• v.20 no.2
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• pp.65-70
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• 2009

In this paper, a THz Yagi-Uda antenna with high input impedance is designed. By placing the antenna on a thin substrate, end-fire radiation patterns with high antenna impedance can be obtained even when the substrate has high relative dielectric constant. The proposed Yagi-Uda antenna has high input resistance of approximately $4,400{\Omega}$ at the resonance frequency which is obtained by using a U-shaped dipole as a driver element. It is expected that the Yagi-Uda antenna on a thin substrate can achieve much higher terahertz output power than the conventional THz antennas.

• Journal of Power Electronics
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• v.9 no.3
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• pp.447-455
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• 2009

The power supply systems, which require low-voltage / high-current output has been changing from the conventional centralized power system to a distributed power system. The distributed power system consists of a bus converter and POL. The most important factor is the system stability in bus architecture design. The overlap between the output impedance of a bus converter input impedance of POL causes system instability and has been an actual problem. By increasing the bus capacitor, the system stability can be easily improved. However, due to limited space on the system board, the increasing of bus capacitors is impractical. An urgent solution of this issue is strongly desired. This paper presents the output impedance design for on-board distributed power system by means of three control schemes of a bus converter. The output impedance peak of the bus converter and the input impedance of the POL are analyzed and then conformed experimentally for stability criterion. Furthermore, the design process of each control schemes for system stability is proposed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.5
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• pp.612-619
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• 2013

This paper proposes an early diagnosis technique for the stator-turn fault (STF) in an interior permanent magnet (IPM)-type brushless DC (BLDC) motor using the impedance parameter. We have analyzed the varying characteristics owing to the STF through various experiments and the finite element method (FEM). As a result, we have presented a simple method for fault detection. This technique can be applied without requiring a fast Fourier transform (FFT) and the calculation of the negative-sequence impedance. The fault detection system works on the basis of the comparison the measured impedance with the database impedance. The variations in the characteristics owing to the STF as well as the proposed technique have been verified through the simulation and experiment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.7
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• pp.89-94
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• 2013

This paper presents a method of simulating the protection effects of surge protective devices(SPDs) depending on the protective distance and types of input impedance of load to be protected. In order to analyze the protective performances of voltage-limiting type SPDs associated with the reflection and oscillation phenomena, the terminal voltage across load being protected and the residual voltage of SPDs were simulated by using EMTP model as functions of the protective distance and types of input impedance of loads. As a consequence, SPDs should be installed by taking into account the protective distance and input impedance of loads to achieve reliable protection of electrical and electronic equipment from lightning and switching surges. It is expected that the simulation method proposed in this paper could be practically used in design for installing SPDs in low-voltage distribution systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.67-78
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• 2005

In this paper, impedance characteristics of overhead medium-voltage (MV) power line for power line communication (PLC) is analyzed. For analysis, a two-port equivalent network model of MV power lines is derived. By applying the equivalent model and basic transmission line theory, input impedance at the signal induction part is calculated. And also calculated input impedance of power line itself that the medium voltage coupler and coaxial cable effect are removed. For verification, impedance of power lines is measured at a test field for an MV PLC. The results show that impedance of MV power line itself is between $200\;{\Omega}\;and\;300\;{\Omega}$ and converges to a half of their characteristic impedance with increasing frequency. And also measured data is very similar to calculated data.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.7
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• pp.537-548
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• 2014

In this paper, horn loudspeaker modeling was suggested, investigated and verified through comparison of test results and simulation ones based on input electrical impedance curves and acoustic sensitivity ones. First, Thiele Small parameters of horn driver were identified by using pseudo loudspeaker model concept and verified in case of both closed and open horndriver. Second, cone-shaped horn models were investigated and compared with input acoustic impedance curves for real horn(cone angle $6.6^{\circ}$) and short horn(cone angle $27.9^{\circ}$). It showed that Leach model for cone horn was well described to test results, which were electrical impedance and acoustic sensitivity, compared to Lemaitre one. To represent horn system model good approximation in wide frequency range, mass correction filter and lowpass filter were adopted and consequently showed good fitted to test results.

• Journal of Electrical Engineering and Technology
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• v.2 no.1
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• pp.29-34
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• 2007

The input and output impedances in a low voltage distribution system is one of the most important matters for power line communication because from the viewpoint of communication, the attenuation characteristic of the high frequency signals is greatly caused by impedance mismatch during sending and receiving. The frequency range is from 1MHz to 30MHz. Therefore, this paper investigates the input and output impedances in order to understand the characteristic of high frequency signals in the low voltage distribution system between a pole transformer and an end user. For power line communication, the model of Korea's low voltage distribution system is proposed in a residential area and then the low voltage distribution system is set up in a laboratory. In the low voltage distribution system, S parameters are measured by using a network analyzer. Finally, input and output impedances are calculated using S parameters.