• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.5
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• pp.67-71
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• 2010

This paper proposes new dual-band impedance transformers based on the L-section circuit topology. The proposed circuits consist of a transmission line section with a stub line either at the source or at the load end. The dual-band operating conditions are analyzed in detail and simple design equations are derived in terms of the line lengths and impedances for the different circuit topologies and load conditions. The dual-band operation is confirmed through the design, fabrication and measurement in microstrip circuits based on the proposed method.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1348-1349
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• 2008

Grounding impedance depends on the frequency of current flowing into a grounding system. Especially, the lightning gives a broad frequency spectrum from low frequency up to 1 MHz. So the grounding impedance related to high frequency current like lightning should be measured with high frequency source. In this paper, we described the grounding impedances of deeply-driven ground rods of 10 $\sim$ 48 m long with respect to the frequency of injected currents. For the experiments, we used the wideband power amplifier which can produce sinusoidal voltages with the frequency ranges of DC $\sim$ 250 MHz. As a result, the longer the ground rod is, the lower the ground resistance is. However the grounding impedance of deeply-driven ground rod in the range of higher frequency is significantly increased. As a consequence, it is important to evaluate the high frequency performance of grounding systems for lightning protection.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.70-73
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• 2008

Grounding impedance depends on the frequency of current flowing into a grounding system. Especially, the lightning gives a broad frequency spectrum from low frequency up to 1 MHz. So the grounding impedance related to high frequency current like lightning should be measured with high frequency source. In this paper, we described the grounding impedances of deeply-driven ground rods of 10 ${\sim}$ 48 m long with respect to the frequency of injected currents and the feed point. For the experiments, we used the wideband power amplifier which can produce sinusoidal voltages with the frequency ranges of DC ${\sim}$ 250 MHz. As a result, the longer the ground rod is, the lower the ground resistance is. However the grounding impedance of deeply-driven ground rod in the range of higher frequency is significantly increased. As a consequence, it is important to evaluate the high frequency performance of grounding systems for lightning protection.

• 전기의세계
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• v.21 no.1
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• pp.7-12
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• 1972

General steady state equivalent circuits are derived for the family of single phase motor having two windings with non-quadrature. First, the fundamental voltage equations of motor are derived by Faraday-Krichhoff's low in the fiew of the flux distribution in the modified motor with Kron primitive machine. Those equations are arranged in to f-b equations by transformation matrix. To using the above equations for circuit; 1) The concept of current-source was much help to sove the realtions between matrix impedance equation and circuit analysis 2) The simplification of the circuit to the mutual impedance matrix elements is easy to considerations of motor characteristics in the case of inserted external auxiliary winding impedance. Finally, this equivalent circuit showing as a single phase induction motor with quadrature winding is described by each conditions.

• Proceedings of the IEEK Conference
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• 2001.06e
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• pp.241-244
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• 2001

This paper proposes a nonlinear impedance circuit composed by diodes and inductors or capacitors. This circuit needs no control circuits and switches, and the impedance value is changed by the polarity of current or voltage, This paper presents one of these applications to improve the input current of capacitor input diode rectifiers. The rectifier using the nonlinear impedance circuit id constructed with four diodes and four capacitors in addition to the conventional rectifiers, that is it has eight diodes and five capacitors, including a DC link capacitor. It makes harmonic components of the input current reduce and the power factor improve. A circuit design method is shown by experimentation and confirmed simulation. It explained that compared conventional pulse-width modulated (PWM)inverter with half pulse-width modulated (HPWM) inverter. Proposed HPWM inverter eliminated dead-time by lowering switching loss and holding over-shooting.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.585-592
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• 2003

The parallel operation system of UPS is used to increase reliability of power source at critical load. But parallel UPS system has a few defects, impedance is different from each other and circulating current occurs between UPSs, due to line impedance and parameter variation, though controlled by the same synchronization signal. According to such characteristic of parallel UPS, balanced load-sharing control is the most important technique in parallel UPS operation. In this paper, a novel power deviation compensation algorithm is proposed. it is composed of voltage controller to compensate power deviation that be calculated by using active and reactive current deviation between Inverters on synchronous d-q reference frame.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.1-7
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• 2014

This paper proposes a current harmonic compensation method for the grid-connected inverter, especially caused by the grid impedance. Grid impedance causes low order harmonics in the grid current and deteriorates power quality. This paper analyzes the negative impact of the grid impedance, and proposes an active feedforward compensation method. Proposing method verified through simulation and experiment with 3-phase 1.5kW voltage source inverter prototype.

• Journal of IKEEE
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• v.24 no.4
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• pp.982-990
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• 2020

Groundwater is essential source of the freshwater. Groundwater is stored in the body of the rocks or sediments, called aquifer. Finding an aquifer is a very important part of the geophysical survey. The best method to find the aquifer is to make a borehole. Single borehole is not a suitable method if the aquifer is not located in the borehole drilled area. To overcome this problem, a cross borehole method is used. Using a cross borehole method, we can estimate aquifer location more precisely. Electrical impedance tomography is use to estimate the aquifer location inside the subsurface using the cross borehole method. Electrodes are placed inside each boreholes and area between these boreholes are analysed. An aquifer is a non-uniform structure with complex shape which can represented by the truncated Fourier series. Deep neural network is evaluated as an inverse problem solver for estimating the aquifer boundary coefficients.

• Journal of Power Electronics
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• v.18 no.1
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• pp.234-250
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• 2018

This paper presents a new load sharing control for use between paralleled three-phase inverters in an islanded microgrid based on the online line impedance estimation by the use of a Kalman filter. In this study, the mismatch of power sharing when the line impedance changes due to temperature, frequency, significant differences in line parameters and the requirements of the Plug-and-Play mode for inverters connected to a microgrid has been solved. In addition, this paper also presents a new droop control method working with the line impedance that is different from the traditional droop algorithm when the line impedance is assumed to be pure resistance or pure inductance. In this paper, the line impedance estimation for parallel inverters uses the minimum square method combined with a Kalman filter. In addition, the secondary control loops are designed to restore the voltage amplitude and frequency of a microgrid by using a combined nominal value SOGI-PLL with a generalized integral block and phase lock loop to monitor the exact voltage magnitude and frequency phase at the PCC. A control model has been simulated in Matlab/Simulink with three voltage source inverters connected in parallel for different ratios of power sharing. The simulation results demonstrate the accuracy of the proposed control method.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.165-169
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• 2004

In Magnetic Resonance Electrical Impedance Tomography (MREIT), we inject current through electrodes placed on the surface of a subject and measure the induced magnetic flux density distribution using an MRI scanner. This requires a constant current source whose output pulses are synchronized with MR pulse sequences. In this paper, we present a design and performance analysis of a current source used in a 3.0T MREIT system. The developed current source was tested using a saline phantom. We found that its performance is satisfactory for the current MREIT system. We suggest future improvements for better SNR(signal-to-noise ratio).