• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.3
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• pp.492-498
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• 2010

Since it is almost impossible to train the dispatchers with real power system, the dispatcher training simulator(DTS) is used for the training. Among various components of the DTS, the power system model(PSM) emulates the dynamic behavior of the power system to calculate the frequency and voltage. The frequency is calculated from various parameters such as mechanical power of power plants, load, inertia, and the damping of the power system. In the PSM, the power plants are modeled as differential equations, so the mechanical power of the power plants are calculated by the numerical methods. Conventionally, the fixed step-size algorithm has been used in the PSM, however it has some drawbacks. This paper develops the prototype PSM using the Matlab, and analyzes the problems of the fixed step-size algorithm by comparing the results with those of PSCAD simulation. In order to overcome the limitations, this paper proposes a modified frequency calculation method using the adaptive step-size algorithm. From the simulation using the proposed method, it is verified that the accuracy of frequency calculation increases substantially while the simulation time is not greatly increased.

• Journal of Power Electronics
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• v.3 no.2
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• pp.139-144
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• 2003

In this paper, 11 and 13 layered step-down piezoelectric transformers were fabricated and their electrical characteristics have been analyzed for AC-adapter. When the voltage is applied to the driving piezoelectric vibrator polarized in the longitudinal direction, the output voltage is generated at the generating piezoelectric vibrator polarized in the thickness direction due to the piezoelectric effects. From the piezoelectric direct and converse effects, symbolic expressions between the electric inputs and outputs of the step-down piezoelectric transformer are derived with an equivalent circuit model. With those expressions, load and frequency characteristics are discussed through the simulations. Output voltage and current from a 11-layered and a 13-layered piezoelectric transformers were measured under the different load and frequency conditions. First we measured resonant frequency from impedance curve and got equivalent impedance value of the piezoelectric transformer from admittance plot. It was shown from experiments that output voltage increase s and resonant frequency changes according to the various resistor loads. Output current decreases inversely proportional to the change of loads. Moreover, the measured output voltage and current are well matched with the simulated results obtained from the proposed equivalent circuit model. Furthermore, a new step-down piezoelectric transformer has been suggested to Increase the output power based on a simulation result having a driving piezoelectric vibrator polarized thickness direction.

• IE interfaces
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• v.18 no.3
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• pp.333-342
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• 2005

In this paper, we propose an efficient forecasting methodology of the mid and long-term frequency demand in Korea. The methodology consists of the following three steps: classification of basic service group, calculation of effective traffic, and frequency forecasting. Based on the previous studies, we classify the services into wide area mobile, short range radio, fixed wireless access and digital video broadcasting in the step of the classification of basic service group. For the calculation of effective traffic, we use the measures of erlang and bps. The step of the calculation of effective traffic classifies the user and basic application, and evaluates the effective traffic. Finally, in the step of frequency forecasting, different methodology will be proposed for each service group and its applications are presented.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.345-352
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• 2017

In this paper, a non-dissipative snubber for reducing the switching losses in the step down converter is proposed. The conventional step down converter, e.g., buck converter, suffers from serious switching losses and consequentially heat generation because of its hard switching. Thus, it is unsuitable for high switching frequency operation. Reduction of the reactive components' size, such as an output inductor and capacitor, is difficult. The proposed snubber can slow down the increasing current slopes and switch voltage at turn-on and turn-off transients, thereby significantly reducing the switching loses. Additionally, the slowly increasing current during switch turn-on transition, can effectively solve the output rectifier diode reverse recovery problem. Therefore, the proposed non-dissipative snubber not only leads to the efficiency of converter operation at high switching frequency but also reduces the reactive components size in proportion to the switching frequency. To confirm the validity of the proposed circuit, theoretical analysis and experimental results from a 150 W, 1 MHz prototype are presented.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.2
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• pp.157-163
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• 2014

This paper proposes a two-stage step-down buck and a tapped-inductor boost cascaded converter for high efficiency photovoltaic micro-inverter applications. The proposed inverter is a new structure to inject a rectified sinusoidal current into a low-frequency switching inverter for single-phase grid with unity power factor. To build a rectified-waveform of the output current. the converter employs both of a high efficiency step-up and a step-down converter in cascade. In step-down mode, tapped inductor(TI) boost converter stops and the buck converter operates alone. In boost mode, the TI converter operates with the halt of buck operation. The converter provides a rectified current to low frequency inverter, then the inverter converts the current into a unity power-factor sinusoidal waveform. By applying a TI, the converter can decrease the turn-on ratios of the main switch in TI boost converter even with an extreme step-up operation. The performance validation of the proposed design is confirmed by an experimental results of a 120W hardware prototype.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.4
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• pp.97-103
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• 2011

The most important object of grounding systems is to protect human being from electric shock. Touch and step voltages are measured to evaluate the performances of grounding systems. Dangerous voltages have been largely studied by the power frequency fault currents, on the other hand, the ground current containing the high frequency components and surge currents haven't been considered. Many attempts about the grounding impedances reported in these days show that the performance of the grounding systems in high frequency range is very different with the ground resistance. It is necessary to analyze the dangerous voltages formed by the ground currents containing high frequency components. In this paper, the ground surface potential rises near the vertical and horizontal grounding electrodes are measured at the frequency of 100[Hz], 30[kHz], and 100[kHz]. Dangerous voltages are investigated with the frequency-dependent grounding impedance. As a result, the ground surface potential rise is increased as the grounding impedance increases. Touch and step voltages near the grounding electrode whose impedance increases with the frequency are sharply raised.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.234-237
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• 2008

This paper deals with a new single-phase Z-source matrix converter (SZMC) topology. Unlike other conventional configurations, the proposed SZMC is not only a step-up frequency converter but also a step-down frequency converter and a voltage boost capability. Thus, the proposed SZMC is also called a frequency step-up/down and voltage step-up converter. A safe-commutation strategy is used in SZMC as free-wheeling operation to eliminate voltage spikes on switches. The operating principles and experimental results of the proposed SZMC are presented.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.671-674
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• 2004

This paper presents design and analysis of multi-layered ring-dot type piezoelectric transformer. These transformers are useful for step up and step down. The transformers consist of disk type multi-layered piezoelectric ceramic plates. The finite element method(FEM) was used for analysis transformer. Vibration mode, electric field and equivalent elastic strain of piezoelectric transformer were simulated by changing frequency. As results, the strain was distributed in isolation part entirely. We can get the operated in step up transformer when the inner side electrode using by input parts. Also we can get the step down transformers using by input Part as outer side electrode. The step up ratio and step down ratio was increased by decreasing inner side electrode. The resonance frequency was increased by increasing inner side electrode when the transformer was operated in step down transformer. But the step up one was decreased. From these results, we can expect to multi-layered ring-dot type piezo transformers as step up and step down transformers.

• Journal of Industrial Technology
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• v.16
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• pp.123-129
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• 1996

A method of calculating the natural frequency corresponding to the first mode of vibration of beams and tower structures with irregular cross-sections and with arbitrary boundary conditions was developed and reported by D. H. Kim in 1974. In order to obtain the natural frequency by the presented method, the first step to take is to obtain the deflection influence surfaces. In design and analysis of any structure, the first step to be taken is to obtain this deflection influence surfaces. Any method can be used for this purpose. Then using this surfaces, deflections, slopes, moments, shears, and natural frequencies can be obtained by differentiating either the continuous function or discrete function defined at certain points. The merit of the presented method is that the natural frequency can be obtained by the deflection influence surfaces obtaining which is the first step in structural analysis.

• Journal of information and communication convergence engineering
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• v.8 no.2
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• pp.159-162
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• 2010

This paper presents a new Kurtosis driven Variable Step-Size Normalized Least Mean Square (KVSSN-LMS) algorithm to prevent repeater from oscillation due to feedback signal of radio frequency (RF) repeater. To get better Mean Square Error (MSE) performance, step-size is adjusted using the kurtosis. The proposed algorithm shows the better performance of steady state MSE. The proposed algorithm shows a better ERLE performance than that of KVSS-LMS, VSS-NLMS, NLMS algorithms.