• ETRI Journal
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• v.41 no.1
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• pp.124-132
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• 2019

The energy balance (EB) model of a primary side regulation (PSR) fly-back converter in the discontinuous conduction mode (DCM) is discussed in this paper. Based on this EB model, the stability of a PSR fly-back converter in the pulse skipping mode (PSM) is analyzed, and a self-adapting modulation factor control strategy is proposed. Theoretical analysis and simulation results show that by saving an optocoupler and correlative circuits, which are necessary in traditional PSM fly-back converters, the modulation factor tolerance controlled by this method is 1.26% on average, corresponding to the ideal value. Compared with traditional fly-back PSM controllers, the power saved in the sampler/comparator modules is 87% on average for a load range of $1{\Omega}$ to $1k{\Omega}$.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.6
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• pp.441-448
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• 2007

To enhance the competitive edge of the material cost, IP(Integrated Power) Board form of inverter circuit is widely used in large area LCD TV(Greater than or equal to 40 in.). This scheme is Two Stage System and one inverter drives multi-lamp in a parallel circuit. This paper analyzes the conventional IP Board inverter controlled with Pulse Width Modulation (PWM), and its problems such as serious hard switching and excessive circulating energy can be solved by a proposed Pulse Count Modulation (PCM) scheme. To confirm the validity and superiority of the proposed system, theoretical analysis and experimental results are presented.

• Journal of Power Electronics
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• v.16 no.1
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• pp.153-162
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• 2016

Given their structural arrangement, photovoltaic (PV) modules exhibit parasitic capacitance, which creates a path for high-frequency current during zero-state switching of the converter in transformerless systems. This current has to be limited to ensure safety and electromagnetic compatibility. Many solutions that can minimize or completely avoid this phenomenon, are available. However, most of these solutions are patented because they rely on specific and often complex converter topologies. This study aims to solve this problem by introducing a solution based on a classic converter topology with an appropriate modulation technique and passive filtering. A 5.5 kW single-phase residential PV system that consists of DC-DC boost stage and DC-AC H-bridge converter is considered. Control schemes for both converter stages are presented. An overview of existing modulation techniques for H-bridge converter is provided, and a modification of hybrid modulation is proposed. A system prototype is built for the experimental verification. As shown in the study, with simple filtering and proper selection of switching states, achieving low leakage current level is possible while maintaining high converter efficiency and required energy quality.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1637-1643
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• 2018

To reduce the laser pulse shape distortion accompanying the amplification process and achieve an intended output pulse shape in the Nd:YAG amplifier chain, we propose a frequency-modulated pulse-amplification method. Assuming carrier-frequency-modulated seed pulses, we numerically simulate the pulse amplification in an Nd:YAG amplifier chain where severe distortion occurs. For the calculation, we develop a modified Frantz-Nodvik equation, which enables two inputs with different carrier frequencies. The simulation results indicate that the temporal contrast of the seed pulse needed to obtain a flat output pulse shape is reduced by 16 - 25 dB when frequency modulation is applied.

• Journal of Power Electronics
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• v.19 no.2
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• pp.560-568
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• 2019

This paper studies the inherent relationship between currents and zero-sequence components. Then a precise algorithm is proposed to calculate the injected zero-sequence component to control the DC-Link neutral-point voltage balance, which can result in a more efficient and flexible neutral point voltage balance with a desirable performance. In addition, it is shown that carried-based PWM with the calculated zero-sequence component scheme can be equivalent to space-vector pulse-width modulation (SVPWM). Based on the proposed method, the optimal zero-sequence component of the feasible modulation indices is analyzed. In addition, the unbalanced load limitation of the DC-Link neutral-point voltage balance control is also revealed. Simulation and experimental results are shown to verify the validity and practicality of the proposed algorithm.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.20-20
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• 1999

• Progress in Medical Physics
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• v.27 no.1
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• pp.31-36
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• 2016

The paper discusses radiation dose of dual energy CT on which copper modulation layer, is mounted in order to improve diagnostic performance of the dual energy CT. The radiation dose is estimated using MCNPX and its results are compared with that of the conventional dual energy CT system. CT X-ray spectra of 80 and 120 kVp, which are usually used for thorax, abdominal, head, and neck CT scans, were generated by the SPEC78 code and were used for the source specification 'SDEF' card for MCNPX dose modeling. The copper modulation layer was located 20 cm away from a source covering half of the X-ray window. The radiation dose was measured as changing its thickness from 0.5 to 2.0 mm at intervals of 0.5 mm. Since the MCNPX tally provides only normalized values to a single particle, the dose conversion coefficients of F6 tally for the modulation layer-based dual energy CBCT should be calculated for matching the modeling results into the actual dose. The dose conversion coefficient is $7.2*10^4cGy/output$ that is obtained from dose calibration curve between F6 tally and experimental results in which GAFCHORMIC EBT3 films were exposed by an already known source. Consequently, the dose of the modulation layer-based dual energy cone beam CT is 33~40% less than that of the single energy CT system. On the basis of the results, it is considered that scattered dose produced by the copper modulation layer is very small. It shows that the modulation layer-based dual energy CBCT system can effectively reduce radiation dose, which is the major disadvantage of established dual energy CT.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9A
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• pp.835-843
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• 2010

Energy spreading transform (EST) based equalization is a very effective technique to remove inter symbol interference (ISI) in frequency selective channel. EST based system uses cyclic prefix (CP) similar to orthogonal frequency division multiplexing (OFDM) system. Since CP is a redundancy, it degrades the data transmission rate. RISIC is an algorithm that removes an inter block interference (IBI) caused by insufficient CP length and reconstructs CP. In this paper, we propose a system that combines the existing EST system with quadrature phase shift keying (QPSK) modulation and RISIC algorithm to enhance the efficiency of the transmission. Also we extend the proposed system to 16 quadrature amplitude modulation (QAM) modulation. The proposed system is shown to performance close to matched filter bound (MFB) even with insufficient CP.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.1-5
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• 2004

Tunable diode laser absorption spectroscopy was performed for analysis of the H$_2$$^{18}$ O/H$_2$$^{16}$ O isotope ratio of a water sample which was enriched by the membrane distillation method. In order to improve the signal-to-noise ratio, the wavelength modulation spectroscopic method was used with a lock-in amplifier. The fringe noise could be suppressed by using the FFT (Fast Fourier Transform) lowpass filter and the optimization of the modulation depth of the laser frequency. The maximum deviation of $\delta$-value was measured to be$\pm$4$\textperthousand$.

• ETRI Journal
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• v.38 no.4
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• pp.735-745
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• 2016

The Paris agreement at the 21st Conference of the Parties (COP21) emphasizes the reduction of greenhouse gas emissions and increase in energy consumption in all areas. Thus, an important aspect is energy saving in buildings where the lighting is a major component of the electrical energy consumption. This paper proposes a building energy management system employing visible light communication (VLC) based on LED lighting. The proposed management system has key characteristics including personalization and localization by utilizing such VLC advantages as secure communication through light and location-information transmission. Considering the efficient implementation of an energy-consumption adjustment using LED luminaires, this paper adopts variable pulse position modulation (VPPM) as a VLC modulation scheme with simple controllability of the dimming level that is capable of providing a full dimming range. This paper analyzes the VPPM performances according to variable dimming for several schemes, and proposes a VPPM demodulation architecture based on dimming-factor acquisition, which can obtain an improved performance compared to a 2PPM-based scheme. In addition, the effect of a dimming-factor acquisition error is analyzed, and a frame format for minimizing this error effect is proposed.