• Journal of Power Electronics
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• v.11 no.6
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• pp.870-879
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• 2011

Regulated peak power tracking (RPPT) systems such as the series structure and the series-parallel structures are commonly used in satellite space power systems. However, these structures process the solar array power or the battery power to the load through two cascaded regulators during one orbit cycle, which reduces the energy transfer efficiency. Also the battery charging time is increased due to placement of converter between the battery and the solar array. In this paper a parallel structure has been proposed which can improve the energy transfer efficiency and the battery charging time for satellite space power RPPT systems. An analogue controller is used to control all of the required functions, such as load voltage regulation and solar array stabilization with maximum power point tracking (MPPT). In order to compare the system efficiency and the battery charging efficiency of the proposed structure with those of a series (conventional) structure and a simplified series-parallel structure, simulations are performed and the results are analyzed using a loss analysis model. The proposed structure charges the battery more quickly when compared to the other two structures. Also the efficiency of the proposed structure has been improved under different modes of solar array operation when compared with the other two structures. To verify the system, experiments are carried out under different modes of solar array operation, including PPT charge, battery discharge, and eclipse and trickle charge.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.3
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• pp.193-201
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• 1996

The space power system for communication satellite which employs the direct energy transfer (DET) method consists of solar array, battry, shunt regulator, charger/discharger and power control unit (PCU). In this paper, the development of the DET power system charger/discharger unit and a microprocessor based PCU is developed for simplicity and flexiblity in the modificatin of control algorithm. A 28V bus voltage, 400W power rting power simulator is built and tested to verify the operation of the simulator at each mode and the stability of mode transition is analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.59-66
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• 2014

In the case of a propeller-driven aircraft, power-on effect generated by the propeller has a strong influence on the performance and the stability of an aircraft directly and indirectly. A numerical study on the power-on effect has been performed using the CFD based on the multiple reference frame and sliding mesh model. The power-on effect increases the overall lift and the maximum lift of the aircraft. In addition to lift increment, power-on effect delays the stall of the aircraft. On the other hand, the power-on effect increases the drag significantly and consequently decreases the lift-to-drag ratio of the aircraft. Furthermore, the power-on effect decreases the nose-down pitching moment and consequently decreases the longitudinal static stability of the aircraft. It is expected that the analysis results presented and discussed in this report will be used as an important material for analyzing the aircraft performance and stability and will contribute the development of the propeller-driven aircraft with the pusher propeller.

• Journal of The Korean Astronomical Society
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• v.55 no.5
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• pp.173-194
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• 2022

We complete the survey for finite-source/point-lens (FSPL) giant-source events in 2016-2019 KMTNet microlensing data. The 30 FSPL events show a clear gap in Einstein radius, 9 𝜇as < 𝜃_E < 26 𝜇as, which is consistent with the gap in Einstein timescales near t_E ~ 0.5 days found by Mróz et al. (2017) in an independent sample of point-source/point-lens (PSPL) events. We demonstrate that the two surveys are consistent. We estimate that the 4 events below this gap are due to a power-law distribution of free-floating planet candidates (FFPs) dN_FFP/d log M = (0.4 ± 0.2) (M/38 M_⊕)^-p/star, with 0.9 ≲ p ≲ 1.2. There are substantially more FFPs than known bound planets, implying that the bound planet power-law index 𝛾 = 0.6 is likely shaped by the ejection process at least as much as by formation. The mass density per decade of FFPs in the Solar neighborhood is of the same order as that of 'Oumuamua-like objects. In particular, if we assume that 'Oumuamua is part of the same process that ejected the FFPs to very wide or unbound orbits, the power-law index is p = 0.89 ± 0.06. If the Solar System's endowment of Neptune-mass objects in Neptune-like orbits is typical, which is consistent with the results of Poleski et al. (2021), then these could account for a substantial fraction of the FFPs in the Neptune-mass range.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.3
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• pp.245-250
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• 2000

This study was carried out to investigate blowing performance for blowing type in space heater. This paper present that power requirement, static pressure, total pressure and static pressure efficiency were increased in proportion to air flow rate. And in the Korean space heater, side ward blowing type was effected than downward blowing type.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.69-74
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• 2012

According to convert from analogue TV signal to Digital TV signal on 31 December 2012, research on utilization of TV white space (TVWS) has been being actively proceed. It is expected that various low power devices use the TVWS, so interference between DTV relay system and low power devices using in TVWS can be occurred. Therefore, in this paper, we analyzed the interference between DTV relay system and low power devices. So, we calculated a minimum coupling loss (MCL) and compare the resulting value with a path loss for determining whether there exists a potential interference or not. The minimum separation distance is determined when the path loss is larger than the MCL. In the simulation results, we setup the victim and interferer system as DTV relay system and low power devices, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.92.1-92.1
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• 2013

In this study, we examined chromospheric oscillation signatures in two solar active regions, a limb active region and a sunspot with a light bridge, observed by the Fast Imaging Solar Spectrograph (FISS) of the 1.6m New Solar Telescope (NST) at Big Bear Solar Observatory. The FISS is a slit spectrograph with a fast imaging capability and can observe the solar chromosphere in $H{\alpha}$ and Ca II $8542{\AA}$ bands simultaneously with high spectral resolutions. After dark and flat correction, we compensated for image rotation at the Coude focus and made image alignment. We estimated Doppler shifts over active regions using the bisector method and investigated the temporal and spatial fluctuations of Doppler shifts for some selected cases. And we obtain the power map by using the Lomb-Scargle periodogram technique to examine the oscillation power at different features. Finally, we will discuss our results and implications.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.6
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• pp.525-537
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• 2001

In this paper a new space vector RPPWM(Random Position PWM) is proposed. In the propsed RPPWM each of three phase pulses is located randomly in each switching interval. Based on the Space vector modulation technique the duty ratio of the pulses is calculated Along with the randomization of the PWM pulses. we can obtain the effects of spread spectra of votlage, current as in the case of randomly changed switching frequency, To verify the validity of the proposed RPPWM simulation study was tried using Matlab/Simulink The main model described in Simulink block diagrams includes the space vector modulation block pulse position randomization block inverter block 3 phase induction motor block and so on By the simulation study, the harmonics of the output voltage and the current of inverter are predicted in different PWM methods- SVPWM, LLPWM proposed RPPWM.

• Journal of Power Electronics
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• v.10 no.5
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• pp.468-476
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• 2010

This paper proposes and develops a new direct voltage control (DVC) approach. This method is designed to be applied in various applications for AC drives fed with a three-phase voltage source inverter (VSI) working with a constant switching time interval as in the standard direct torque control (DTC) scheme. Based on a very strong min(max) criterion dedicated to selecting the inverter voltage vector, the developed DVC scheme allows the generation of accurate voltage forms of waves. The DVC algorithm is implemented on a dSPACE DS1104 controller board and then compared with the space vector pulse width modulation technique (SVPWM) in an open loop AC drive circuit. To demonstrate the efficiency of the developed algorithm in real time and in closed loop AC drive applications, a scalar control scheme for induction motors is successfully implemented and experimentally studied. Practical results prove the excellent performance of the proposed control approach.

• Korean Institute of Interior Design Journal
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• no.14
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• pp.10-18
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• 1998

This study aims to make clear visual quality of organic form and structural order that is immanent in nature about a form as formative principles of architectural space design the significanced of this study is to prove the application possibility in to functional form architectural space design. All organic forms in nature has a unique shape and pattern in structure to be self-controled and good in order. Such an order in nature comes from regular construction and ratio principles which has aesthetical order by mathmetics. The specialty of beauty in nature can be revealed not only visual form but also the ratio balance and rhythm of structural principles. As we examine the aesthetic source embodied some object can be developed in to basic principles. Furthermore through this study we can find out that the form construction theory in nature forms share the quality attribute with geometrical form to be shown in architectural space design. Natural forms are ultimate visual expression of power that effects on the architectural space design. The rule of power in nature as nature formal characteristics have a direct influence and can be also applied to architectural construction. Therefore I expect that this study will be linked and continued to another structural view.