• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.38.2-38.2
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• 2016

The mapping of dark matter clustering from real to redshift spaces introduces the anisotropic property to the measured density power spectrum in redshift space, known as the Redshift Space Distortion (hereafter RSD) effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to the indefinite cross correlations between the density and velocity fields, and the Finger-of-God (hereafter FoG) effect due to the randomness of the peculiar velocity field. Furthermore, the rigorous test of this mapping formula is contaminated by the unknown non-linearity of the density and velocity fields, including their auto- and cross-correlations, for calculating which our theoretical calculation breaks down beyond some scales. Whilst the full higher order polynomials remains unknown, the other systematics can be controlled consistently within the same order truncation in the expansion of the mapping formula, as shown in this paper. The systematic due to the unknown non-linear density and velocity fields is removed by separately measuring all terms in the expansion using simulations. The uncertainty caused by the velocity randomness is controlled by splitting the FoG term into two pieces, 1) the non-local FoG term being independent of the separation vector between two different points, and 2) the local FoG term appearing as an indefinite polynomials which is expanded in the same order as all other perturbative polynomials. Using 100 realizations of simulations, we find that the best fitted non-local FoG function is Gaussian, with only one scale-independent free parameter, and that our new mapping formulation accurately reproduces the observed power spectrum in redshift space at the smallest scales by far, up to k ~ 0.3 h/Mpc, considering the resolution of future experiments.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.1
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• pp.18-26
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• 2017

This paper proposes the model predictive control with space vector modulation (SVM) method for current control of voltage-source inverter. Unlike the conventional method using a limited number of voltage vectors by switching states, the proposed method can consider various voltage vectors to identify the optimized voltage vector. The various voltage vectors are obtained by subdividing existing voltage vectors. The optimized voltage vector that minimizes the cost function is selected and applied to the inverter by using the SVM. The various voltage vectors and SVM reduce current ripples in the output AC side of the inverter compared with the conventional method. The effectiveness and performance of the proposed method are verified through simulation and experiment with a three-phase two-level voltage-source grid-connected inverter.

• Journal of Power Electronics
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• v.18 no.2
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• pp.522-532
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• 2018

The cascaded H Bridge (CHB) multilevel inverter (MLI) is popular among the classical MLI topologies due to its modularity and reliability. Although space vector modulation (SVM) is the most suitable modulation scheme for MLIs, it has not been used widely in industry due to the higher complexity involved in its implementation. In this paper, a simple and novel generalized SVM algorithm is proposed, which has both reduced time and space complexity. The proposed SVM involves the generalization of both the duty cycle calculation and switching sequence generation for any n-level inverter. In order to generate the gate pulses for an inverter, a generalized switch matrix (SM) for the CHB inverter is also introduced, which further simplifies the algorithm. The algorithm is tested and verified for three-phase, three-level and five-level CHB inverters in simulations and hardware implementation. A comparison of the proposed method with existing SVM schemes shows the superiority of the proposed scheme.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.4
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• pp.303-310
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• 2020

Estimating the accurate internal state of lithium ion batteries to increase their safety and efficiency is crucial. Various algorithms are used to estimate the internal state of a lithium ion battery, such as the extended Kalman filter and sliding mode observer. A state-space model is essential in using algorithms to estimate the internal state of a battery. Two principal methods are used to express the state-space model, namely, continuous time and discrete time. In this work, the extended Kalman filter is employed to estimate the internal state of a battery. Moreover, this work presents and analyzes the estimation performance of algorithms consisting of a continuous time state-space model and a discrete time state-space model through static and dynamic profiles.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.64-71
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• 2008

This study is on pedestrian protection device using pneumatic cylinder and simple link mechanism when vehicle collide with pedestrian. This study ensured the safety space between engine and hood after it applies to simple link mechanism and pneumatic cylinder. It can absorb the damage which measure the specific device if vehicle collide with pedestrian. Combination of simple link mechanism and pneumatic cylinder was more superior than the present pedestrian protection device. Simple link mechanism could confirm superior height and survival probability than when only cylinder operated. It also ensured enough space between engine and hood. And if a cylinder is not working because of old cylinder, poor repair or damage of accident vertical cylinder would be difficult to execute because there exists the irregular space between engine and hood. If simple link mechanism operates with only one cylinder it could ensure the regular space because simple link mechanism set up at the middle of hood. So this device could confirm high safety for pedestrian.

• Journal of Korea Multimedia Society
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• v.15 no.7
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• pp.903-909
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• 2012

In this paper, we analyze the sharing performances for coexistence of different communication systems between adjacent channels in TV White space. We analyze the parameter performance result according to various density of interfering transmitter and transmitter output. Two cases are analyzed to consider an interference effect between each system. First, WiBro is an interfering transmitter and WLAN is a victim receiver. Second, WLAN is an interfering transmitter and WiBro is a victim receiver. Free space channel model, Extended Hata and IEEE 802.11 model are used for channel environment. Analyzed coexistence results under various co-use scenarios may be widely applied into the technique developed to get the coexisting condition for wireless devices using many communication protocols in adjacent frequency.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.1
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• pp.1-10
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• 2002

In this paper the space voltage vector pulsewidth modulation(SVPWM) technique for two-phase inverter is proposed. The two-phase SVPWM technique is applicable to two-phase induction motor drives. The two-phase inverter using two-phase SVPWM technique cannot generate zero voltage vectors, but four space vectors. A reference voltage vector in the square locus is realized by adjusting four space vectors. The switching sequence "two-phase symmetrical modulation" used in two-phase SVPWM is proposed. Practical verification of theoretical predictions is presented to conform the capabilities of the new technique.technique.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.4
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• pp.332-338
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• 2007

In this paper, the three modified space vector modulation methods are suggested in order to control effectively the shoot-through time at Z-source inverter. Both the switching patterns of three modulation methods and the modulation signals with a variation of shoot-through time are analyzed. The optimum modified space vector modulation method is determined by both the control range of the shoot-through time and the symmetry of the switching pattern and modulation signal. The performances of modulation methods are verified with the simulation results with 32-bit DSP.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1500-1511
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• 2017

The purpose of this paper is to study a high-performance control scheme for neutral-point-clamping three-level (NPC-3L) inverter fed dual three-phase permanent magnet synchronous motor (PMSM) drives by considering some asymmetric factors such as the non-identical parameters in phase windings. To implement this, the system model is analyzed for dual three-phase PMSM drives with asymmetric factors based on the vector space decomposition (VSD) principle. Based on the equivalent circuits, PI controllers with feedforward compensation are used in the d-q subspace for regulating torque, where the cut-off frequency of the PI controllers are set at the twice the fundamental frequency for compensating both the additional DC component and the second order component caused by asymmetry. Meanwhile, proportional resonant (PR) controllers are proposed in the x-y subspace for suppressing the possible unbalanced currents in the phase windings. A dual three-phase space vector modulation (DT-SVM) is designed for the drive, and the balancing factor is designed based on the numerical fitting surface for balancing the DC link capacitor voltages. Experimental results are given to demonstrate the validity of the theoretical analysis and the proposed control scheme.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.546-549
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• 2008

Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency(ISAS/JAXA) successfully developed and operated the microwave discharge ion engines onboard Hayabusa asteroid explorer. The ${\mu}10$ ion engines feature the cathode-less plasma generation in both the ion generators and neutralizers with the results of long life and high reliability in space. Based on the space achievements of ${\mu}10$ ion engines with 8mN thrust, 3,000sec Isp and 350W consumption power, several programs are currently under developments: ${\mu}20$, ${\mu}10$HIsp and ${\mu}1$. The first is a 20-cm diameter microwave discharge ion engine, aiming to achieve 30mN/kW in the thrustto-power ratio for the asteroid sample return mission larger than Hayabusa. The second is a high Isp version of ${\mu}10$, and exhausts the plasma beam over 10,000sec Isp using 15kV acceleration voltage for deep space missions to such as Jupiter and Mercury. The third is ${\mu}1$ to be adapted to small satellites for drag-free.