• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.157.2-157.2
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• 2012

Direct-conversion receivers often suffer from a DC-offset that is a by-product of the direct conversion process to baseband. In general, a basic approach to reduce the DC-offset is to do simple average of the baseband signal and remove the DC by subtracting the average. However, this gives rise to a residual DC offset which degrades the performance when the receiver adopts the coding schemes with high coding rates such as 8-PSK. Therefore, more advanced methods should be additionally required for better performance. While the training sequences are basically designed to have good auto-correlation properties to facilitate the channel estimation, they may be not good for the simultaneous estimation of the channel response and the DC-offset. Also the DC offset compensation under a bad condition does not give good results due to the estimation error. Correspondingly, the proposed scheme employs the two important points. First, the training sequence codes are divided into two groups by MSE(Mean Squared Errors) for estimating the channel taps and then SNR calculated from each group is compared to predefined threshold to do fine DC-offset estimation. Next, ON/OFF module is applied for preventing performance degradation by large estimation error under severe channel conditions. The simulation results of the proposed scheme shows good performances compared to the existing algorithm. As a result, this scheme is surely applicable to the receiver design in many communications systems.

• Journal of Power Electronics
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• v.13 no.6
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• pp.964-974
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• 2013

A modified direct torque control (DTC) method based on torque angle is proposed for interior permanent-magnet synchronous motor (IPMSM) drivers used in electric vehicles (EVs). Given the close relationship between torque and torque angle, proper voltage vectors are selected by the proposed DTC method to change the torque angle rapidly and regulate the torque quickly. The amplitude and angle of the voltage vectors are determined by the torque loop and stator flux-linkage loop, respectively, with the help of the position of the stator flux linkage. Furthermore, to satisfy the torque performance request of EVs, the nonlinear dead-time of the invertor caused by parasitic capacitances is considered and compensated to improve steady torque performance. The stable operation region of the IPMSM DTC driver for voltage and current limits is investigated for reliability. The experimental results prove that the proposed DTC has good torque performance with a brief control structure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.869-876
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• 2001

In modern wireless communication, it has been regarded as a important problem for the spectrum efficiency to utilize the limited frequency-resource efficiently. In addition, the system architecture has been designed for low cost, low power consumption and ultra-lightweight. In this paper, we directly modulated the BCPFSK with a superior spectrum efficiency using the DDS and applied the direct conversion to the system architecture. Finally, we designed a transceiver which has the 433 MHz BCPFSK output and evaluated the system performance. In the measured result, we know that as for spectrum and the power efficiency, BCPFSK method is better than conventional one. Also, the results of the designed system is 433.92 MHz in center frequency and about 33 dBc in carrier suppression ratio. And we get the better results in local oscillator leakage and the spurious of the ISM out-band the same as -69dBc and under 60dBc.

• 한국전기화학회:학술대회논문집
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• 2005.04a
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• pp.43-43
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• 2005

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.166-171
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• 2000

In modem wireless communication it has been regarded as a important problem for the spectrum efficiency to utilize the limited frequency-resource efficiently. In addition, the system architecture has bun designed for low cost, low power consumption and ultra-lightweight. In this paper, we directly modulated the BCPFSK with a superior spectrum efficiency using the DDS and applied the direct conversion to the system architecture. Finally, we designed a transceiver which has the 433 MHz BCPFSK output and evaluated the system performance.

• Journal of Power Electronics
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• v.18 no.6
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• pp.1634-1641
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• 2018

This study focuses on a high-performance direct active and reactive power controller design that is successfully applicable to three-phase pulse width modulation (PWM) AC/DC converters used in renewable distributed energy generation systems. The proposed controller can overcome the sluggish transient dynamic response of conventional controllers to rapid power command changes. Desired active and reactive powers can be thoroughly obtained at the end of each PWM period through a deadbeat solution. The proposed controller achieves an exact nonlinear cross-coupling decoupling of system power without using a predefined switching table or bang/bang hysteresis control. A graphical and analytical analysis that naturally leads to a control voltage vector selection is provided to confirm the finding. The proposed control strategy is evaluated on a 3 kW PWM AC/DC converter in the simulation and experiment.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.3
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• pp.270-278
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• 2013

This paper proposes a control method for high voltage direct current(HVDC) with modular multilevel converter (MMC) under unbalanced voltage conditions considering the submodule(SM)'s current capacity and circulating current. It is aimed to propose a control method in which the current peak value does not exceed the maximum value of HVDC-MMC by considering the current capacity of the SM under unbalance voltage conditions. And it analyzes the effect of the unbalanced voltage on circulating currents in MMC and then proposes a control method considering each component of circulating currents under unbalanced voltages. The effectiveness of the proposed controlling method is verified through simulation results using PSCAD/EMTDC.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1552-1554
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• 1998

TEC(Thermoelectric conversion) is direct conversion method between thermal energy and electric energy. We studied on the mechanical, electrical and thermal properties of thermoelectric module, made experimental thermoelectric generator with BiTe material and manufactured module tester for electric-thermal energy conversion.

• BMB Reports
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• v.44 no.2
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• pp.107-112
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• 2011

We have developed a biologist-friendly, stand-alone Java GUI application, IdBean, for ID conversion. Our tool integrated most of the widely used ID conversion services that provide programmatic access. It is the first GUI ID conversion application that supports the direct merging as well as comparison of conversion results from multiple ID conversion services without manual effort. This tool will greatly help biologists who handle multiple ID types for the analyses of gene or gene product lists. By referring to multiple conversion services, the number of failed IDs can be reduced. By accessing ID conversion service online, it will potentially provide the most up-to-date conversion results. The application was developed in modular form; however, it can be re-packaged into plug-in form. For the development of a bioinformatics analysis tool, the module can be used as a built-in ID conversion component. It is available at http://neon.gachon.ac.kr/IdBean/.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.4
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• pp.105-113
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• 2010

In this paper, a 1.485 Gbps video signal transmission system using the carrier frequency of 240 GHz band was designed and simulated. The sub-harmonic mixer based on Schottky barrier diode was simulated in the transmitter and receiver. Both of heterodyne and direct detection receivers were simulated for each performance analysis. The ASK modulation was used in the transmitter and the envelop detection method was used in the receiver. The transmitter simulation results showed that the RF output power was -11.4 dBm($73{\mu}W$), when the IF input power was -3 dBm(0.5 mW) at the LO power of 7 dBm(5 mW) in sub-harmonic mixer, which corresponds to SSB(Single Side Band) conversion loss of 8.4 dB. This value is similar to the conversion loss of 8.0 dB(SSB) of VDI's commercial model WR3.4SHM(220~325 GHz) at 240 GHz. The combined transmitter and receiver simulation results showed that the recovered signal waveforms were in good agreement to the transmitted 1.485 Gbps NRZ signal.