• 한국통신학회논문지
• /
• 제22권4호
• /
• pp.696-705
• /
• 1997

This paper presents an efficient adaptive predistortion technique compensating linear and nonlinear distortions caused by high-power amplifier (HPA) with memory in OFDM systems. The efficient adaptive data predistortion techniques proposed for compensation of HPA with memory in single carrier systems cannot be applied to OFDM systems since the possible input levels for HPA is infinite in OFDM systems. Also, previous adaptive predistortion techniques, based on Volterra series modeling, are not suitable for real-time implementation due to high computational burden and slow convergence rate. In the proposed approach, the memoryless HPA preceded by a linear filter in OFDM systems is modeled by the Wiener system which is then precompensated by the proposed adaptive predistorter with a minimum number of filter taps. An adaptive algorithm for adjusting the proposed adaptive predistorter is derived using the stochastic gradient method. It is demonstrated by computer simulation that the performance of OFDM system suffering from nonlinear distortion can be greatly improved by the proposed efficient adaptive predistorter using a small number of filter taps.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
• /
• pp.147-150
• /
• 2004

본 논문에서는 분산전원 계통을 모의하기 위한 시뮬레이터의 설계와 시험에 대한 내용을 제시하고자 한다. 제시하고자 하는 시뮬레이터는 RTDS(Real Time Digital Simulator)와 전력 증폭기(power amplifier)로 구성된다. RTDS 부분은 분산전원이 적용되는 계통의 모의와 분산전원의 전원부 모의를 위해 사용되며 전력 증폭기는 RTDS에 의해 모의된 전력 계통의 모선 전압 출력과 분산전원 전원부의 전압 출력을 증폭하기 위하여 사용된다. 시뮬레이터 구성을 위해 사용되는 RTDS의 구성과 제작된 전력 증폭기의 사양과 동작시험에 대한 결과를 제시하고자 한다. 개발된 시뮬레이터는 분산전원의 동적 및 정적 성능 평가를 위한 시험 시스템 개발에 적용될 수 있다.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
• /
• pp.1483-1485
• /
• 2005

In recent years, customers and power supplies are interested in power quality. Demands of customers are change from standard quality of distribution power system to various high quality of distribution power system. so, it is necessary to apply power quality compensator. in our project, we develop the UPQC(Unfied Power Quality Compensator of 45kVA which compensates power factor and voltage sag, interruption. it is very frequently occurred power quality problems. As a series and shunt compensator, UPQC consists of two inverters with common dc link capacitor bank. It compensates the current quality in the shunt part and the voltage quality in the series part. In this paper, we present simulation and test result of developed UPQC system. Test for UPQC are performed at voltage sag, flickers and non-linear load conditions. For voltage sag and ficker generation, we use RTDS(Real Time Digital Simulator) and power amplifier system.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 A
• /
• pp.350-352
• /
• 1995

The starting characteristics of single phase induction motor(SPIM) is described by control of phase and voltage. Auxiliary winding voltage is controlled by DC amplifier and phase is integrator. These processes enable comparison of torque with slip in each voltage and phase angle variations. Simulation and experimentation results of the motor's torque-slip characteristics using the controlled auxiliary winding voltage and phase angle arc shown and discussed. As a results, starting time is fast and main winding current is small when auxiliary winding voltage is low than rating voltage and starting characteristics is good in phase angle $90^{\circ}$.

• 한국광학회지
• /
• 제11권3호
• /
• pp.166-170
• /
• 2000

고리형 광섬유 공전기 안에 반도체 광 증폭기를 삽입하여 1530 nm에서 1570까지 파장을 가변할수 있는 전광 동기 신호 재생 방식을 제안하고 구현하였다. 임의 파형을 갖는 10 Gbps와 30 Gbps 광 펄스열로부터 injection locking 방법에 의해 동기화된 광 펄스열을 재생하였다. 또한, 대신호 시영역 모델링을 이용하여 입력 광 펄스열의 평균 파워의 변화, 섭동에 대한 시스템의 반응을 해석하였다.

• Journal of Magnetics
• /
• 제17권3호
• /
• pp.206-209
• /
• 2012

Peak interval for reversible permeability is presented for nondestructively evaluating the remanent life of 1Cr-0.5Mo steel. The method to measure the peak interval of reversible permeability is based on the value of reversible permeability is the same as the differential value of the hysteresis loop. The measurement principle is based on the first harmonics voltage induced in a sensing coil using a lock-in amplifier tuned to a frequency of the exciting voltage. Results obtained for the peak interval of reversible permeability and Rockwell hardness on the aged samples decrease as aging time and the Larson-Miller parameter increase. We could estimate the remanent life of 1Cr-0.5Mo steel by using the relationship between the peak interval of reversible permeability and the Larson-Miller parameter, nondestructively.

• Journal of Magnetics
• /
• 제16권1호
• /
• pp.42-45
• /
• 2011

The present work studies a nondestructive evaluation of the degradation of modified 9Cr-1Mo steel using a magnetic method based on the existence of the peaks of reversible permeability (RP) in the differential magnetization around the coercive force. The apparatus is based on detection of the voltage induced in a coil using a lock-in amplifier tuned to the frequency of the AC perturbing field. Results obtained for the reversible permeability and Vickers hardness on the aged samples showed the peak interval of reversible permeability (PIRP) and Vickers hardness decrease as aging time increased. The correlation between Vickes hardness and the PIRP could be used to evaluate degradation of modified 9Cr-1Mo steel.

• ETRI Journal
• /
• 제41권4호
• /
• pp.426-436
• /
• 2019

In time division duplex (TDD)-based multiuser massive multiple input multiple output (MIMO) systems, the uplink channel is estimated and the results are used in downlink for signal detection. Owing to noisy uplink channel estimation, the downlink channel should also be estimated for accurate signal detection. Therefore, recently, a blind method was developed, which assumes the use of a linear high-power amplifier (HPA) in the base station (BS). In this study, we extend this method to a scenario with a nonlinear HPA in the BS, where the Bussgang decomposition is used for HPA modeling. In the proposed method, the average power of the received signal for each user is a function of channel gain, large-scale fading, and nonlinear distortion variance. Therefore, the channel gain is estimated, which is required for signal detection. The performance of the proposed method is analyzed theoretically. The simulation results show superior performance of the proposed method compared to that of the other methods in the literature.

• International journal of advanced smart convergence
• /
• 제11권2호
• /
• pp.53-58
• /
• 2022

In this paper, w-band frequency synthesizer was developed for frequency-modulated continuous wave (FMCW) radar sensors. To achieve a small size and high performance, We designed and manufactured w-band MMIC chips such as up-converter one-chip, multiplier, DA (Drive Amplifier) MMIC(Monolithic Microwave Integrated Circuit), etc. And interposer technology was applied between the W-band multiplier and the DA MMIC chip. As a result, the measured phase noise was -106.10 dBc@1MHz offset, and the frequency switching time of the frequency synthesizer was less than 0.1 usec. Compared with the w-band frequency synthesizer using purchased chips, the developed frequency synthesizer showed better performance.

• 대한전자공학회논문지
• /
• 제23권6호
• /
• pp.944-949
• /
• 1986

By improving the ability of arithmatic processing with an arithmatic processor in a microcomputer and realizing the data input system for real time analysis, an FFT analyzer that is usable within the range of audio frequency is designed and constructed. The input signal passes through a gain programmable pre-amplifier and anti-aliasing lowpass filter into an analogditital converter to be converted into digital form. The converted input data is processed by an Apple II microcomputer. The results of the processing are displayed using a microcomputer display unit and can be copied on a printer or stored in a floppy disk.