• 천문학논총
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• 제24권1호
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• pp.65-81
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• 2009

We present the performance test results of VLBI Correlation Subsystem (VCS) trial product which was being developed for 1 year from August 2007. It is a core component of Korea-Japan Joint VLBI Correlator (KJJVC). The aim for developing VCS trial product is to improve the performance of VCS main product to reduce the efforts and cost, and to solve the design problems by performing the preliminary test of the manufactured trial product. The function of VCS trial product is that it is able to process the 2 stations-1 baseline, 8 Gbps/station speed, 1.2 Gbps output speed with FX-type. VCS trial product consists of Read Data Control Board (RDC), Fourier Transform Board (FTB), and Correlation and Accumulation Board (CAB). Almost main functions are integrated in the FTB and CAB board. In order to confirm the performance of VCS trial product functions, the spectral analysis, delay compensation and correlation processing experiments were carried out by using simulation and real observation data. We found that the overflow problem of re-quantization after FFT processing was occurred in the delay compensation experiment. We confirmed that this problem was caused by valid bit-expression of the re-quantized data. To solve this problem, the novel method will be applied to VCS main product. The effectiveness of VCS trial product has been verified through the preliminary experimental results, but the overflow problem was occurred.

• International Journal of Advanced Culture Technology
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• 제3권1호
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• pp.90-100
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• 2015

Green technologies such as renewable energy resources, Electric Vehicles and Plug-in Hybrid Electric Vehicles (EVs/PHEVs), electric locomotives, etc. are continually increasing at the existing power network especially distribution levels, which are Medium Voltage (MV) and Low Voltage (LV). It can be noted that the increasing level of green technologies is driven by the reduction emission policies of carbon dioxide ($CO_2$). The green technologies can affect the quality of power, and hence its impacts of are analysed. In practical, the environment such as wind, solar irradiation, temperature etc. are uncontrollable, and therefore the output power of renewable energy in that area can be varied. Moreover, the technology of the EVs/PHEVs is still developed in order to improve the performance of supply and driving systems. This means that these developed can cause harmonic distortion as the control system is mostly used power electronics. Therefore, this paper aims to analyse the voltage variation and harmonic distortion in distribution power network in urban area in Europe due to the combination between wind turbine, hydro turbine, photovoltaic (PV) system and EVs/PHEVs. More realistic penetration levels of SSDGs and EVs/PHEVs as forecasted for 2020 is used to analyse. The dynamic load demands are also taken into account. In order to ensure the accurate of simulation results, the practical parameters of distribution system are used and the international standards such as Institute of Electrical and Electronics Engineers (IEEE) standards are also complied. The suggestion solutions are also presented. The MATLAB/Simulink software is chosen as it can support complicate modelling and analysis.

• 대한전자공학회논문지TC
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• 제48권11호
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• pp.60-66
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• 2011

LTE는 다양한 서비스 클래스를 가지고 QoS를 지원한다. 각각의 트래픽 클래스에 대해 BER 요구사항이 크게 다르다. 이는 다양한 클래스의 트래픽에 대해 전송 전력이 상이함을 의미한다. 본 논문에서는 우선순위와 목표 BER을 고려하여 서비스 클래스를 지원하는 새로운 LTE를 위한 스케줄러를 제안한다. CQI와 QCI에 의해 각 사용자당 크래픽 클래스에 대한 목표 BER로 부터 최소 전송 전력이 할당된다. 따라서 사용자의 과거 사용 전송율과 트래픽의 우선순위와 같은 다른 정보를 이용하여 점유 채널의 확률이 결정된다. 서비스 클래스 스케줄링의 시뮬레이션 결과는 최대전송율 및 비례균일과 비교될 것이다. 실험결과는 서비스 클래스 기반의 스케줄링이 전체 시스템 수율을 개선할 수 있음을 보여주고 있다.

• Journal of Electrical Engineering and Technology
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• 제9권5호
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• pp.1471-1481
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• 2014

This paper presents the new power dissipation model of individual switching device in a high-level modular multilevel converter (MMC), which can be mostly used in voltage sourced converter (VSC) based high-voltage direct current (HVDC) system and flexible AC transmission system (FACTS). Also, the voltage balancing method based on sorting algorithm is newly proposed to advance the MMC functionalities by effectively adjusting switching variations of the sub-module (SM). The proposed power dissipation model does not fully calculate the average power dissipation for numerous switching devices in an arm module. Instead, it estimates the power dissipation of every switching element based on the inherent operational principle of SM in MMC. In other words, the power dissipation is computed in every single switching event by using the polynomial curve fitting model with minimum computational efforts and high accuracy, which are required to manage the large number of SMs. After estimating the value of power dissipation, the thermal condition of every switching element is considered in the case of external disturbance. Then, the arm modeling for high-level MMC and its control scheme is implemented with the electromagnetic transient simulation program. Finally, the case study for applying to the MMC based HVDC system is carried out to select the appropriate insulated-gate bipolar transistor (IGBT) module in a steady-state, as well as to estimate the proper thermal condition of every switching element in a transient state.

• Journal of Power Electronics
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• 제17권3호
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• pp.821-834
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• 2017

This paper reports on a single-inductor multiple-output step-up converter with digital control. A systematic analog-to-digital-controller design is explained. The number of digital blocks in the feedback path of the proposed converter has been decreased. The simpler digital pulse-width modulation (DPWM) architecture is then utilized to reduce the power consumption. This architecture has several advantages because counters and a complex digital design are not required. An initially designed unit-delay cell is adopted recursively for the construction of coarse, intermediate, and fine delay blocks. A digital limiter is then designed to allow only useful code for the DPWM. The input voltage is 1.8 V, whereas output voltages are 2 V and 2.2 V. A co-simulation was also conducted utilizing PowerSim and Matlab/Simulink, whereby the 55 nm process was employed in the experimental results to evaluate the performance of the architecture.

• 한국정밀공학회지
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• 제28권12호
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• pp.1434-1440
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• 2011

In this paper, we assessed muscular activities of lower limbs and foot pressure for car and bus drivers according to operating three electronic pedals that we developed. To analyze drivers' physical exhaustion, muscular fatigue of lower limbs was evaluated. Eleven car drivers and six urban bus drivers were participated in this experiment. The virtual driving system was used for the real driving environment. The virtual driving system was comprised of a spring seat, a steering wheel, pedals (clutch, excel and brake pedals), a manual transmission and a virtual driving simulation. For the real vibration like situation on the road, six degree of freedom motion base system was used. Measured muscles were rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (Gn) muscles. For the quantitative muscular activities, integrated electromyography (IEMG) was analyzed. Muscular fatigues also were analyzed through the analysis of the median frequency. In addition, foot pressures were analyzed and compared through the peak and averaged pressure during the operating three developed electronic pedals. The experiments are conducted with total 17 drivers, 11 general public and 6 drivers. As a result of the analysis, electromyogram and fatigue analysis through intermediate frequency reduction for pedal-1 more efficient than other pedals. And foot pressure also was decreased. Consequently, we suggested the most efficient pedal and method to minimize the amount of cumulative fatigue.

• 한국인터넷방송통신학회논문지
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• 제19권5호
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• pp.55-62
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• 2019

본 논문에서는 K 사용자 MIMO 간섭 채널을 고려하였으며, 정보와 전력을 동시에 전송하는 SWIPT 시스템을 위한 송수신기 설계 방법에 대해서 다룬다. 그리고, 정보 수신 장치와 전력 수확 장치가 같은 수신기에 존재하는 SWIPT 시스템을 고려한다. 제안하는 방식에서는 신호대 누수 잡음비 (SLNR)를 비용 함수로 사용하고, 수확 전력에 대한 임계값을 만족하도록 송수신기를 설계한다. 즉, 수확 전력에 대한 제약 조건 하에서, SLNR을 최대화시키도록 송신단 프리코딩 벡터, 수신단 검파기 벡터, 전력 분배 상수를 동시에 설계한다. 컴퓨터 모의실험을 통하여, 제안하는 기법과 기존 기법의 신호 대 간섭 잡음비 (SINR) 성능을 비교하였다. 사용자 수, 송신 안테나 개수, 수신 안테나 개수 간의 특별한 제약 조건을 만족하는 경우, 제안하는 기법은 낮은 SNR에서 기존 기법보다 우수한 SINR 성능을 나타낸다는 것을 보였다. 또한, 특별한 제약 조건을 만족하지 못하는 경우에는, 제안 기법이 모든 SNR 범위에 대해서 기존 기법보다 더 우수한 성능을 나타낸다는 것을 보였다.

• 드라이브 ㆍ 컨트롤
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• 제17권4호
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• pp.141-151
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• 2020

The aim of this study was to analyze the safety factor of range-shift gear pairs on multi-purpose agricultural implement machinery for an optimal design of a transmission system. Gear-strengths such as bending and contact stress and safety factors were analyzed under three load conditions: an equivalent engine torque at plow tillage, a rated engine torque, and the maximum engine torque. Root and contact safety factor were calculated to be 3.88, 5.14, 2.24, 2.11, 2.21, 0.99 and 0.78, 0.94, 0.65, 0.68, 0.84, 0.85, respectively, under equivalent engine torque condition at the plow tillage. The root and contact safety factor were calculated to be 1.91, 2.53, 1.10, 1.04, 1.07, 0.48 and 0.55, 0.66, 0.46, 0.48, 0.59, 0.59, respectively, under rated engine torque condition. The root and contact safety factor were calculated to be 1.60, 2.11, 0.92, 0.87, 0.90, 0.40 and 0.51, 0.61, 0.42, 0.44, 0.54, 0.54, respectively, under the maximum engine torque condition. The multi-purpose agricultural implement machinery could be conducted under plow tillage operation. However, gear specifications for tooth surface need modification because the gear surface would be broken at all driving conditions as safety factors are lower than 1.

• 전력전자학회논문지
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• 제26권4호
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• pp.271-276
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• 2021

Arc fault detector based on multilevel DWT with analysis of high-frequency noise components over 100 kHz is proposed in this study to improve the performance in detecting serial arcs and distinguishing them from inverter noise in PV systems. PV inverters generally operate at a frequency range of 20-50 kHz for switching operation and maximum power tracking control, and the effect of these frequency components on the signal for arc detection leads to negative arc detection. High-speed ADC and multilevel DWT are used in this study to analyze frequency components above 100 kHz. Such high frequency components are less influenced by inverter noise and utilized to detect as well as separate DC series arc from inverter noise. Arc detectors identify the input current of PV inverters using a Rogowski coil. The sensed signal is filtered, amplified, and used in 800kSPS ADC and DWT analysis and arc occurrence determination in DSP. An arc detection simulation facility in UL1699B was constructed and AFD tests the proposed detector were conducted to verify the performance of arc detection and performance of distinction of the negative arc. The satisfactory performance of the arc detector meets the standard of arc detection and extinguishing time of UL1699B with an arc detection time of approximately 0.11 seconds.

• 전기전자학회논문지
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• 제26권2호
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• pp.271-279
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• 2022

본 논문은 플로팅 커패시터를 갖는 이중 인버터의 향상된 데드 타임 보상 기법을 제안한다. 플로팅 커패시터를 갖는 이중 인버터는 2-레벨 단일 인버터보다 전력 반도체가 6개가 추가된다. 전력 반도체의 수가 증가로 이중 인버터의 출력 전압은 추가된 전력 반도체의 도통 전압만큼 감소되며 출력 전류 품질은 전력 반도체에 의한 전압 강하와 데드 타임에 의해 저하된다. 본 논문에서 제안하는 기법은 이중 인버터의 데드 타임 및 전력 반도체의 도통 전압을 보상하여 전류 품질을 개선하고 추가적인 대역통과 필터를 이용한 고조파 보상 기법을 통해 데드 타임과 도통 전압 보상에 대한 오차를 추가 보상한다.