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박봉희(Park, Bong-Hee),김승민(Kim, Seung-Min),최주엽(Choi, Ju-Yeop),최익(Choy, Ick),이상철(Lee, Sang-Chul),이동하(Lee, Dong-Ha) 한국태양에너지학회 2013 한국태양에너지학회 학술대회논문집 Vol.2013 No.4
This paper proposes a modeling of fuel cell which replaces dc source during simulation. Fuel cells are electrochemical devices that convert chemical energy in fuels into electrical energy. This system has high efficiency and heat, no environmental chemical pollutions and noise. Proton exchange membrane fuel cells(PEMFC) are commonly used as a residential generator. These fuel cells have different electrical characteristics such as a low voltage and high current compared with solar cells. And there are different behaviors in the V-I curve in the temperature and pressure. Therefore, the modeling of fuel cell should consider wide voltage range and slow current response and the resulting electrical model is applied to power converter system(PCS) with fuel cell as an input source.
박봉희(Park Bong-Hee),최주엽(Choi Ju-Yeop),최익(Choy Ick),이상철(Lee Sang-Cheol),이동하(Lee Dong-Ha) 한국태양에너지학회 2014 한국태양에너지학회 논문집 Vol.34 No.1
This paper proposes a modeling of fuel cell which replaces dc source during simulation. Fuel cells are electrochemical devices that convert chemical energy in fuels into electrical energy. This system has high efficiency and heat, no environmental chemical pollutions and noise. Proton exchange membrane fuel cells(PEMFC) are commonly used as a residential generator. These fuel cells have different electrical characteristics such as a low voltage and high current compared with solar cells. And there are different behaviors in the V-Icurve in the temperature and pressure. Therefore, the modeling of fuel cell should consider wide voltage range and slow current response and the resulting electrical model is applied to boost converter with fuel cell as an input source.
태양광 / 연료전지용 배터리 충·방전 하이브리드 시스템 설계
박봉희(Park Bong-Hee),조영민(Jo Yeong-min),최주엽(Choi Ju-Yeop),조상윤(Cho Sang-Yoon),최익(Choy Ick),이동하(Lee Dong-Ha) 한국태양에너지학회 2014 한국태양에너지학회 논문집 Vol.34 No.4
Photovoltaic and fuel cell systems can be used as power source in mobile robots. At this time the photovoltaic system generally generate power in daytime. The starting time of fuel cell is slower than the lithium battery. To compensate for these disadvantages, a battery charge-discharge system is used. Especially the bi-directional converter is used mainly in the charge-discharge method. The controller in a buck converter controls the input voltage of the converter to meet the maximum power point tracking(MPPT) performance. First of all, the simulations of hybrid system for battery charge-discharge system in each step simulated using solar and fuel cell modeling as input source in PSIM. Experiment of the buck and bi-directional converter system is conducted through using photovoltaic/fuel cel simulator(pCube) instead of solar and fuel cell. This hybrid system for battery charge·discharge using photovoltaic/fuel cell generates emergency power for the communication system in mobile robot.
박봉희(Park, Bong-Hee),김승민(Kim, Seung-Min),최주엽(Choi, Ju-Yeop),최익(Choy, Ick),이상철(Lee, Sang-Chul),이동하(Lee, Dong-Ha),이영권(Lee, Young-Kwon) 한국태양에너지학회 2013 한국태양에너지학회 논문집 Vol.33 No.6
This paper proposes DC offset current compensation method of transformerless fuel cell/PV PCS. DC offset current is generated by the unbalanced internal resistance of the switching devices in full bridge topology. The other cause is the sensitivity of the current sensor, which is lower than DSP in resolution. If power converter system has these causes, the AC output current in the inverter will generate the DC offset. In case of transformerless grid-connected inverter system, DC offset current is fatal to grid-side, which results in saturating grid side transformer. Several simulation results show the difficulties of detecting DC offset current. Detecting DC offset current method consists of the differential amplifiers and PWM is compensated by the output of the Op amp circuit with integrator controller. PSIM simulation verifies that the proposed method is simpler and more effective than using low resolution current sensor alone.
박봉희(Park Bong-Hee),김승민(Kim Seung-Min),최주엽(Choi Ju-Yeop),최익(Choy Ick),이상철(Lee Sang-Cheol),이동하(Lee Dong-Ha),이영권(Lee Young-Kwon) 한국태양에너지학회 2013 한국태양에너지학회 학술대회논문집 Vol.2013 No.11
This paper proposes DC offset current compensation method of trans-less fuel cell/PV PCS. DC off set current is generated due to the unbalanced internal resistance of the switching devices in full bridge topology. The other cause of DC off set current is that the sensitivity of the current sensor is lower than the resolution of the DSP. If inverter is controlled by the current including DC offset, it"s AC output current will generate DC offset. In case of trans-less grid-connected inverter system, DC offset current is fatal to grid, which results in saturating grid side transformer. Several simulation results with different unbalanced conditions show the difficulties of detecting of DC offset current. Op amp circuit detecting DC offset current functions both amplifier and differential. It provides compensated DC offset component PWM circuit. PSIM simulation verifies that the proposed method is simpler and more effective than using low resolution current sensor alone.
Distributed Queue를 이용한 서버 가용성 향상 연구
박봉희 ( Bonghee Park ),최진영 ( Jinyong Choi ) 한국정보처리학회 2014 한국정보처리학회 학술대회논문집 Vol.21 No.1
기업에서 사용하는 시스템에서는 대량의 데이터를 실시간으로 처리해야 하며 또한 시스템 장애로 인한 생산 중단이 발생하지 않도록 하기 위해 서버 이중화 구성에 많은 투자를 하고 있다. 장애를 최소화하기 위해 서버 구성을 Active-Standby 구조로 이중화를 구성하여 사용하고 있으며,이로 인해 시스템에 대한 많은 비용을 투자하고 있다. 서버 부하 감소 및 서버 가용성 향상을 통한 투자 비용을 절감하기 위해 서버 분산 처리에 대한 방법이 나오고 있다,그러나 Network 스위치나 라우터 등의 Hardware 적인 분산 시스템을 이용한 방법으로는 특정한 데이터만을 분산하여 처리할 수 없고 Hardware의 투자 비용 또한 증가하게 된다. 또한 서버의 Active-Standby 구성에서 Standby 서버는 Active 서버의 문제 발생시에만 이용하게 됨으로 인해 서버의 가용성이 떨어지는 불합리가 발생함으로 인해 이를 개선하기 위한 연구를 통해 Active-Active 구성을 통해 서버의 가용성을 확보하고자 한다. 본 논문에서는 서버 가용성 향상을 위한 방법으로 DQ(Distributed Queue)를 이용하여 응용프로그램에서의 데이터 분산을 통한 응용프로그램에서의 부하를 분산하여 서버 내 리소스를 최대한 활용하면서 응용 프로그램에서의 부하를 감소화할 수 있는 방법을 검증하고자 한다.
박봉희(Park Bong-Hee),정승환(Seung-Whan Jeon),최주엽(Ju-Yeop Choi),최익(Choy Ick),이상철(Lee Sang-Cheol),이동하(LeeDong-Ha) 한국태양에너지학회 2014 한국태양에너지학회 논문집 Vol.34 No.2
Generally, buck converter controller is designed to control the output voltage of the converter. However, design of the controller in a photovoltaic power conditioning system is different from theoretical design guideline. The controller in a photovoltaic power conditioning system controls the input voltage of the converter (the output voltage of the solar cell) to meet a maximum power point tracking (MPPT) performance. In this study, a new model for buck converter used in a photovoltaic power conditioning system is proposed, which is linearized after state-space averaging in each period. Also, mathematical expression of the modeled buck converter is interpreted separately as small and large signals; therefore its appropriateness is measured to design linear voltage and current controller.