Problem Of Power Loss Research Articles

Shunt current calculation of fuel cell stack using Simulink ®

Presence of shunt current in fuel cell stacks can lead to corrosion and power loss problems. The objective of this paper is to develop a stack-level model for calculation of shunt currents. The simulation model was based on electrical circuit, and created using Simulink ® software. The Simulink ® results were validated by using PSpice ® software and comparing with experimental data of an electrolyzer stack. The Simulink ® model is also used to evaluate the effectiveness of a protective current method to reduce the shunt current. The protective current method was found to effectively reduce shunt current of a 100-cell stack. The Simulink ® model also shows that shunt current is highest at end cells of the 100-cell stack examined, suggesting extra care be applied to end cells for corrosion prevention. Monte Carlo simulation was performed to examine sensitivity of variance in voltage, manifold, channel and cell resistance on calculated shunt current. The sensitivity analysis shows that calculated shunt current is most sensitive to variance in manifold resistance and followed by variance in voltage, electrolyte and channel resistance. The calculated power loss due to shunt current is within 1% for the conditions examined.

4포트 동위상 고출력 전력결합기의 구현에 관한 연구

본 논문에서는 디지털 TV 중계기용 고출력 광대역의 3-Way 전력결합기를 설계.제작하였다. 대역폭 증가와 고출력을 동시에 이루기 위하여 Wilkinson 형태의 전력분배기를 채택하였다. 우선 Wilkinson 전력분배기를 균등(1 : 1) 및 비균등(2 : 1) 분배시켜, 동위상 4 포트 전력결합기를 시뮬레이션 하였다. 시뮬레이션 결과에 따라서 두께 120 mil인 유전체 기판을 사용하여 제작된 전력결합기는 디지털 TV 중계기 주파수 470~806 MHz 대역에서 삽입손실 -6.53dB 이하, 반사계수 -13dB 이하, 포트 간 분리도 -15 dB 이하, 출력 포트 간 위상차가 13<TEX>$^{\circ}$</TEX>이하의 특성을 보였다. 새롭게 만든 전력결합기는 회로에서의 고 임피던스로 인한 마이크로스트립 선로 폭의 한계와 고출력의 경우 선로간의 상호작용으로 인한 전력의 손실 및 협대역의 문제를 동시에 개선이 가능함을 알 수 있었다. 나아가서, 제작된 3-Way 결합기의 삽입손실, 반사계수, 포트간의 분리도 및 위상차가 디지털 TV 중계주파수 470~806 MHz에서 양호한 특성을 나타내는 것을 확인함으로써 고출력 및 광대역화가 실현가능하다는 것을 알 수 있었다. The broadband high power 3-way combiner was designed and fabricated for the digital TV repeater. To achieve increase of the bandwidth and the high power capability, Wilkinson type power divider was adopted in our research. First of all, Wilkinson type power divider of equal-split and unequal-split were combined, and the characteristics of the four port in-phase power combiner was simulated for each thickness of dielectric substrates. As the results of simulation, the power combiner fabricated by using dielectric substrate of 120 mil-thickness has the characteristics as follows: insertion loss of less than -651 dB, reflection coefficient of less than -13 dB, isolation among the output ports of less than -15 dB, and pose difference among the output ports of smiler than 13<TEX>$^{\circ}$</TEX>. Therefore, this power combiner was possible to improve the limit of microstrip line width due to high impedance, the problem of power loss due to interaction between strip lines in a high power combiner and narrow bandwidth simultaneously. Furthermore, making broadband and high power could be achieved since the fabricated 3-way combiner has good characteristics of insertion loss, the reflection coefficient, separation between ports, and phase difference.

Optical Super-Resolution Pickup Using a Liquid Crystal Shutter for CAD-MSR Magnetooptical Disk

We demonstrated characteristics of an optical super-resolution pickup using a liquid crystal (LC) shutter as a shading plate. The problem of laser power loss was solved by an LC shutter which was turned off for writing and turned on for reading. Combining this with CAD-MSR disk, we obtained good signals of high-density recording. This combination increases efficiency of laser power and does not require a slit to eliminate side-lobes. The laser power efficiency for writing is as high as 34% and linear bit density reaches 0.255 μm/bit even with a wavelength of 680 nm and an objective lens NA of 0.60.

A high-frequency downhole sparker sound source for crosswell seismic surveying

Traditionally seismic exploration techniques have not been widely used in hard rock mining and exploration environments. To facilitate faster and more accurate shallow high-resolution seismic surveys a high-frequency electric discharge (sparker) seismic source was developed. The main design requirements of this source were that it (1) achieve rapid downhole firing, (2) fit down surface diamond drill holes (70mm diameter), (3) provide similar energy level and frequency content to a seismic detonator so as to produce useful sharp signals over a distance up to 200 meters, and (4) it should be highly repeatable and reliable.The sparker system consists of a surface control and power source, winch cable and depth encoder, and a downhole probe. The 22kg downhole probe, which has a diameter of 60mm and length of approximately 3m, produces a discharge energy output of 480J. The innovation with this sparker is that the 60μF 5000V discharge capacitor is contained within the downhole probe, thus overcoming the problem of significant power loss through the high resistance of the cable and the effects of inductance experienced by other surface capacitor arc discharge sources. The sparker described does not include a discharge chamber, but instead relies on the saline conditions of a fluid filled borehole to enable explosive plasma bubble formation to occur.Initial field tests in the hard rock environment of Kambalda Western Australia provided some very encouraging results. The ability of the sparker to operate in a borehole under hydrostatic heads in excess of 250m and to produce clearly received signal at distances in excess of 100m was demonstrated. The output signal of a single shot of the sparker compared very favourably with that produced by a seismic detonator under the same conditions. The firing rate in the field was found to be approximately 5 shots per minute. Repeatability of the signal was excellent.

On stationary tests in the presence of structural breaks

We examine the effect of a structural break on stationarity tests. It has been shown that stationarity tests suffer from size distortion problems if a structural break exists but is ignored. This problem parallels the power loss problem of unit root tests ignoring an existing break. Nonetheless, the distributions of stationarity tests are asymptotically invariant to the exclusion of the existing break under the alternative hypothesis of a unit root. Our results thus clarify the nature of the effects of a structural break on inference regarding integrated time series.