Performance of several types of fuel cells and factor analysis of performance

There are four types of fuel cells: Polymer Electrolyte Fuel Cells (PEFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), and Solid Oxide Fuel Cells (SOFC). The performance of these fuel cells has not been compared. Equations that are able to express the performance of these fuel cells accurately were derived or modified from the latest published performance data. The cell voltages of the four fuel cells were estimated by these equations, resulting in high‐temperature fuel cells such as MCFC and SOFC having higher energy conversion efficiencies than low‐temperature fuel cells such as PEFC and PAFC. This difference originates from low cathode polarization, overcoming both a decrease of open circuit voltage with increasing temperature and higher Nernst losses for high‐temperature fuel cells of approximately 85 mV than those for low‐temperature fuel cells due to steam generation in the anode chamber in the high‐temperature fuel cells. A generalized relationship between cell voltage and operating temperature was derived, stating that the cell voltage is almost constant between 500 °C and 1000 °C. A fuel cell which has protons as a migration species in the electrolyte and works between 250 °C and 500 °C would give a performance comparable with high‐temperature fuel cells due to lower Nernst losses than those for high‐temperature fuel cells. © 2001 Scripta Technica, Electr Eng Jpn, 138(1): 24–33, 2002     

An empirical I‐V model of tunneling real‐space transfer transistors for monostable–bistable transition logic element application

We proposed an empirical I‐V model to represent the negative differential resistance (NDR) regime of fabricated tunneling real‐space transfer transistors (TRSTTs). For TRSTTs to have great potential in monostable–bistable transition logic element (MOBILE) design, our model is able to accurately reproduce the NDR regime including gate‐source‐bias‐controlled NDR values and modulated peak to valley drain current ratios. The modeled I‐V curves, tranconductances, and NDRs with multiple gate biases are in good agreement with measured data. The key parameters in the model have clear physical meanings, and the value of these parameters is easy to be extracted directly from the test I‐V curves. The model is used to simulate a practical MOBILE, and excellent agreement between the simulated and measured data was found. Copyright © 2015 John Wiley & Sons, Ltd.     

A new modeling approach for circuit‐field‐coupled time‐stepping electromagnetic analysis of saturated interior permanent magnet synchronous motors

This paper proposes a new modeling approach for circuit‐field‐coupled time‐stepping electromagnetic analysis of a saturated interior permanent magnet synchronous motor (IPMSM). To predict the drive performance quickly, the proposed approach consists of a dynamic simulator based on a new analytical model of the d‐ and q‐axis magnetization characteristics (λ‐i_d‐i_q‐θ). The model can take into account not only cross‐saturation but also the harmonics of the inductance distributions and EMF waveforms. The validity of the model is verified from suitable simulation results for the instantaneous current and torque waveforms of the IPMSM. The proposed analysis leads to a dramatic reduction in the computation time compared to circuit‐field‐coupled time‐stepping FEA, while maintaining analytical accuracy. The effectiveness of the proposed method is experimentally verified using a 10‐kW, 15,000‐rpm concentrated‐winding IPM motor. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 49–58, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21024     

Two‐dimensional non‐stationary numerical model for MSM structures

In this paper the solution of the non‐stationary model for MSM structures is obtained numerically. The two‐dimensional model consists of three singularly perturbed non‐linear partial differential equations. The alternating‐direction method for discretization in time and the non‐oscillatory streamline upwind method on a piecewise uniform grid for discretization in space are used to eliminate the interior and boundary layer oscillations. The described model is used for the analysis of the time response of a GaAs n‐type MSM structure to a Heaviside function form of the applied voltage. For the stationary case the I–V characteristic of the structure is determined. The numerical results confirm that the applied method is convenient for solving convection–diffusion problems. Copyright © 1999 John Wiley & Sons, Ltd.     

Performance of a novel dot matrix fuel cell using an inorganic micro‐proton conductor

The power generation properties of a novel dot matrix fuel cell using an inorganic micro‐proton conductor were evaluated in dry gas mixtures of hydrogen and oxygen during room‐temperature operation. The single dot matrix fuel cell was composed of aggregates of micro‐electrolyte dots filling pores arranged in a matrix form on a Teflon or polyimide substrate with Pt/C and Pt catalytic electrodes. Micro‐electrolyte dots were prepared by the sol–gel method using titanium phosphorus oxides as the proton conductive hybrid materials. The open‐circuit voltage of the single cell became higher when using a small dot diameter and achieved a maximum of 500 mV with an electrolyte dot density of 17 dots/cm² in the dry gas mixtures during room‐temperature operation. This value corresponds to about one‐half of the theoretical electromotive force. Moreover, the current density of the single cell increased with the dot diameter such that it grew to 8 mA/cm² at a dot diameter of 500 µm. As a result, dot matrix fuel cells connected in series and parallel were found to achieve the cell performance of high‐energy density such as used by high‐energy microchips. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

平板式固体氧化物燃料电池Ni/YSZ阳极上甲烷重整过程实验研究

为了开发甲烷直接内部重整的高效固体氧化物(solid oxide fuel cell,SOFC)燃料电池系统,必须对阳极上甲烷水蒸气重整过程进行详细研究。文中搭建了实验台,对开发的平板式SOFC燃料电池多孔介质阳极上甲烷重整过程进行了实验研究。给出在不同燃料流量和不同水蒸气/甲烷比(S/C)工况下出口气体各组分的摩尔分数和甲烷转化率的分布。实验结果表明工作参数对甲烷的转化率有很大的影响,在相同工作温度下甲烷的转化率随着进口燃料流量增加而降低,因此出口气体中氢气的摩尔浓度也相应降低。另外通过分析实验结果,可见阳极的入口处最有可能有碳形成。     

Performance evaluation of SOFC systems using electrochemical partial oxidation of methane

We simulated the performance of systems using a solid oxide fuel cell (SOFC) stack which generates electricity by electrochemical partial oxidation of methane and a conventional steam‐reforming‐type SOFC (SRSOFC) stack. The net thermal efficiency in an atmospheric partial‐oxidation‐type SOFC (POSOFC)‐SRSOFC system was 8% higher than that in an atmospheric SRSOFC system at system outputs of 35 kW or more. The net thermal efficiency of a pressurized POSOFC‐SRSOFC‐gas turbine (GT) system was slightly higher than that of a pressurized SRSOFC‐GT system. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(4): 11–19, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10314     

Mapping of circuit variables into two‐port network variables in basic amplifier structures: identifying new topologies

In this paper, we report on a unique observation which enables the unification of the analysis for different amplifier structures. In particular, we report that the change from one type of amplifier to the other can be understood via a mapping of source‐load circuit variables (V_s, R_s, I_i, I_o, I_L, V_o) into two‐port network variables (V₁, V₂, I₁, I₂). As such, unified expressions for (A_v,Z_i,A_i,Z_o) are derived. Further, a Matlab code is written to search for all valid mappings out of 3⁸ different possibilities. Copyright © 2013 John Wiley & Sons, Ltd.     

Numerical simulation of blow‐down closed‐cycle disk MHD generator

Numerical simulations of the closed‐cycle disk MHD generation experiment with Tokyo Institute of Technology's Fuji‐1 blow‐down facility are performed. In the calculations, the r–z two‐dimensional time‐dependent simulation code developed by the authors that can take the effect of water contamination into account is used, and the experimental conditions of Run A4109 operated by Disk‐F4 generator are selected as the numerical conditions. When the water contamination is the lowest level realized in the experiments, the simulation results coincide with the experimental results reasonably well, though there exist some discrepancies caused by inaccuracy of used basic plasma parameters, limitations of the two‐dimensional approximation, and so on. The voltage–current curve is almost linear, indicating that the MHD interaction is relatively weak and the flow field is mainly determined by the back‐pressure. The increase of the water contamination level results in decreased seed ionization rate at the generator channel inlet, leading to the steep deterioration of the generator performance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 46–54, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10335     

Multiple operating points in a square‐root domain first‐order filter

In this paper novel corrective circuits to avoid multiple operating points in a square‐root domain first‐order filter are proposed. By employing a DC test it is demonstrated that the filter possesses three operating points (two stable and one unstable) and the corrective circuits enforce the proper operating mode. The corrective circuits and filter are able to operate with very low supply voltages (as low as V_GS+2V_DSsat). Moreover, a detailed analysis concerning the impact that produces the corrective circuits on the filter performance is discussed. Both measurement and simulation results are provided to validate the circuits and analysis employed. Copyright © 2006 John Wiley & Sons, Ltd.     

Magnetic properties of Pr‐Fe‐Co‐V‐W‐Si‐B system exchange spring magnets

The melt‐spun ribbons of Pr‐Fe‐Co‐V‐W‐Si‐B system alloys were prepared by single roller rapid‐quenching method. The effects of composition, surface velocity, and heat treatment on the magnetic properties were investigated. The P₉sFe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy ribbons prepared at a surface velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat‐treatment condition was found to be at 575°C for 3 min, for which the magnetic properties were (BH)_max = 136.1 kJ/m³, J_r = 0.93 T, H_cJ = 652.2 kA/m, and H_cB = 528.3 kA/m. The temperature coefficients of J_r and H_cJ for the ribbons crystallized from melt‐spun ribbons of Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy were α(J_r)_ave = ?0.057%/°C and α(H_cJ) = ?0.450%/°C. The value of (B)_max for the compression molding Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 isotropic bonded magnet prepared by using the ribbons annealed at 575°C for 3 min is 80.0 kJ/m³, and the density is 6.24 Mg/m³. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 10–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20211 Copyright © 2006 Wiley Periodicals, Inc.     

Combined carbon‐dioxide‐capturing high‐performance power generation system using a solid oxide fuel cell operating on pressurized fuel/air

The authors recently proposed a high‐performance combined carbon‐dioxide‐capturing power generation system using a solid oxide fuel cell (SOFC) and a closed‐cycle MHD generator, in which pure oxygen is used as the oxidant. This combined system makes the best use of the advantages of combustion with pure oxygen but fails to prevent the efficiency deterioration caused by high power demand for oxygen production. In the present study, the authors modified this previous system and proposed an improved combined carbon‐dioxide‐capturing power generation system using SOFC/MHD characterized by a higher overall thermal efficiency. In this system, pure oxygen is supplied only to the combustor to reduce the power required for the oxygen production, and pressurized air is used as the oxidant gas in the SOFC. The power saving amounts to about 5% of the thermal input, resulting in a very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value of the overall thermal efficiency of carbon‐dioxide‐capturing systems. Advantages of the proposed system suggest that it is advisable to continue further research in this direction. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 21–30, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20010     

Cycle analysis using exhaust heat of SOFC and turbine combined cycle by absorption chiller

The power generating efficiency of solid oxide fuel cell (SOFC) and gas turbine combined cycle is fairly high. However, the exhaust gas temperature of the combined cycle is still high, about 300^°C. Thus, it should be recovered for energy saving, for example, by absorption chiller. The energy demand for refrigeration cooling is recently increasing year by year in Japan. We propose here a cogeneration system by series connection of SOFC, gas turbine and LiBr absorption chiller to convert the exhaust heat to the cooling heat. As a result of cycle analysis of the combined system with 500‐kW‐class SOFC, the bottoming single‐effect absorption chiller can produce a refrigerating capacity of about 120 kW, and the double‐effect absorption chiller can produce a little higher refrigerating capacity of about 130 kW without any additional fuel. But the double‐effect absorption chiller became more expensive and complex than the single‐effect chiller. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 49– 55, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20578     

CMOS Non‐tailed differential pair

A continuous‐time complementary metal–oxide–semiconductor differential pair that does not require the traditional tail current source as a way to control the direct current and common‐mode current is presented. Compared with a p‐channel long‐tailed pair, the proposed non‐tailed solution operates under a higher maximum input common‐mode voltage that includes (V_DD + V_SS)/2 even under low supply voltages. Experimental measurements on a prototype fabricated in a 0.35‐µm technology (with metal – oxide – semiconductor thresholds greater than 0.6 V) confirm this behavior for supply voltages as low as 1.2 V, whereas the long‐tailed pair with the same technology offers the same capability only for supplies higher than 1.6 V. Copyright © 2015 John Wiley & Sons, Ltd.     

Insulation characteristics of GIS under nonstandard lightning‐impulse oscillations: Insulation characteristics under single‐frequency oscillations with various frequencies and damping ratios

To improve GIS insulation specifications, it is important to recognize the insulation characteristics under oscillatory overvoltage waveforms occurring in the field. This paper describes investigations of insulation characteristics for single‐frequency oscillatory waveforms with various frequencies and damping ratios. It was found that minimum breakdown voltages (V_min) rose with frequency rising under the same damping condition and V_min rose with damping ratio rising under the same frequency condition. From an analysis of actual breakdown voltage characteristics, the probability of breakdown at a valley of oscillation rose with damping increasing. It was found that the insulation characteristics were treated all‐inclusively based on the characteristics of V_min for rise time or damping time. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(3): 43–49, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10156     

Proposal of a high‐performance solid oxide fuel cell combined power generation system with carbon dioxide recovery

A new fossil‐fuel‐utilized high‐performance combined power generation system with liquefaction recovery of carbon dioxide is proposed. In the system, pure oxygen is used as the oxidant gas to prevent the mixture of nitrogen in the exhaust gas and to make the liquefaction recovery of carbon dioxide possible. Solid oxide fuel cell is selected as the topping cycle. The exhaust fuel gas of the solid oxide fuel cell is afterburned with its exhaust oxidant gas of pure oxygen and the heat of the combustion gas is utilized in the bottoming cycle. Nonequilibrium MHD/noble gas turbine cycle is selected as the bottoming cycle because the temperature of the combustion gas reaches about 2300 K. It is made clear through detailed examination of energy balance that the total thermal efficiency of the system using natural gas (methane) as the fuel reaches 63.24% (HHV) or 70.18% (LHV). This efficiency is very high as for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance, and further research and development is warranted. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 12–21, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10146     

Single‐stage single‐switch PFC converter for wide‐input extreme step‐down voltage applications

This paper presents a new single‐stage single‐switch high power factor correction AC/DC converter suitable for low‐power applications (< 150 W) with a universal input voltage range (90–265 V_rms). The proposed topology integrates a buck–boost input current shaper followed by a buck and a buck–boost converter, respectively. As a result, the proposed converter can operate with larger duty cycles compared with the existing single‐stage single‐switch topologies, hence, making them suitable for extreme step‐down voltage conversion applications. Several desirable features are gained when the three integrated converter cells operate in discontinuous conduction mode. These features include low semiconductor voltage stress, zero‐current switch at turn‐on, and simple control with a fast well‐regulated output voltage. A detailed circuit analysis is performed to derive the design equations. The theoretical analysis and effectiveness of the proposed approach are confirmed by experimental results obtained from a 100‐W/24‐V_dc laboratory prototype. Copyright © 2011 John Wiley & Sons, Ltd.     

An equivalent‐circuit modelling on vertical and horizontal integrations for MOS flat‐band voltage simulation

The fixed oxide charge will cause the MOS capacitor (MOS‐C) flat‐band voltage to shift. We can observe the potential distribution to determine the MOS‐C flat‐band voltage. However, the potential distribution can be obtained from the integration of the electric field distribution. The integration of the electric field distribution is classified into the vertical and horizontal integrations. In this paper, we use the equivalent‐circuit model to demonstrate the flat‐band voltage of the non‐ideal MOS‐C. The equivalent‐circuit model of Poisson's equation includes two fixed charges Q′_f1 and Q′_f2 in the oxide layer region. Because the horizontal integration method is the superposition method, the equivalent‐circuit model for the horizontal integration is divided into 3 types. Hence, the flat‐band voltage for the horizontal integration is equal to the sum of the V_G1, V_G2, and V_G3 for the flat‐band condition. By comparison, the simulation results of the horizontal integration method approximate to the vertical integration method. Copyright © 2006 John Wiley & Sons, Ltd.     

基于混合pi-sigma神经网络的固体氧化物燃料电池建模

针对固体氧化物燃料电池(SOFC)建模难的现状,提出了一种基于混合pi-sigma神经网络建模的新方法.该方法通过在线修正隶属函数和结论参数,使得网络能够自主、迅速有效地收敛到要求的输入和输出关系,从而达到精确建模的目的.利用不同文献的实验数据,分别建立反应气体压力、电池温度、燃料气体组成及燃料利用率多变量的SOFC模型.应用仿真对该建模的有效性和建模精度进行了检验.最后在该混合pisigma神经网络辨识模型的基础上,分析了不同工作参数对sDFC工作性能的影响.     

Fast and accurate analysis of one‐dimensional arrays of dynamic PWL cells

This paper describes a new method for the time‐domain analysis of one‐dimensional arrays of dynamic piecewise linear cells. The method exploits the local connectivity, typical of cellular arrays, and the piecewise linear behaviour of the v–i characteristic of the non‐linear elements to obtain a piecewise analytical expression of the solution. Examples demonstrate the accuracy and the efficiency, in terms of CPU‐time, of the proposed method with respect to standard simulation tools as SPICE and the numerical integration of a system of ordinary differential equations. Copyright © 2001 John Wiley & Sons, Ltd.