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Abstract: The authors develop two-dimensional and three-dimensional simulation codes of the transient response of the temperature distribution in the lithium ion secondary battery during a discharge cycle. At first, a two-dimensional simulation code for a cylindrical battery is developed, and the simulation results for a commercially available small size battery are compared with the corresponding experimental results. The simulation results of the transient temperature and voltage variations coincide very well with the experimental results. The simulation result of the temperature difference between the center of the battery body and the center of the battery side is also in reasonable agreement with the experimental result. Next, the authors develop a three-dimensional simulation code and perform numerical simulations for three large size prismatic batteries with the same capacity and different cross sectional shapes. It is made clear that selecting the battery with the laminated cross section has a remarkable effect on the suppression of the temperature rise in comparison with the battery with square cross section, whereas the effect of the lamination on the suppression of the temperature unevenness is unexpectedly small. These results indicate the accuracy and usefulness of the developed simulation codes. [Copyright &y& Elsevier]

Abstract: The authors have been engaged in numerical simulations of the planar type solid oxide fuel cell (SOFC) to make clear the dependence of the cell performance on its operating conditions. Up to now, the authors have already developed the simulation codes for the one channel region and the single cell plate in its cell stack. To calculate accurately the effect of radiation heat transfer from the cell stack surfaces, however, a code that can treat the whole cell stack is necessary. In the present study, therefore, the authors newly develop a three dimensional simulation code of the planar SOFC stack, and the detailed effect of the radiation heat transfer is investigated. It is made clear that the conventional codes are sufficiently accurate, and the newly developed whole cell stack code is not inevitable to predict the maximum cell temperature. This is because the thermal conductivity of the cell materials made of ceramics is very small, and the central part of the cell stack is almost free from the influence of radiation heat transfer. On the other hand, the stack simulation is needed to calculate accurately the cell voltage because the radiation heat transfer reduces it when the ambient temperature is low. The bad influence of low ambient temperature on the voltage is, however, small and relatively high voltage is obtained even when the ambient temperature is very low. [Copyright &y& Elsevier]

Abstract: The solid oxide fuel cell (SOFC) has a problem in durability of the ceramics used as its cell materials because its operating temperature is very high and the cell temperature fluctuation induces thermal stress in the ceramics. The cell temperature distribution in the SOFC, therefore, should be kept as constant as possible during variable load operation through control of the average current density in the cell. Considering this fact, the authors numerically optimize the operating parameters of air utilization and the inlet gas temperature of the planar SOFC by minimizing the cell temperature shift from its nominal value and propose a new cell temperature control method that adopts these optimum operating parameters for each average current density. The effectiveness of the proposed method is very high and the temperature variation is suppressed to a very low level without lowering the single cell voltage for both the co-flow and counter-flow type cells, indicating that the proposed cell temperature control method makes variable load operation of the planar SOFC possible. [Copyright &y& Elsevier]

Abstract: The authors investigate in detail the influence of the mixing ratio of hydrogen and carbon monoxide in the fuel on the cell performance of the SOFC through numerical simulations for a single cell plate of the co-flow type planar cell. It is made clear that the cell performance is almost the same and excellent, independent of the mixing ratio of hydrogen and carbon monoxide under the nominal operating condition. The electromotive force of the hydrogen rich fuel gas is a little higher than that of the carbon monoxide rich fuel gas. The internal voltage drop in the cell decreases as the fraction of carbon monoxide becomes high. Since the value of the single cell voltage is determined by the balance of these two phenomena, the lowering of the electromotive force is dominant and the single cell voltage of the hydrogen rich fuel gas is higher when the inlet gas temperature is high, whereas the voltage drop reduction is dominant and the single cell voltage of the carbon monoxide rich fuel gas is higher when the temperature is low. The effect of the additional gases of water vapor and carbon dioxide is restricted to the single cell voltage shift, and the qualitative dependence of the single cell voltage on the inlet gas temperature is determined by the mixing ratio of hydrogen and carbon monoxide. [Copyright &y& Elsevier]

Abstract: The authors newly propose and investigate two types of carbon dioxide recovering SOFC/GT combined power generation systems in which a gas turbine with carbon dioxide recycle or water vapor injection is adopted as the bottoming cycle. In these systems, fuel gas is first introduced to a SOFC, and its exhaust fuel gas is afterburned by pure oxygen. Carbon dioxide or water vapor is also injected into the combustor to reduce the combustion gas temperature. The obtained combustion gas, which is composed of only carbon dioxide and water vapor, is introduced to a gas turbine in the bottoming cycle. The exhaust gas of the gas turbine preheats the injection gas, and then, carbon dioxide is separated by only cooling and water condensation. It is made clear that the overall efficiency of the system with carbon dioxide recycle reaches 63.87% (HHV) or 70.88% (LHV), and that of the system with water vapor injection reaches 65.00% (HHV) or 72.13% (LHV). These values are sufficiently high, indicating that the proposed systems are worth further research and development. [Copyright &y& Elsevier]

The authors conduct detailed r–z two dimensional time dependent numerical simulations of a closed cycle disk MHD generator for various load conditions. The objective of this study is to compare the results of the newly performed detailed r–z two dimensional time dependent numerical simulations with those of the already performed quasi-one dimensional time dependent numerical simulations. In the calculations, the generator using cesium seeded helium plasma with 100 MW thermal input and 40 MW electrical output is assumed, and the extent from its subsonic nozzle to diffuser is considered as the analytical region. It is made clear that the two dimensional simulation results almost coincide with the quasi-one dimensional ones except for the high load resistance condition. The intermittent discharge phenomenon under high load resistance condition is simulated for the first time in the present study. This means that the quasi-one dimensional simulations are unreliable when the load resistance is high, indicating the necessity of the present simulations. [Copyright &y& Elsevier]

The authors suppose an interconnecting system between a commercial scale closed cycle MHD combined generation plant and power grid, in which a disk MHD generator using cesium seeded helium plasma and a synchronous generator are connected in parallel to an infinite bus through a common power transmission line, and perform detailed numerical simulations of the transient behavior of the whole system. It is made clear that the transient stability of the closed cycle disk MHD generator using cesium seeded helium plasma is excellent under the power line fault condition, even in the case where the generator is commercial scale and is connected to the power grid in parallel with a synchronous generator. It is also made clear that the effectiveness of the control method for power system stabilization using the fast power control of the MHD generator recently proposed by the authors is sufficient in the case where the working plasma of the MHD generator is cesium seeded helium because the transient stability of the MHD generator is always maintained and the transient rotor angle swing of the synchronous generator is notably suppressed. [Copyright &y& Elsevier]

The authors propose and investigate a new improvement method for transient stability under power line fault condition for commercial scale open cycle subsonic inflow disk MHD generators connected to the power system through time dependent numerical simulations of a total interconnecting system. The method needs no additional device and only manipulates the inverter control angle. Its control sequence has two steps. At first, the control angle is reduced toward 90° just after the fault occurs. Next, it is linearly increased to its rated value with constant increasing rate per cycle after the removed line is reconnected. It is made clear through the simulations that the proposed control scheme of the inverter is very effective to improve the transient stability of the generator. The reduction of the inverter control angle is effective to stabilize the MHD generator, but the operating state shifts from its normal operation. The increase of the control angle can stably return the generator to its normal operation. [Copyright &y& Elsevier]

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. A solid oxide fuel cell (SOFC) is selected as the topping cycle. The exhaust fuel gas of the SOFC is afterburned with its exhaust oxidant gas of pure oxygen, and the heat of the combustion gas is utilized in the bottoming cycle. A closed cycle 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 the energy balance that the total thermal efficiency of the system using natural gas (methane) as the fuel reaches 63.66% (HHV) or 70.64% (LHV). This efficiency is very high for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance and is worth further research and development. [ABSTRACT FROM AUTHOR]

A power inversion and control system for a supersonic closed cycle disk MHD generator, using a current source PWM inverter, is considered, and its performance is confirmed through numerical simulations for a model system in which the MHD generator with 100 MW thermal input and 40 MW electrical output, using cesium seeded helium plasma, is connected to the electric power system, expressed by the infinite bus, via the power inversion and control system and the power transmission line. It is made clear that the system can stably and steadily transmit the nominal electric power from the MHD generator to the electric power system under the nominal operating condition. The system is robust for the change of the a.c. side voltage, and the nominal operation of the MHD generator can be kept, even in the case of voltage fluctuation. It is also made clear that the active and reactive power provided to the electric power system stably and steadily trace the change of their set values, indicating the excellent power control performance of the system. [Copyright &y& Elsevier]

The authors developed a simulation program for a single cell of industrial-sized planar solid oxide fuel cell (SOFC) with a scandia-ceria-stabilized-zirconia (10Sc1CeSZ) electrolyte fed with hydrogen fuel gas, to investigate its operating characteristics under fuel gas leakage conditions. Firstly, the numerical and corresponding experimental results were compared under conditions with no fuel gas leakage. The results confirmed the sufficient validity of the developed simulation program. Next, using the program, simulations involving fuel gas leakage on both sides of the SOFC were carried out. It was found that fuel gas leakage alters the stream of the fuel gas and induces a serious shortage of fuel gas in the downstream area of both side channels. This leads to a significant reduction in the local electromotive force and the appearance of regions where local electrolysis of water vapor occurs, in the downstream area on both sides. The effect of fuel gas leakage on the single cell voltage and the differential resistance was also investigated. It was revealed that the fuel gas leakage cannot be detected by only measuring the single cell voltage. On the other hand, the fuel gas leakage can be detected at an early stage, when only several percent of its inlet flow rate leaks, by measuring the differential resistance under a high fuel utilization rate condition of about 90 % and above. Based on this result, the authors proposed to employ the differential resistance, instead of the single cell voltage, as an evaluation index to detect the fuel gas leakage. [ABSTRACT FROM AUTHOR]

Highlights • A novel degradation diagnosis method for photovoltaic modules was proposed. • The proposed method utilizes xenon flash lighting system and detector capacitor. • The proposed method includes sensing process of module temperature. • The proposed method can evaluate increase of module internal series resistance. • The proposed method can find out modules with broken bypass diode. Abstract This paper proposes a novel and unique degradation diagnosis method for photovoltaic modules employing a xenon flash lighting system and a capacitor for degradation detection connected to the module output. The xenon flash lighting system is not only compact and lightweight but also small in power consumption and can be lit by batteries. Therefore, the portability of the lighting system is satisfactory, and the proposed diagnosis method is expected to be relatively easily applicable to outdoor photovoltaic power plants. In addition, since the lighting system can provide artificial and precisely controlled intense flash light to the module and this proposed method includes a sensing process of the module temperature, this proposed method can, in principle, evaluate the internal series resistance and determine accurate degradation level independent of the weather and temperature conditions. The authors carried out the numerical simulations and successfully made clear that the theoretically unavoidable measurement error of the internal series resistance is only 2% less than its variation width, confirming the validity of the basic ideas of the proposed degradation diagnosis method. The authors then performed the demonstration test experiments using a prototype experimental apparatus and investigated its practicability for real PV modules, successfully confirming that the same accuracy as expected through the simulations can be achieved also through the experiments. [ABSTRACT FROM AUTHOR]

Energetic feasibility analyses were conducted when an SOFC CGS with EV charging equipment is installed in a facility with a high hot-water demand and a high thermo-electric demand ratio. The university cafeteria located on the Hitachi Campus of Ibaraki University in Japan was selected as an installation target because its electric and hot-water demands fulfilled the intended criterion of a high thermo-electric demand ratio. It was made clear that the merits of a co-generation system are not optimal in the case a gas water heater is selected as the backup hot-water supply. To solve the problems contributing to this bad result and to improve the performance, the authors next selected a heat pump water heater as the backup hot-water supply. It was made clear that this system possesses sufficiently high energy savings performance. It was also shown that the coexistence and co-prosperity of the cafeteria and EV charging equipment are successfully achieved. These results reveal that an SOFC CGS with EV charging equipment can be a feasible candidate for a future energy supply system installed in Japanese cafeteria, which is a facility with a large hot-water demand and a high thermo-electric demand ratio, by adopting a heat pump water heater, instead of the usual gas water heater, as the backup hot-water supply. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical simulation method to calculate transient voltage profiles of lithium-ion secondary batteries. The method employs circuit analysis of an internal equivalent electric circuit composed of an electromotive force, an LR parallel circuit, and eight CR parallel circuits. To demonstrate the accuracy and versatility of this approach, the authors measured the transient voltage responses of three types of test batteries with different output power densities, and compared these experimental data with simulation results. Battery performance was tested using different charge/discharge current patterns and a range of values for state of charge (SOC) and operating temperature. The accuracy of the proposed simulation method was confirmed for all test cases using the three different batteries and charge/discharge current patterns, demonstrating that the method is versatile and applicable to various lithium-ion secondary batteries regardless of type. Since the employed internal equivalent electric circuit is composed of only DC voltage source and linear R , L and C elements, all of general purpose software for electric circuit simulations can easily deal with the circuit. This advantage and the obtained results indicate that the proposed simulation method is a useful technique and offers a powerful tool to develop sophisticated battery control systems for various applications. [ABSTRACT FROM AUTHOR]

Abstract: The authors propose a solid oxide fuel cell (SOFC) co-generation system integrated with an electric vehicle (EV) charging station. To examine the feasibility of the proposed system, the authors numerically simulated the operation pattern of the proposed system, using the electric and thermal demands measured at a multifamily apartment from May 2003 to April 2004. Based on the simulation results, the authors calculated the overall efficiency of the system as well as the primary energy saving rate. The available electric energy for EV charging was also evaluated for the case of the proposed system installed in the multifamily apartment. As a result, it is made clear that the annually averaged overall efficiency reaches about 77% (LHV) and the expected primary energy saving rate exceeds 30% throughout the year. In addition, it is also found that sufficient amount of electric energy for EV charging can be obtained from the proposed system. Therefore, it can be concluded that the proposed SOFC system can successfully combine electrical/thermal energy co-generation and electric vehicle charging while maintaining high energy efficiency and good matching to energy consumption patterns. [Copyright &y& Elsevier]