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While the integration of base-load fuel cells into the built environment is expected to provide numerous benefits to the user, the steady-state and dynamic behavior of these stationary fuel cell systems can produce an undesirable impact on the grid distribution circuit at the point of connection. In the present paper, a load-following active power filter (LFAPF) is proposed to mitigate the grid impact of such systems and instead improve overall local power quality. To evaluate the strategy, the LFAPF is integrated into a SOFC system inverter with one-cycle control (OCC) to provide the fundamental benefits of a traditional active power filter (APF) while also damping out short-term line current transients. The LFAPF benefit is illustrated through simulation of an SOFC interconnected with the utility electric distribution system and a building electricity demand that is modeled as a dynamic non-linear load. Three installation cases are examined: (1) a load-following SOFC, (2) a base-loaded SOFC, and (3) an offline SOFC. Without LFAPF, the load-following SOFC causes load transients due to the finite SOFC response time, and the base-loaded SOFC case has transients that appear more severe because they represent a larger overall percentage of the grid-provided load. The integration of an LFAPF improves the steady-state behavior over the base case and mitigates voltage sags and step changes. Thus integrating an LFAPF can, by providing useful services to both the utility and the end-user, facilitate the integration of an SOFC into the distribution system. © 2009 Elsevier B.V. All rights reserved.

Fuel Cell/Gas Turbine (FC/GT) hybrid technology is promising, but introduces challenges in system operation and control. For base-load applications, changes in ambient conditions perturb the system and it becomes difficult to maintain constant power production by the FC/GT system. If the FC/GT hybrid system is load-following, then the problem becomes even more complex. In the current study, a dynamic model of a FC/GT power plant is developed with system controls. Two cases are evaluated: (1) system controls are developed to maintain constant power and process control within acceptable constraints and (2) the FC/GT power plant is set in power following mode connected in parallel to the grid for a daily load profile scenario. Changing ambient conditions are employed in the dynamic analysis for both cases. With appropriate attention to design of the system itself and the control logic, the challenges for dynamic system operation and control can be addressed. © 2010 by ASME.

Proper converter design can allow solid oxide fuel cells operated as distributed generators to mutually benefit both the load and the electric utility during steady-state conditions, but dynamic load variations still present challenges. Unlike standard synchronous generators, fuel cells lack rotating inertia and their output power ramp rate is limited by design. Two strategies are herein investigated to mitigate the impact of a large load perturbation on the electric utility grid: 1) external use of ultracapacitor electrical storage connected through a dc-dc converter and 2) internal reduction of steady-state fuel utilization in the fuel cell to enable faster response to output power perturbations. Both strategies successfully eliminate the impact of a load perturbation on the utility grid. The external ultracapacitor strategy requires more capital investment while the internal fuel utilization strategy requires higher fuel use. This success implies that there is substantial flexibility for designing load-following fuel cell systems that are model citizens. © 2009 IEEE.

Adding distributed generation (DG) is a desirable strategy for providing highly efficient and environmentally benign services for electric power, heating, and cooling. The interface between a solid oxide fuel cell (SOFC), typical loads, and the electrical grid is simulated in Matlab/Simulink and analyzed to assess the interactions between DG and the electrical grid. A commercial building load profile is measured during both steady-state and transient conditions. The load data are combined with the following models that are designed to account for physical features: a One-Cycle Control grid-connected inverter, a One-Cycle Control active power filter, an SOFC, and capacitor storage. High penetration of DG without any power filter increases the percentage of undesirable harmonics provided by the grid, but combined use of an inverter and active power filter allows the DG system interconnection to improve the grid tie-line flow by lowering total harmonic distortion and increasing the power factor to unity. © 2008 Elsevier B.V. All rights reserved.

The implementation of Distributed Generation (DG) may lead to increased pollutant emissions that adversely affect air quality. This work presents a systematic methodology to characterise DG installation in urban basins. First, a set of parameters that characterise a DG implementation scenario is described. Second, a general approach using Geographic Information Systems (GIS) data is presented. Third, the methodology is demonstrated by application to the South Coast Air Basin (SoCAB) of California. Results show that realistic scenarios in the SoCAB concentrate DG technologies nearby industrial zones and introduce pollutant mass increments no larger than 0.43% with respect to baseline emissions. © 2008 Inderscience Enterprises Ltd.

Implementing environmentally friendly fuels and high efficiency propulsion technologies to replace the Internal Combustion Engine (ICE) fueled by fossil fuels such as Heavy Fuel Oil (HFO) and Marine Gas Oil (MGO) on board ships represents an attractive solution for maritime power. In this context, fuel cells can play a crucial role, thanks to their high energy efficiency and ultra-low to zero criteria pollutant emissions and environmental impact. This paper performs the technical feasibility analysis for replacing the conventional diesel engine powertrain on board a commercial vessel with an innovative system consisting of ammonia-fuel-based Solid Oxide Fuel Cell (SOFC) technology. Taking into account the size of the diesel engines installed on board and the typical cruise performed by the commercial vessel, the ammonia consumption, as well as the optimal size of the innovative propulsion system have been assessed. In particular, the SOFC powertrain is sized at the same maximum power output as the main reference diesel engine. The mass and energy balances of the ammonia-based SOFC system have been performed in Aspen PlusTM environment. The gravimetric (kWh kg−1) and volumetric (kWh m−3) energy density features of the ammonia storage technology as well as the weight and volume of the proposed propulsion system are evaluated for verifying the compliance with the ship’s weight and space requirements. Results highlight that the proposed propulsion system involves an increase in weight both in the engine room and in the fuel room compared to the diesel engine and fuel. In particular, a cargo reduction of about 2.88% is necessary to fit the ammonia-based SOFC system compared to the space available in the reference diesel-fueled ship.

This paper analyzes and compares transient and steady-state performance characteristics of different types of single-shaft turbo-machinery for controlling the air through a pressurized solid oxide fuel cell (SOFC) stack that is integrated into a SOFC/GT pressurized hybrid system. Analyses are focused on the bottoming part of the cycle, where the gas turbine (GT) has the role of properly managing airfiow to the SOFC stack for various loads and at different ambient conditions. Analyses were accomplished using two disparate computer programs, which each modeled a similar SOFC/GT cycle using identical generic gas turbine performance maps. The models are shown to provide consistent results, and they are used to assess: (1) the influence of SOFC exhaust composition on expander behavior for on-design conditions, (2) the off-design performance of the bypass, bleed, and variable speed controls for various part-load conditions and for different ambient conditions; (3) the features of such controls during abrupt transients such as load trip and bypass/bleed valve failure. The results show that a variable speed micro-turbine is the best option for off-design operation of a SOFC/GT hybrid system. For safety measures a bleed valve provides adequate control of the system during load trip. General specifications for a radial GT engine for integration with a 550 kW pressurized SOFC stack are identified, which allow operation under a wide range of ambient conditions as well as several different cycle configurations. Copyright © 2007 by ASME.

A novel test protocol is proposed for fuel cells that are in a nonfunctioning or passive state. Standard fuel-cell test methods are reviewed, along with the equivalent circuit models (ECMs) used to represent functioning or active fuel cells. Standard active tests focus on single cells, while the passive test is shown to be applicable to testing multiple cells. The passive test measures electrical characteristics of the fuel cell in the absence of electrochemical reactions. A simple ECM is developed to describe the cell behavior under the passive test conditions. Circuit model parameters of many series-connected cells can be acquired using the results of a single stack test. Proton exchange membrane fuel cells (PEMFCs) from three manufacturers were tested, ranging in system power from 12-500 W. Test results for each PEMFC exhibited similar behavior that is well predicted by the ECM. A strong similarity between a passive fuel cell and a double layer capacitor is discussed. © 2007 IEEE.

Electrocatalytic properties of the interfaces between La 0 8Sr0 2Ga0 8Mg0 115Co 0 085O3-δ (LSGMC) electrolyte and various cathodes: comprised of Sm0 5Sr0 5CoO3-δ (SSC), and La0 7Sr0 3Co0 2Fe0 8O 3-δ (LSCF) in composite forms (70wt.%) with LSGMC (30wt.%) were investigated under both oxygen reduction and evolution conditions. All the oxides were synthesized using the glycine-nitrate process (GNP). Symmetrical electrochemical cells were investigated with three-electrode linear dc polarization and ac impedance spectroscopy. For the composite SSC-LSGMC cathode/LSGMC interface, the cathodic overpotential under 1 A/cm2 current density was as low as 0.085 V at 700°C, 0.062V at 750°C and 0.051V at 800°C in air. Composite LSCF-LSGMC cathode/LSGMC interfaces were found to have about twice the exchange current density of composite SSC-LSGMC/LSGMC interfaces at 700°C © The Electrochemical Society.

A first principles dynamic model of the physical, chemical, and electrochemical processes at work in a proton exchange membrane fuel cell has been developed. The model solves the dynamic equations that govern the physics, chemistry and electrochemistry for time scales greater than about 10 ms. The dynamic equations are solved for a typical but simplified quasi-three dimensional geometric representation of a single cell repeat unit of a fuel cell stack. The current approach captures spatial and temporal variations in the important physics of heat transfer and water transport in a manner that is simple enough to make the model amenable to PEMFC system simulations and controls development. Comparisons of model results to experimental data indicate that the model can well predict steady state voltage-current relationships as well as the oxygen, water, and nitrogen spatial distribution within the fuel cell. In addition, the model gives dynamic insight into the distribution of current, water flux, species mole fractions, and temperatures within the fuel cell. Finally, a control system test is demonstrated using the simplified dynamic model. © 2006 Elsevier B.V. All rights reserved.

This study is focused on a hybrid fuel cell/gas turbine (FC/GT) system with an atmospheric pressure solid oxide fuel cell (SOFC). The impact of the gas turbine rotational speed on dynamic performance and controllability of a hybrid system is investigated. The transient response of the FC/GT system to perturbations in the power demand has been investigated. Two operational strategies of gas turbines are compared: (1) fixed speed operation, and (2) variable speed operation. For both operation strategies, a wide range of power production is numerically simulated. The results show that variable speed operation is superior for the FC/GT hybrid configuration studied. Variable speed operation allows a 50% turn down in power with no additional balance of plant equipment required. The system efficiency is maintained above 66% for variable speed operation compared to 53% for fixed speed operation with auxiliary combustion. © 2006 Elsevier B.V. All rights reserved.

Solar energy is desirable due to its renewable and pollution-free properties. In order to utilize the present utility grid infrastructure for power transmission and distribution, grid connected dc-to-ac inverters are needed for solar power generation. However, previously proposed voltage source inverters with a two-power-stage structure or a cascaded structure increase the circuit complexity, power losses, and system cost In addition, conventional maximum power point tracking (MPPT) methods usually need power calculation and complex logic judgment, so expensive multipliers and/or microprocessors are needed. This leads to high inverter capital cost, which becomes a major barrier for the wide use of solar power generation. A cost-effective MPPT method integrated within the One-Cycle Control (OCC) core is proposed in this paper. When integrated with a three-phase boost type inverter, the proposed method tracks MPP with good precision, and solar power is converted into three-phase ac power with a single power stage. There is no power calculation in the controller, which yields a simple and cost-effective solution. Experiments have been carried out with a photovoltaic source to verify good performance. © 2006 IEEE.

This paper presents the electricity and hydrogen co-production concept, a methodology for the study of SOFC hydrogen co-production, and simulation results that address the impact of reformer placement in the cycle on system performance. The methodology is based on detailed thermodynamic and electrochemical analyses of the systems. A comparison is made between six specific cycle configurations, which use fuel cell heat to drive hydrogen production in a reformer using both external and internal reforming options. SOFC plant performance has been evaluated on the basis of methane fuel utilization efficiency and each component of the plant has been evaluated on the basis of second law efficiency. The analyses show that in all cases the exergy losses (irreversibilities) in the combustion chamber are the most significant losses in the cycle. Furthermore, for the same power output, the internal reformation option has the higher electrical efficiency and produces more hydrogen per unit of natural gas supplied. Electrical efficiency of the proposed cycles ranges from 41 to 44%, while overall efficiency (based on combined electricity and hydrogen products) ranges from 45 to 80%. The internal reforming case (steam-to-carbon ratio of 3.0) had the highest overall and electrical efficiency (80 and 45% respectively), but lower second law efficiency (61%), indicating potential for cycle improvements. Copyright © 2006 by ASME.

Hybrid fuel cell/gas turbine systems provide an efficient means of producing electricity from fossil fuels with ultra low emissions. However, there are many significant challenges involved in integrating the fuel cell with the gas turbine and other components of this type of system. The fuel cell and the gas turbine must maintain efficient operation and electricity production while protecting equipment during perturbations that may occur when the system is connected to the utility grid or in stand-alone mode. This paper presents recent dynamic simulation results from two laboratories focused on developing tools to aid in the design and dynamic analyses of hybrid fuel cell systems. The simulation results present the response of a carbonate fuel cell/gas turbine, or molten carbonate fuel cell/gas turbine, (MCFC/GT) hybrid system to a load demand perturbation. Initial results suggest that creative control strategies will be needed to ensure a flexible system with wide turndown and robust dynamic operation. Copyright © 2006 by ASME.

Distributed Energy Resources (DER) have the potential to meet a significant portion of increased power demands of the future. DER applications can potentially provide benefits in electrical reliability and power quality, in addition to reducing total energy costs in combined cooling, heating and power (CHP) applications. However, the shift from a central generation paradigm to distributed generation results in different emissions characteristics and profiles from both a spatial and temporal perspective. Distributed generation is characterized by many sparsely distributed stationary sources within an urban air-shed compared to central generation where emissions sources are much larger, but typically located outside the air-shed in more remote locations. As a result, high market adoption of fuel-driven (non-renewable) distributed generation (DG) technologies, such as reciprocating engines and microturbines, may influence the air quality within a region. The present paper estimates air quality impacts for a representative distributed generation scenario in the South Coast Air Basin (SoCAB) of California. Simulations are based on the year 2010 with comparison to a base case scenario with no DG emissions. The DG scenarios are developed for a reasonable percentage of power met by DG, representative spatial distribution and temporal operation, and a mix of DG technologies and emissions factors. The resultant emissions inventory for each DG scenario is then provided as input to a three-dimensional air quality model including detailed atmospheric chemistry and transport for simulation of the SoCAB. Preliminary air quality results suggest that there will be an air quality impact, that the impacts will not be uniform throughout the air-shed, and that individual criteria pollutant concentrations may either rise or fall with the introduction of DG.

This paper proposes a new maximum power point tracking (MPPT) method in combination with One-cycle control for photovoltaic power generation. This control scheme is based on the automatic current-adjusting feature of One-cycle control. The output current of the Inverter can be adjusted according to the voltage of the photovoltaic (PV) array so as to extract the maximum power from it. In the mean time, One-cycle control guarantees that the output current is in the same shape of and in phase with the grid voltage. All these are accomplished in one power stage and a simple control circuit. No detection and calculation of power are needed. Compared with previously proposed approaches, this method Is much more efficient and more cost-effective and yet exhibits excellent performance. The principle is explained qualitatively and extensive experiments have been carried out to verify and validate the proposed method.