Danish Power Systems (Denmark)

In recent years, it has become increasingly important to rely less on conventional fossil fuels for energy generation and shift towards greener alternatives like solar and wind. As the world adopts such green technologies, a problem arises due to their intermittent and varied supply of energy. An obvious solution is to utilize energy storage technologies; among the various candidates, fuel cells for grid level energy storage have emerged as a promising and efficient technology.Solid oxide cells (SOCs) are a cost effective and highly efficient technology for energy storage using hydrogen and are typically manufactured from abundantly available resources. A prominent advantage of SOCs over other fuel cell technologies is their reversibility; i.e., they can be run in either fuel cell (SOFC) or electrolysis (SOEC) mode for generating electricity or fuel according to needs. A typical SOC consists of a porous substrate, with an anode (fuel electrode) on top. On the other side, a thin layer of porous cathode (air electrode) is present, and the anode and cathode sides are separated by a thin, dense electrolyte layer which is ionically conductive. The anode and cathode also need to be both ionically and electronically conductive. SOCs are being developed and optimized with the aim of minimizing or eliminating any deficiencies.One such deficiency arises in the manufacturing of the substrate for SOCs, which typically consists of nickel oxide (NiO) and yttria stabilized zirconia (YSZ), which are ceramics, requiring high temperatures (>1350˚C) for sintering to achieve appropriate mechanical strength and porosity. NiO is reduced after fabrication to Ni, which provides catalytic activity for hydrogen oxidation or reduction. The high sintering temperature increases the cost of manufacturing, as more power is required and a higher grade refractory is required in the furnace. This is not feasible for large-scale production. High sintering temperatures can also promote the formation of undesirable zirconate phases, which degrade the performance.The sintering temperature for the substrate depends on its morphology, such as the particle size and surface area of the powders that are used to manufacture the substrate. Modifying these parameters can have a major effect on cell performance, since the porosity necessary for gas diffusion is affected, as are percolation of the ionic and electronic conductive pathways and the mechanical integrity of the cell. This study is targeted towards reducing the sintering temperature for the half cell, which consists of the substrate, anode (fuel side electrode), and electrolyte, with the aim of achieving comparable cell performance to cells obtained by sintering at higher temperatures. Cells using NiO and YSZ powders with different particle sizes and surface areas are fabricated and their sintering behaviour is assessed for the desired temperature range. The powder particle sizes are also tailored using high energy ball milling, such as attrition milling, for various times to change the particle size ratio. The cells are then tested for their electrochemical and mechanical performance. Preliminary results indicate a clear trend, whereby there is a reduction in the sintering temperature as the NiO particle size is reduced without changing the YSZ powder size. Sintering temperatures as low as 1250˚C have been achieved when high surface area YSZ particles are used with fine, ball milled NiO powder.

Industrial facility with large islanded 13.8kV electrical system consists of existing four gas powered turbine generators connected to main switchgear line-up. Outgoing 13.8kV feeders to various facility loads are 13.8kV cables of various sizes ranging from #2 AWG to 750 MCM with total cable network length of approximately 28 miles. Since all existing generators and the new planned generator are 5/6 winding pole pitch, zero-sequence triplen (3rd, 9th, 15th, etc) harmonic currents are expected to circulate between all connected generators through the closed loop of the main switchgear bus and also between all generators and the equivalent system cable capacitance to ground.This paper investigate the impact of 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic circulating currents between all generators and the system cable's capacitance to ground on system performance and ground fault protection schemes. This study is limited to the 13.8kV system as most facility loads are fed from area transformers with delta/wye windings that isolate its zero-sequence loop from the main 13.8kV system.This investigation discovered significant 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic circulating currents in the existing system and the new planned generator is expected to make this problem worse. Therefore, system grounding resistors is upgraded to non-standard units to withstand increased steady state 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic circulating currents. Ground fault protection adjustments was found to be necessary to prevent nuisance and sympathetic trips.

In this paper, a simple and accurate method is proposed for online estimation of the rotor permanent magnet (PM) flux linkage for surface mounted PM synchronous machines. By advantageously utilizing an injected zero-voltage vector, the effects of inductance in estimating the PM flux linkage is eliminated. The inverter voltage error and phase resistive voltage drop effects are minimized by repeating the test at different speeds. Therefore, as a result, only the voltage commands are needed for PM flux linkage estimation, resulting in great simplicity. Filtering the current ripple caused by the zero-voltage vector injection is not necessary. The proposed method can be used with sensored or sensorless field-oriented control strategies. The experimental results have shown a good accuracy of the proposed new method.

Power electronics technology has been widely used for decades in the modern motor drive systems. Beyond the control flexibility, the power electronics devices (e.g., diode rectifiers) are also the main harmonic source to the grid due to their nonlinearity, which deteriorate the power grid quality and may cause unnecessary losses in power system transformers. Both degradations are apt to occur in motor drive applications. As a consequence, it calls for advanced and intelligent control strategies for the power electronics based drive systems like adjustable speed drives in industry. At present, many industrial drives are still equipped with three-phase diode rectifiers. Thus, it is difficult to implement the prior-art harmonic control strategies for active front-ends. Moreover, the total cost and complexity has become an obstacle for these harmonic elimination approaches in multiple drive systems. Therefore, in this paper, a new cost-effective harmonic mitigation approach has been proposed for multiple drives. The proposed approach can control the generated current harmonics by benefiting of the nonlinearity of the drive units and through a novel current modulation scheme. Simulation and experimental results have validated the effectiveness of the proposed approach in terms of harmonic elimination in three-phase multi-drive systems.

Several years ago, the answer to this question was negative based on the criteria for an anode with <0.1 mg cm-2 of platinum group metals to perform similarly without and with 50 ppm CO in hydrogen proton exchange membrane fuel cells (PEMFCs). Now, with the amount of CO impurities reduced to 10 ppm in reformates, a <1% performance loss with a 1.5% air-bleed has become a reasonable target. The CO-tolerant catalyst also needs to be dissolution resistant up to 0.93 V, viz., the potential experienced at the anode during startup and shutdown of the fuel cells. We recently demonstrated our ability to simultaneously enhance activity and stability by using single crystalline Ru@Pt core-shell nanocatalysts. Here, we report that the performance target with reformates was met using bilayer-thick Ru@Pt core-shell nanocatalysts with 0.047 mg cm-2 Pt and 0.024 mg cm-2 Ru loading, supporting a positive prognosis for the economically viable use of reformates in PEMFC applications.

The lifetime of proton exchange membrane (PEM) fuel cells depends largely on the durability of the PEM and is a critical issue in the commercialization of PEM fuel cell technology (1, 2). Perfluorosulfonated acid (PFSA) membranes, such as Nafion®, are the most widely used electrolyte material for PEM fuel cells.Many factors can cause PEM failure, including manufacturing and design issues, material properties, and fuel cell operation conditions. Each factor results in failure through a particular degradation mode. These modes can be classified as thermal, mechanical, and chemical modes (3-7). Because fuel cells typically operate at temperatures below that at which Nafion thermally degrades, chemical and mechanical degradation are generally considered the most important modes of membrane degradation.Although there has been a lot of progress in the area, the exact chemical membrane degradation mechanisms, the most susceptible points, and the impact of test conditions on degradation are not completely understood. The formation of radicals and their reactivity during the fuel cell operation have been confirmed as the main cause of PEM chemical degradation (8-11). These radicals are formed as a result of the reaction of crossover H2 and O2 on the surface of Pt or other metal ion contaminants (4). In addition to the electrodes, Pt particles have been observed to migrate into the membrane, producing another site for radical formation. Radical attack leads to loss of fluorine, sulfur, and organofluorine compounds from the PEM, and PEM thinning, all resulting in loss of mechanical integrity. The radical formation mechanisms and the impact of test conditions on radical formation are also not completely understood.It has been suggested that earlier versions of Nafion membranes chemically degrade through radical attack on carboxylic acid groups end groups (12-14) or at the C−S or O−C bonds in the side chain and main chain (12, 14-18), as shown in Figure 1. Chemically stabilized Nafion, e.g., Nafion 211, has been developed where the concentration of terminal carboxylic acid groups was decreased to negligible levels and, as a result, degradation decreased substantially (13). The use of radical scavengers such as ceria have increased the durability of PFSA membranes by as much as 1000-fold compared to unmitigated membranes (19). Despite the recent durability improvements, there is evidence that PFSA membranes are still susceptible to chemical damage.Typical indicators for chemical degradation of Nafion membranes include increased H2crossover, decreased ion exchange capacity, decreased proton conductivity, and decreased PEM thickness. Localized crossover tests have shown that membrane damage occurs preferably at the perimeter of the active area. The quantitative method of choice used for detecting chemical degradation is typically detection of fluoride in fuel cell outlets, reported as a fluoride emission rate (FER).Figure 1. Proposed locations of radical attack in NafionTo improve PEM chemical durability, a true understanding of the decay mechanisms is required. Models of some of the decay modes have been developed and they show a consistent but incomplete understanding of membrane decay. Through a combination of specific modeling and directed testing, an overall decay model can be developed.

FuelCell Energy is developing a Hybrid Solid Oxide Fuel Cell (SOFC)-Battery Energy System for Large Displacement Unmanned Undersea Vehicle (LDUUV) propulsion as part of the Office of Naval Research’s LDUUV Innovative Naval Prototype (INP) Energy Program. The project objective is the development of an air-independent refuelable power system with high energy density suitable for long duration underwater missions. The Hybrid SOFC-Battery system will be capable of generating 1800kWhr of electricity over a 70 day mission with no exhaust discharged outside of the vehicle at any time. The energy system is fueled by JP-10 logistic fuel, utilizes liquid O2 for air-independent operation, and is compact enough to fit within a 42-inch square by 120-inch long LDUUV power section. Phase I of the project includes process design and cost analysis, development of a 3-D CAD model of the energy system, breadboard testing of components and the integrated system, as well as completion of a Preliminary Hazard Analysis (PHA).

High Temperature Polymer Electrolyte Membrane (HT-PEM) Fuel Cells provide an attractive alternative to Low Temperature PEM fuel cells with respect to fuel flexibility, simplified cooling system, balance of plant and higher value waste heat without reactant humidification. Optimization of the PEM is critical to achievement of these performance benefits and PEMs derived from phosphoric acid-doped polybenzimidazoles (PBIs) are the most successful for high temperature operation. However, PBI-based membranes face a number of challenges, including oxidative stability and durability in a fuel cell. In this work we present single-cell fuel cell performance using m-PBI membranes with hydrogen.

Testing of a 300 W stack, supplied by Versa Power Systems Ltd., and a sodium - metal chloride (ZEBRA) battery has been performed with a view to assessing the feasibility of combining an intermediate temperature solid oxide fuel cell with a high temperature battery for automotive traction applications. Field testing of a self-compressed stack is demonstrated including consideration of the mechanical robustness of the technology. The battery system, comprising novel cell technology, is tested under pulse discharge and standard driving cycle conditions. Based on modeling studies previously performed, the performance results obtained and the reliability of the respective technologies, development of a full-scale prototype is considered viable and ultimately commercially relevant.