Fuel Cell System Control

4 Control System 12.4.1 Fuel Cell System Control 

A fuel cell system may be well understood, but it requires a control strategy for predictable operation. Fuel cell systems are complex and must have some sort of regulation to reliably achieve desired power levels. Without regulation, fuel cell power output will drift over time, even if reactant flow rates 

Neural networks and fuzzy logic have also been applied in the development of the control system of the fuel cell. 

---

The fuel cell system is controlled by a so called fuel cell control unit (FCU) in which all the algorithms are implemented. The fuel cell system controller communicates with the vehicle controller via a CAN interface and controls aU the high dynamic processes to feed the proper amount of hydrogen and air. In additimi the FCU controls all the processes like for example the start-up and the shut-down procedure and the overall water management. 

Water balance and management are an important concern in PEM fuel cell system control. Dynamic water balance and management have become one of the major technical challenges for PEM fuel cell design and operation because they have a direct influence on the performance and lifetime of PEM fuel cell systems. 

High Temperature PEM Fuel Cell Systems, Control and Diagnostics... 

Assuming a theoretical efficiency of the fuel-cell system of around 60% and an electric-drive-train efficiency of 90%, the overall fuel-cell system efficiency is about 55%. The theoretical efficiencies for a fuel cell cannot be realised in practice. The efficiency of the system (including fuel treatment, air supply and others) is already lower than that of the pure fuel-cell stack on its own the overall efficiency of the FC drive train falls to less than 40% as a result of additional components, such as compressors, control electronics and others, see Fig. 13.6. 

A similar study was performed by Jian-hua et al. [137], who used (NH4)2S04 as the pore former due to its high solubility in water. After fuel cell testing was performed, it was observed that the pore former improved the performance of the cell at higher current densities (>0.9 A cm" ), indicating that control of the pore distribution in the MPL and DL was critical to enhancing the efficiency of the fuel cell system. 

Apart from hydrocarbons and gasoline, other possible fuels include hydrazine, ammonia, and methanol, to mention just a few. Fuel cells powered by direct conversion of liquid methanol have promise as a possible alternative to batteries for portable electronic devices (cf. below). These considerations already indicate that fuel cells are not stand-alone devices, but need many supporting accessories, which consume current produced by the cell and thus lower the overall electrical efficiencies. The schematic of the major components of a so-called fuel cell system is shown in Figure 22. Fuel cell systems require sophisticated control systems to provide accurate metering of the fuel and air and to exhaust the reaction products. Important operational factors include stoichiometry of the reactants, pressure balance across the separator membrane, and freedom from impurities that shorten life (i.e., poison the catalysts). Depending on the application, a power-conditioning unit may be added to convert the direct current from the fuel cell into alternating current. 

There have been few synthetic reports employing these monomers beyond the Ballard work, most likely as a result of presumed high cost and monomer availability. However, the performance and stability demonstrated by these materials in fuel cells may spur further developments in this area. The above-reported copolymers are believed to be random systems both in the chemical composition of the copolymer backbone and with regard to sulfonic acid attachment. Novel methods have been developed for the controlled polymerization of styrene-based monomers to form block copolymers. If one could create block systems with trifluorostyrene monomers, new morphologies and PEM properties with adequate stability in fuel cell systems might be possible, but the mechanical behavior would need to be demonstrated. 

Conventional fuel cell systems provide the designer with greater control over operating conditions as compared to the implantable and ambient-fuel categories. For example, the pH of the system can be adjusted well above or below neutral, and the opportunity exists to eradicate all poison species from the system. As previously mentioned, the realm of... 

Development of PEM stack and components (1-5 kW). Activity cost 0.6 million. Partner Arcotronics Fuel Cells. Construction of a 1 kW stack with novel solutions and low cost development of a fuel processing system. Partner ENEA, Arcotronics Fuel Cells, Research Institutions. Systems development of key components (fuel processing systems, controlling systems, auxiliaries) construction of prototypes and testing. Budget 2.88 million. Partners ENEA, Arcotronics Fuel Cells, Universities and CNR. 

The critical technology development areas are advanced materials, manufacturing techniques, and other advancements that will lower costs, increase durability, and improve reliability and performance for all fuel cell systems and applications. These activities need to address not only core fuel cell stack issues but also balance of plant (BOP) subsystems such as fuel processors hydrogen production, delivery, and storage power electronics sensors and controls air handling equipment and heat exchangers. Research and development areas include ... 

Sensor and control technology with the proper ranges and selectivities for integrated fuel cell system application. 

Cominos, V., Hofmann, C., State-of-the-art fuel cell systems for portable devices and the applicability of the MiRTH-e system, Control No. ENK6-CT-2000-00110, funded by the European Comission,... 

The operation of fuel cells has already been described in Section 1.3.5 (Chapter 1). Here, the emphasis will be on the control of these devices. Further research is required to reduce the cost of instruments for all fuel cell systems. For example, a complex fuel cell system can require upward of 100 flow control valves. Even if the cost is only 200 for a typical low-cost commercial valve, this cost can exceed the total cost of alternative electricity generation components by a sizable margin. Transition to high-temperature fuel cells pushes the valve price up as special materials are required, yet low cost is critical for commercial viability and salability of fuel cells if they are ever to move out of the laboratory and into general use. 

---