Fuel cell system dynamics

There are several fuel cell system dynamic models in the literature that are specifically developed for vehicle propulsion. The simplest dynamic model of a fuel cell stack is the representation of the stack with an equivalent circuit whose operating parameters are based on the polarization curve obtained from the manufacturer data sheet at nominal conditions of temperature and pressure. An equivalent single-cell model with semiempirical equation for the fuel cell polarization curve can also be used for this purpose. 

Safety, Codes and Standards. There are five projects covering different aspects of system challenges when integrating hydrogen technology into an energy system. Important objectives are safety, codes and standards, dynamic behaviour of fuel cell systems, and the evaluation of demonstration projects. 

Traverso A., Trasino F., Magistri F. (2006), Dynamic simulation of the anodic side of an integrated solid oxide fuel cell system. In 8th Biennial ASME Conference on Engineering Systems Design and Analysis, Turin, Italy, ESDA2006-95770. 

Integrated Fuel Cell System Efficiency, Dynamics, Costs... 

Corbo P, Migliardini F, Veneri O (2008) Experimental analysis of a 20 kWe PEM fuel cell system in dynamic conditions representative of automotive applications. Energ Convers Manage 49 2688-2697... 

The control strategies are programmed in Matlab-Simulink, compiled in C-H-and then downloaded into the DSP processor of the d-Space board. The controlled management of the fuel cell system during the dynamic tests operates on hydrogen purge, air flow rate regulation (stoichiometric ratio), external humidification, and stack temperature. 

An important point to consider about the stack management, with reference to an electric power train operating in dynamic conditions, as determined by road requirements, is the regulation of the stack temperature together with the other control parameters of water and reactants to avoid mass transfer limitations and membrane drying out or flooding. Moreover, the interaction between stack and auxiliaries has to be balanced taking into account the optimization of fuel cell system efficiency and reliability (see Sect. 4.6). 

Assess design-point, part-load, and dynamic performance of automotive fuel cell systems and system components. 

Figure 7. Dynamic response of the system on a portion of the FUDS. The fuel cell system s power generation lags behind the driving schedule s power demand during rapid power up-ramps.

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. 

With aid of the inverter, the fuel cell system can supply not only real power but also reactive power. Usually, power factor can be in the range of 0.8-1.0, The SOFC system dynamic model is given in Fig. 14. 

Bischoff, M. (2006) Large stationary fuel cell systems status and dynamic requirements. I. Power Sources, 154 (2), 461-466. 

Bergen, A., Schmeister, T., Pitt, L., Rowe, A., Djilali, N., and Wild, P. (2007) Development of dynamic regenerative fuel cell system. J. Power Sources, 164, 624—630. 

Undesired side reactions occur at high electrode potentials as it is described in Sections 23.3 and 23.4. Long idle phases with cell voltages near OCV should therefore be avoided. This is particularly valid for the upper potential hmit of potential cycles [67], since dynamic operation leads to accelerated cell degradation as explained in Section 20.3. A minimum cell current is required in order to keep the cell voltage significantly lower than OCV. If constant electric consumers are not present in the fuel-cell system, a dummy load can be integrated. 

Adding a battery to a fuel cell electric vehicle has two advantages (i) the longitudinal dynamics of the vehicle do not depend directly on the performance of the fuel cell system and (ii) kinetic energy can be recuperated and stored in the battery. 

PEM fuel cells are in development to be ultimately deployed in the real world. The real world can vary considerably, from indoor use in buildings or warehouses to outdoor use under arctic conditions. Load variations can vary from continuous idle with occasional periods at maximum power for backup power systems, to highly dynamic operation in transport applications or working at continuous power for Combined Heat and Power systems. The level of control over all relevant parameters can be limited in a fuel cell system, and malfunctioning of control hardware can lead to conditions that fall outside the intended operating window. When compared to testing an MEA in a fuel cell laboratory in test hardware that excludes all influences but those deliberately applied by the operator, a large number of imperfections can be listed ... 

---