Dynamics and Control of a Portable DMFC System

The current state of research on direct methanol fuel cells focuses heavily on the cell itself, with only a small minority of published articles about the management of the complete DMFC system. It is of particular importance to learn about the dynamics and control of such systems in order to provide autonomous and robust operation in spite of changing environmental conditions. We simulate and analyse a reference DMFC system consisting of, besides a model of the fuel cell, a mixer, coolers, separators, pumps and a fuel tank. A control analysis of a DMFC system is presented, to understand which variables are to be controlled by what means, and what constraints the system sets on the control loops. Some apparently negative phenomena can be beneficial to control performance: methanol cross-over stabilises the concentration dynamics and allows the usage of simple feedforward controllers. A portable DMFC system may be used in various environments, with very different environmental conditions. It is therefore explored how these conditions influence the system’s operation and control strategy, especially in regard to environmental temperature and humidity. The current implementation of the model has been designed to study the long-term transients, such as overall anode-loop water and energy holdups, assuming pseudo-steady state for most units.