Optimal Operating Concentration Control for Direct Methanol Fuel Cell System by Considering Energy Conversion Efficiency

Direct methanol fuel cell (DMFC) is considered as promising portable power supply at hectowatt level due to its low working temperature and high energy density. This article investigates a sliding mode control to generate stable operating methanol concentration for DMFC system by considering energy conversion efficiency according to different load demands. The model of DMFC system is established to describe the material flow as well as output performance. To achieve the maximum energy conversion efficiency under the required power demand, the reference methanol concentration is determined by analyzing the DMFC system output power as well as the reaction/crossover methanol flow rate. The sliding mode algorithm is adopted to track reference methanol concentration and the simulation results show that compared with fixed methanol concentration (e.g., concentration of 0.3 mo1/L and 0.4 mol/L), the proposed optimal methanol concentration can increase the energy conversion efficiency by 2.3% and 5.6%, as well as reduce the methanol consumption by 8.6% and 18.9% respectively.