Quasi-maximum efficiency point tracking for direct methanol fuel cell in DMFC/supercapacitor hybrid energy system

摘要

Direct methanol fuel cells (DMFC) have been widely researched for applications in portable electronics due to their use of liquid fuel for easy storage and transportation compared to gaseous hydrogen. However, DMFCs performance is strongly affected by methanol crossover that significantly degrades the energy efficiency at low output power, and is characterized by an increasing efficiency at increasing output power. The maximum efficiency point (MEP) is inherently difficult to track due to the commonly unknown methanol crossover rate, but since it is experimentally found to be located very close to the maximum power point (MPP), it is suggested that the MPP can be practically viewed as the quasi-MEP and an alternative tracking approach based on the MPP is proposed for the purpose of MEP tracking. In this paper, a fuel-cell-oriented MPP tracking algorithm based on resistance matching is developed, implemented, and tested in the context of a DMFC/supercapacitor hybrid energy system. To account for the generally slow fuel cell dynamics, the DMFC is constantly tracked at the MPP, while any surplus or deficit power is absorbed or delivered by the supercapacitor bank. The detailed formulation of the algorithm and the power flow design and realization are also discussed.