  An adaptive operation strategy for on-demand control of active direct
methanol fuel cells (DMFCs) is proposed as an alternative method to enhance the
voltage stability. A simplified semi-empirical model is firstly developed to
describe I-V relationships based on uniform-designed experiments. It is then
embedded into multi-objective optimizations to construct the adaptive operation
strategy. Experimental studies are implemented on different DMFC systems to
validate the proposed semi-empirical model, control strategy and system
response to operational adjustments. Numerical simulations are also performed
to investigate the underlying mechanisms of the proposed adaptive operation
strategy. The results show that the adaptive operation strategy provides
possibilities for voltage stability enhancement without the sacrifice of energy
conversion efficiency. The adaptive operations are also found to be able to
extend the range of operating current density or to decrease the voltage
deviation according to one's requirements. Moreover, the response of DMFCs to
operational adjustments is quick, which further validates the effectiveness and
feasibility of the adaptive operation strategy in practical applications. The
proposed strategy contributes to a guideline for the better control of output
voltage from operating DMFC systems.
