Strategies of Maximum Power Point Tracking for Sub-mW Benthic Microbial Fuel Cells

Benthic microbial fuel cells (MFCs) are promising alternatives to conventional batteries for powering underwater low-power sensors. Regarding performances (10's mu W at 100's mV for cm(2)-scale electrodes), an electrical interface is required to maximize the harvested energy and boost the voltage. Because the MFCs electrical behavior fluctuates, it is common to refer to maximum power point tracking (MPPT). Using a sub-mW flyback converter, this paper compares the benefit of different MPPT strategies: either by maximizing the energy at the converter input or at the converter output, or by fixing the MFC operating point at its nominal maximum power point. A practical flyback has been validated and experimentally tested for these MPPT options showing a gain in efficiency in certain configurations. The results allow determining a power budget for MPPT controllers that should not exceed this gain. Eventually, considering typical MFC fluctuations, avoiding any MPPT controller by fixing the converter operating parameters may offer better performances for sub-mW harvesters.