Boost Converter with Harvest Regulator Provides High-Efficiency Power Compression for Bio-Hybrid Fuel Cells and Other Weak Energy Sources

Abstract

Applications for bio-hybrid fuel cells (BHFCs) and other weak energy sources would greatly benefit from highly-efficient power compression that substantially increased the voltage and also allowed intermittent draws of high current. The assumption of a weak energy source necessitates also minimizing parasitic energy draws. We present results for a power compressor composed of a boost converter (variable voltage upconversion), a harvest regulator (matching impedances on the fly), and a bank of low-leakage capacitors (high current draw for short times). The power compressor was not externally powered. Performance was evaluated while connected to two direct ethanol fuel cells (DEFCs) in series, for periods of 3 and 10 days. The DEFCs' design was not optimized for power. They were non-flowing, room-temperature, air-cathode, PtRu/Pt units, which simulated the output of small BHFCs. The power compressor automatically kept the DEFCs close to the voltage yielding maximum power output, which was 400 mV for two DEFCs in series. The output voltage of the capacitor bank was repeatedly raised to 10.25 V and then discharged to 5 V through a resistor. Energy efficiency of the power compressor was uniformly 50%, except for very weak input power.