Time slot optimization algorithm for multisource energy harvesting systems

This paper proposes an algorithm that can maximize the total harvested energy of a single-inductor buck-boost converter operating with multiple input energy sources. It does so by dynamically adjusting the turn-on times and allocating the available time slots for the individual input sources in such a way that all the sources require equal turn-off times for the buck-boost converter to meet the zero-current switching (ZCS) condition. The prototype energy-harvesting IC fabricated in 0.25μm CMOS can charge a 3.3V lithium battery with a delivered power ranging 0.5-5mW utilizing up to four different energy sources simultaneously. The controller itself consumes only 8μW. The experimental results show that the proposed time-slot optimization algorithm can achieve the overall combined power efficiency up to 73.3%, which is a 23% higher than the one with fixed, equal time-slots.