Synchronized Switch Harvesting on Inductor Interface to Promote Piezoelectric Stack Energy Harvesting From Human Walking

In this paper, a self-supported power conditioning circuit is developed for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on a synchronized switch energy harvesting on inductance (SSHI) interface and a peak detector topology, the power conditioning circuit is designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, e.g. standard energy harvesting (SEH) circuit, series-SSHI and parallel-SSHI are compared in experiments to find which one is the best suit for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 85% more power than the SEH counterpart, while the use of series-SSHI circuit demonstrates the similar performance in comparison to the SEH interface. The reasons for such a huge efficiency improvement by using the parallel-SSHI interface are detailed in this paper.