A mechanical solution of self-powered SSHI interface for piezoelectric energy harvesting systems

The synchronized switch interface circuits, e. g., synchronized switch harvesting on inductor (SSHI), can significantly enhance the harvesting capability of piezoelectric energy harvesting (PEH) systems. In these power conditioning circuits, the piezoelectric voltage is flipped with respect to a bias voltage at the instants when the piezoelectric element is at maximum deforming positions. Voltage peak detection and in time switching action are required for implementing these functions. The state-of-the-art solutions are mostly realized by electronic methods, i. e., both functions are carried out by electronic comparators and electronic switches. However, the peak detectors usually introduce switching phase lag; while the electronic switches function only when the vibration magnitude is above a threshold level. When the vibration is lower than such threshold, the SSHI interface shows no improvement. In this paper, we propose a mechanical solution for constructing the self-powered SSHI interface for PEH systems. This technique is realized by installing a low cost vibration sensor switch (VSS) at the free end of a piezoelectric cantilever. It senses the maximum deflecting places of the cantilever and automatically carries out synchronized switching actions. Compared to the existing electronic solutions, this mechanical solution is compact and has relative low switching threshold. Therefore, with this self-powered solution, the advantage of SSHI interface circuit can be sufficiently released, in particular, at low level vibration. Experiment shows the feasibility of this mechanical solution. The advantages and limitations are also discussed in this paper.