Comparisons between Parallel- and Series-SSHI Interfaces Adopted by Piezoelectric Energy Harvesting Systems

Advances in piezoelectric energy harvesting have motivated many research efforts to propose suitable electronic interfaces for power optimization. Two kinds of electronic interfaces are currently used in literature. The common one is the standard interface which includes an AC/DC rectifier followed by a filtering capacitance. Another recently emerged one is the 'synchronized switch harvesting on inductor' (SSHI) which is added to the piezoelectric element together with the standard DC technique. It has been shown that the latter has several advantages over the former; however, the effect of frequency deviation from resonance on the electrical behavior of an SSHI system is not taken into account from the original analysis. We here propose several improved estimates for both Parallel- and Series-SSHI interfaces accounting for this effect, and make comparisons between these two. It shows that both Parallel- and Series-SSHI systems exhibit significant improved bandwidth, while the electrical behavior of the Parallel-SSHI (Series-SSHI) system is similar to that of a strongly coupled electromechanical standard system operated at the short (open) circuit resonance.