Comparative analysis of the effects of voltage drops in diodes and transistors on piezoelectric energy harvesting efficiency in three types of interface circuits

Abstract To enhance the efficiency of piezoelectric energy harvesting, various interface circuits have been developed, including standard energy harvesting (SEH), synchronized charge extraction (SCE), and both parallel and series synchronized switch harvesting on inductor (P-SSHI and S-SSHI) circuits. However, voltage drops in transistors and diodes prevent the synchronization switch from closing precisely when the output voltage of a piezoelectric energy harvester (PEH) reaches its peak, resulting in a switching delay. The impact of this delay on energy harvesting and storage remains insufficiently understood. This study models and compares the effects of voltage drops in transistors and diodes on energy harvesting and storage in self-powered SCE, P-SSHI, and S-SSHI circuits. Analytical solutions for the voltage variations on energy storage capacitors during each half-cycle are derived, and experimental tests are conducted to validate the theoretical results. A systematic comparison of the energy charging performance is conducted for PEHs under weak, medium, and strong coupling conditions, with a focus on the influence of threshold voltages across transistors and diodes. Results show that switching delays can reduce the energy charged into storage capacitors in systems with self-powered P-SSHI and S-SSHI circuits. The self-powered P-SSHI circuit is most effective for energy charging in PEHs with weak coupling, while the SEH circuit proves most efficient for PEHs with medium or strong coupling.