This paper presents a system-level design approach for widening the bandwidth and lowering the operating voltage of a piezoelectric vibration energy harvesting system (PVEHS). The proposed strategy involves co-optimization of the two constituent parts: (i) a highly-coupled piezoelectric vibration energy harvesting device (PVEHD) and (ii) a phase-shift tunable parallel-SSHI (PS-PSSHI) interface power-electronic circuit. First, we analyze the interaction between them to achieve an overall reduction of system voltage and to widen bandwidth. Next, a co-designed system is experimentally demonstrated to validate the analysis. The implemented PVEHS consists of (i) a customized PVEHD designed for high electromechanical coupling and well-separated shortcircuit (fSC) and open-circuit (fOC) resonances, and (ii) a tunable PS-PSSHI circuit which has an active rectiﬁcation with low voltage drop to increase system eﬃciency. The system achieves an output power of 148 W with a bandwidth of 81 Hz, an increase of 337% compared to conventional full-bridge rectiﬁer. In addition, the system rectiﬁcation voltage is lowered by 30% which makes it viable to power low-voltage Internet-of-Things sensor nodes.
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