Analysis on One-Stage SSHC Rectifier for Piezoelectric Vibration Energy Harvesting

TL;DR

This paper investigates a capacitor-based SSHC rectifier for piezoelectric energy harvesting, demonstrating that increasing the intermediate capacitor size improves voltage flip efficiency towards 50%, reducing reliance on inductors.

Contribution

It introduces a method to enhance the efficiency of SSHC rectifiers by optimizing capacitor values, offering a more compact alternative to traditional inductor-based circuits.

Findings

Voltage flip efficiency approaches 1/2 with larger $C_T$

Capacitor-based SSHC reduces system volume

Efficiency surpasses previous 1/3 benchmark

Abstract

Conventional SSHI (synchronized switch harvesting on inductor) has been believed to be one of the most efficient interface circuits for piezoelectric vibration energy harvesting systems. It employs an inductor and the resulting RLC loop to synchronously invert the charge across the piezoelectric material to avoid charge and energy loss due to charging its internal capacitor ($C_P$). The performance of the SSHI circuit greatly depends on the inductor and a large inductor is often needed; hence significantly increases the volume of the system. An efficient interface circuit using a synchronous charge inversion technique, named as SSHC, was proposed recently. The SSHC rectifier utilizes capacitors, instead of inductors, to flip the voltage across the harvester. For a one-stage SSHC rectifier, one single intermediate capacitor ($C_T$) is employed to temporarily store charge flowed from $C_P$ and inversely charge $C_P$ to perform the charge inversion. In previous studies, the voltage flip efficiency achieves 1/3 when $C_T = C_P$. This paper presents that the voltage flip efficiency can be further increased to approach 1/2 if $C_T$ is chosen to be much larger than $C_P$.