Abstract
This paper presents a low-profile and autonomous piezoelectric energy harvesting system consisting of an extraction rectifier and a maximum power point tracking (MPPT) circuit for powering portable electronics. Synchronized switch harvesting on capacitor-inductor (SSHCI) technique with its unique two-step voltage flipping process is utilized to downsize the ponderous external inductor and extend application areas of such harvesting systems. SSHCI implementation with small flipping inductor-capacitor combination enhances voltage flipping efficiency and accordingly attains power extraction improvements over conventional synchronized switch harvesting on inductor (SSHI) circuits utilizing bulky external components. A novel MPPT system provides robustness of operation against changing load and excitation conditions. Innovation in MPPT comes from the refresh unit, which continually monitors excitation conditions of piezoelectric harvester to detect any change in optimum storage voltage. Compared with conventional circuits, optimal flipping detection inspired from active diode structures eliminates the need for external adjustment, delivering autonomy to SSHCI. Inductor sharing between SSHCI and MPPT reduces the number of external components. The circuit is fabricated in 180 nm CMOS technology with 1.23 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active area, and is tested with custom MEMS piezoelectric harvester at its resonance frequency of 415 Hz. It is capable of extracting 5.44x more power compared to ideal FBR, while using $100~\mu $ H inductor. Due to reduction of losses through low power design techniques, measured power conversion efficiency of 83% is achieved at 3.2 V piezoelectric open circuit voltage amplitude. Boosting of power generation capacity in a low profile is a significant contribution of the design.
Highlights
P ORTABLE electronic devices connected to a common network have become ubiquitous owing to the growth in intelligent machine-to-machine interfaces
When adequate amount of charge is accumulated on CST O R, reverse current detector (RCD) and SR latches in switching control block are enabled to sequence Synchronized switch harvesting on capacitor-inductor (SSHCI) phases
SSHCI-maximum power point tracking (MPPT) circuit, for which the die micrograph is depicted in Fig. 17, has been fabricated in 180 nm CMOS technology
Summary
P ORTABLE electronic devices connected to a common network have become ubiquitous owing to the growth in intelligent machine-to-machine interfaces. ÇIFTCI et al.: LOW-PROFILE AUTONOMOUS INTERFACE CIRCUIT FOR PIEZOELECTRIC MICRO-POWER GENERATORS optimized for shock type input excitations thanks to its ultralow power control unit, but its performance gets worse for periodic PEH inputs Another nonlinear switching technique called synchronized switch harvesting on inductor (SSHI) presented in [16]–[20] employs a large inductor to flip residual voltage on PEH capacitance in order to extend charging duration of the battery. The aim of this work is to implement an autonomous lowprofile (i.e. volumes occupied by external components are small) interface circuit and maximum power point tracking (MPPT) system to utilize harvested energy from low-coupled MEMS piezoelectric transducers, and power up WSNs and biomedical devices.
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