Design and implementation of an interface circuit for piezoelectric energy harvesters

Chamanian, Salar
Micro-fabricated piezoelectric transducer is a prominent harvesting method due to its small size and relatively high energy density. However, the available interface circuits (IC) in the literature for piezoelectric energy harvesters (PEH) are generally designed for macro-scaled versions having a power output in the range of hundreds µW. The efficiency of such systems is significantly diminished when input power drops to tens of µWs or less, which is the pertinent power output range for micro-fabricated devices. Therefore, it is necessary to develop efficient electronics to extract energy from low output power levels of Microelectromechanical systems (MEMS) piezoelectric energy harvesters. The main aim of this thesis is to develop ICs that can efficiently extract energy from the MEMS piezoelectric energy harvesters and charge storage element for powering up micro-electronic devices. In the first IC, a novel multi-stage energy extraction method is proposed to optimize the implementation of the synchronous electrical charge extraction (SECE) converter. This optimization allows downsizing of the external inductor without affecting the power-conversion efficiency. Then, a charge management approach is presented to speed up the charging of the large storage element. The advantage of this method is that it accelerates the transition from passive mode to active mode. Several circuit techniques are introduced to enhance practicability of the energy harvesting IC. An autonomous system is achieved through a start-up circuit with power management circuit that initiates the circuit from no primary charge. Implementations of active negative voltage converter and new ultra-low-power peak detector expand operating frequency range of the IC from 100 Hz to 4 kHz. Finally, self-adapting multi-stage energy extraction (MSEE) enhances power conversion efficiency for a wide input-power range. Maximum charging efficiency of 84 % is achieved with a 1 mH external inductor, while MEMS PEH is excited at 390 Hz. Second IC introduces a novel nonlinear switching technique aiming to boost extracted energy from low coupling factor PEHs and provide load-independent energy extraction with a single inductor. The idea is to enhance effective damping force of the PEH by processing piezoelectric voltage through a set of switches and an inductor. A novel maximum power point (MPP) sensing approach is proposed to achieve the optimal operation point of the proposed circuit regardless of input excitation level, for the first time in literature. The IC can efficiently harvest energy from shock vibrations, as MPP circuit adjusts optimal point regardless of the variation in the available energy on PEH. In the end, an efficient hybrid energy-harvesting interface is presented to simultaneously scavenge power from electromagnetic and piezoelectric sources, while driving a single load. The total simultaneously extracted power from both harvesters is more than the power obtained from each independently. The hybrid IC reaches up to 90% conversion efficiency with output power level of 100 µW. A wearable harvesting prototype consisting of custom-made electromagnetic harvester, off-the-shelf PEH, and the proposed interface circuit is built and tested to harvest energy from body movement.
Citation Formats
S. Chamanian, “Design and implementation of an interface circuit for piezoelectric energy harvesters,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.