Impact of Duffing and Piezoelectric-Coupling Nonlinearities on Piezoelectric Vibration Energy Harvesting

This article studies the impact of intrinsic nonlinearities on the system-level performance of piezoelectric vibration energy harvesters. The study focuses on harvester operation involving realistic large accelerations at the frequency of its designed linear resonance. It is experimentally observed that two intrinsic nonlinearities are required for nonlinear modeling, namely a mechanical (Duffing) nonlinearity and a piezoelectric-coupling nonlinearity. One goal of this article is to develop a modeling and analysis framework that enables the study of these nonlinearities as they interact with realistic interface circuits. Another goal is to use the framework for benchmarking performance differences between linear harvesters and their nonlinear counterparts. To these ends, this article: 1) presents an accurate equivalent circuit model of piezoelectric vibration energy harvesting (PVEH) systems that captures the aforementioned intrinsic nonlinearities; 2) demonstrates model validity over varying levels of nonlinearity (induced by varying vibration acceleration) through ac-input–ac-output experiments; and 3) employs harmonic balance analysis to study the impact of each nonlinearity on optimized system output power and voltage with optimal load–impedance tuning. Key findings of this article are: 1) both nonlinearities reduce maximum output power at resonance despite optimal tuning and 2) nonlinearities cause additional terminal voltage build-up under tuning for optimal power. Practical voltage constraints on the interface electronics limit the tuning range due to voltage buildup, further degrading output power. For both reasons, a purposely designed linear piezoelectric vibration energy harvester is a better choice vis-a-vis its nonlinear counterpart for applications targeting maximum output power at nominal linear resonance frequency even in the presence of large accelerations.