Computational and Experimental Efficiency Investigation of Nonlinear Energy Harvesting Systems Based on Monostable and Bistable Piezoelectric Beams
G. C. Kardarakos1, D. Varelis2, N.A. Chrysochoidis1, P. Vartholomeos3, N. Leventakis3, N. Margelis3, T. S. Plagianakos3, G. Bolanakis3, D. A. Saravanos1, E. G. Papadopoulos3
1Structural Analysis and Adaptive Materials Group, Department of Mechanical and Aeronautical Engineering, University of Patras, 26500 Patras, Greece
2Department of Aeronautical Sciences, Hellenic Air Force Academy, 13672 Athens, Greece
3Control Systems Lab, School of Mechanical Engineering, National Technical University of Athens, 15780 Athens, Greece
Over the last decades, various researches have focused on the conversion of available energy which is usually dissipated in the form of heat i.e. from oscillated structures, into usable electric energy, providing an alternative power supply for low-power devices. One of the most promising and frequently encountered ways to achieve this goal seems to be via electromechanical energy conversion of piezoelectric composite strips and plates undergoing mechanical vibrations. Current research attention is focused upon nonlinear piezoelectric energy harvesters (PEH) based on buckled (monostable and bistable configurations) strips and plates. These configurations are deemed to be efficient in electromechanical energy conversion within a broadband vibration frequency range. However, from the aspect of simulation capabilities most researches are based on simplified nonlinear models (Duffing oscillators and single mode vibrating systems) which predict the dynamic behavior of the harvesting device but lack accuracy.
The proposed paper focuses on the application of a computational tool based on coupled electromechanical nonlinear structural mechanics to provide robust predictions for the nonlinear dynamic response of vibrating piezoelectric buckled plates and strips. Subsequently the coupled electromechanical model combined with the presence of an electrical circuit connected to the terminals of the piezoelectric will realistically simulate the oscillatory response of the structure. This model will provide accurate simulations of the complex nonlinear dynamic behavior and electromechanical efficiency of PEH, enabling detailed tailoring of the structural and operational parameters of the PEH according to the application operational conditions achieving the maximum system energy conversion efficiency. Studies of the current work will focus on the presence of resistive and inductive loads connected to the piezoelectric terminals, as the means to enhance electromechanical coupling and energy harvesting.
The proposed PEH setup will be also investigated experimentally. The first objective of this study will be to validate the numerical models. Moreover, three different harvesting circuits will be tested on the experimental set up quantifying the available power on the circuit outputs based on various operational conditions. The harvesting circuits include i) an in-house circuit consisting of a diode rectifier, a capacitor charging from accumulating electric current and a load with a switch which discharges the capacitor, ii) a custom circuit including a full-wave rectifier connected to a commercial ultralow power, high-efficiency energy harvester and battery charger, which implements the maximum power point tracking function (MPPT) and integrates the switching elements of a buck-boost converter and iii) an off-the shelf commercial harvesting module.