Optimization of the Electric Power Harvesting System Based on the Piezoelectric Stack Transducer

Abstract

The generation of electrical power from mechanical motion and structural vibrations is an active area of interest both for scientists and for engineers due to its abilities to serve as the power sources for electric and electronic systems with the reduced power consumption. A key aspect of an system is the power electronic circuitry, which interfaces the piezoelectric (PZT) device with the electric load, as a well-designed circuit can increase the amount of energy harvested. Many different circuit topologies have been proposed and studied to achieve this function. Among these types of circuits are passive, which can include combined resistive/capacitive/inductive load with rectifier, semi-active circuits that open or close a switch, when the peak force is achieved across the device, and also an active energy harvesting, that utilizes a bidirectional switch-mode converter to control the voltage on the electrodes of a PZT device. Most investigations of these systems were performed under low power unimorph or bimorph cantilever PZT energy harvesters. However, multilayered piezoelectric stack, whose layers (thin plates with electrically coating surfaces) are parallel connected, may take very high mechanical excitation and can obtain consequently more electric energy. An important feature of the multilayered PZT stack, which differs from the unimorph/bimorph PZT energy harvester, is the very big electric capacitance that affects on the electric energy flow from the PZT energy source to the electric storage device. At the multiplying these layers the electric capacitance of the device multiplies according to the number of layers, but mechanical and electric losses also increase due to mechanical damping in the bonding interlayers and due to leakage in PZT plates. On the base of the finite element (FE) investigation, we formulate the simplified problem of the energy harvesting, using the lumped model of PZT stack, which experiences the random mechanical excitation in the low-frequency spectrum, and is loaded on a full bridge rectifier, on a filtering circuit with the varied parameters, and charged electric battery. Considering the case of Li-ion battery as an electric energy harvester, we propose the lumped model for the charge-discharge of this battery. Assuming the linearity of the used PZT material and stack’s constraints caused by the external dimensions and the mechanical excitation, we are looking for the parameters of the passive electric load, which provide the maximum achievable values of electric power. Our numerical results demonstrated a very weak dependence of harvested electric energy on the passive circuit’s parameters and the best efficiency of the power PZT stacks with the largest number of thin piezoelectric layers.