Modelagem não linear de núcleos magnéticos aplicada à colheita de energia por indução

Abstract

Inthescientificliterature,energyharvestingtofeedsensornodeinwirelesssensornetworks can be accomplished in several ways: by magnetic induction, by temperature difference between surfaces (thermal energy), by displacement/movement devices (kinetic energy), and others. Some works with magnetic energy harvesters take advantage the magnetic field produced by the mains electrical current (60 Hz) to supply these sensor nodes, through the principle of magnetic induction. Part of these works neglects the effects of hysteresis or saturation in the device’s magnetic material, which can lead to lower energy harvesting efficiency. To increase the efficiency of these devices, in this work is presented a nonlinear model of the magnetic harvester, whose structure is similar to those used in current transformers (CTs). The material in which the core is formed is a nanocrystalline alloy with very high relative magnetic permeability (greater than 100,000), different from the conventional materials used and with high non-linearity. The flux density and magnetic field in the harvester are modeled using Maxwell’s equations. A nonlinear constitutive relation using the hyperbolic tangent function is applied to approximate the phenomena of hysteresisandsaturationintheCT.Fromtheequationsobtained,theoutputvoltageofthe CT can be calculated and expressed by nonlinear differential equations whose resolution is given by numerical computational methods. To solve such equations the MATLAB© software was used. Experimental data (voltage, secondary and primary currents) were collected for various harvesters changing their dimensions, the number of secondary turns and the primary electrical current levels. From these data the hysteresis loop of the CTs was extracted and their magnetic parameters (for example the coercive field strength and saturation magnetic flux density). In addition to the nanocrystalline alloys, toroidal ferrite cores were used to verify if the model can reproduce the operation of traditional magnetic materials used in CTs. Simulation and experimental results were compared to validate the proposed model. It was verified that the model reproduced the operation of a nanocrystalline harvester and a ferrite harvester, with power harvested relative error (experimental versus simulated) less than 5% and less than 8%, respectively.