Experimental investigation on a Fe-Ga close yoke vibrational harvester by matching magnetic and mechanical biases

Abstract The output power generated by a vibrational magnetostrictive energy harvester depends on several parameters, some of them linked to the mechanical source, as vibration amplitude and frequency, others related to design quantities, like mechanical preload, magnetic bias, coil turns and load impedance. Complex models have been developed in literature to reproduce the behavior of these devices. However, for output variables such as power and voltage, one moves in a space of many variables and it is not trivial to reconstruct an overall behavior of the device. The aim of this paper is to provide a wide picture concerning the device behavior investigating experimentally the output power and voltage as a function of the mechanical and especially magnetic bias, varying the amplitude and frequency of the driving vibration. A galfenol rod (Fe 81 Ga 19 ) sample inserted in a three-legged magnetizer is utilized to vary the magnetic bias and to provide the flux closure to the sample, while a dynamic test machine provides both the mechanical bias and the driving vibration at different frequencies up to 100 Hz. The paper analysis has highlighted that the output power and voltage depend on the magnetic bias according to an exponentially modified Gaussian distribution. Keeping constant the other parameters and varying the mechanical bias, a family of modified Gaussian distributions is obtained. Moreover, fixing the electric load, the amplitude and frequency of the vibration, the couple of values "magnetic bias – mechanical preload" corresponding to the maximum output power of the device depicts a linear behavior. The results here obtained point out that it is possible to simplify the design of magnetostrictive energy harvesters and to obtain high output power even with permanent magnets providing a relatively small coercive field. The results have been confirmed by using two yokes equipped with permanent magnets on the external columns. The maximum output average power obtained with permanent magnets has been 796 mW equal to 6.5 mW/cm 3 with a sinusoidal vibration amplitude of 40 MPa at 100 Hz

The Effect of Common-Mode Voltage Elimination on the Iron Loss in Machine Core Laminations of Multilevel Drives

This paper studies the effect of common-mode voltage elimination (CMVE) on the iron loss of electrical machine core laminations under multilevel converter supply. Three identical magnetic ring cores are excited by either a three-level converter or a five-level voltage source converter to study the behavior of CMVE on a three-phase system. Both multilevel converters are controlled by using a space vector pulse width modulation as it is one of the most often used techniques for CMVE. These experimental results are confirmed numerically with a dynamic iron loss model. In addition, the effect of CMVE, at different switching frequencies, on the core loss of a synchronous machine is numerically studied. The results presented in this paper show that the core loss is considerably increased when the CMVE is implemented. However this iron loss increase in five-level drive systems is lower compared to the three-level ones. Therefore, it is important that the designers of drive systems take such effects into consideration.Peer reviewe

Modeling Eddy Current Losses in HTS Tapes Using Multiharmonic Method

Due to the highly nonlinear electrical resistivity of high temperature superconducting (HTS) materials, computing the steady-state eddy current losses in HTS tapes, under time-periodic alternating current excitation, can be time consuming when using a time-transient method (TTM). The computation can require several periods to be solved with a small time-step. One alternative to the TTM is the multiharmonic method (MHM) where the Fourier basis is used to approximate the Maxwell fields in time. The method allows obtaining the steady-state solution to the problem with one resolution of the nonlinear problem. In this work, using the finite element method with the H−φ formulation, the capabilities of the MHM in the computational eddy current loss modeling of HTS tapes are scrutinized and compared against the TTM.publishedVersionPeer reviewe

Identification of Magnetic Properties for Cutting Edge of Electrical Steel Sheets

| openaire: EC/FP7/339380/EU//ALEMElectrical steel sheets of motors and generators are usually shaped to the final form by punching. The punching and other cutting processes generate large plastic deformations and residual stresses. These are known to deteriorate the magnetic properties of the edge region. However, the characterization of this deterioration in the form of magnetic properties is missing. The main aim of this paper is to propose a method to identify the magnetic properties of the edge region based on experimental results. This approach is demonstrated by using previously presented test results for magnetic properties of rectangular strips. The width of these strips is varied, and thus, the share of the edge region to the whole can be used as a variable. Based on this variation, a simple model is developed and the model parameters fitted to the experimental results. The correspondence between the calculated and experimental results is good.Peer reviewe

3D Magneto-Mechanical Finite Element Analysis of Galfenol-Based Energy Harvester Using an Equivalent Stress Model

International audienc

Finite element analysis of magnetostrictive energy harvesting concept device utilizing thermodynamic magneto-mechanical model

This paper utilizes a thermodynamic approach based on Helmholtz free energy density and a finite element model to analyze a galfenol-based magnetostrictive energy harvesting prototype device. An analytical energy density function is first presented assuming an isotropic material for the identification of a magneto-mechanical constitutive law. Contrary to earlier approaches, the constitutive model utilizes magnetic flux density and strain as state variables. This serves as a convenient option when the model is applied in finite element (FE) analysis using formulations with magnetic vector potential and mechanical displacement. The Maxwell and mechanical balance equations are then solved utilizing the constitutive law in an axisymmetric FE model. A prototype device is developed and tested under uniaxial cyclic compressive loading of 100 Hz at different preload and dynamic loading case. Finally, the results from the simulations are compared with the experimental results for validation. The comparison shows that the analytical constitutive model fits well to the magnetization curves measured under static loading. Furthermore, the FE model closely predicts the measured power with some discrepancies in absolute value, but is able to predict the behavior of the device with respect to preload, load resistance and magnetization of the sample, proving to be an effective tool in the design of such devices

Modeling a Fe-Ga energy harvester fitted with magnetic closure using 3D magneto-mechanical finite element model

This paper presents the implementation of magneto-mechanical constitutive law utilizing thermodynamic approach in a 3D finite element solver using COMSOL Multiphysics software. The analytical expression for the magnetic field strength and stress is derived from the constitutive model utilizing magnetic flux density and mechanical strain as state variables. The constitutive model is successfully implemented in commercially available software COMSOL. This implementation allows 3D analysis of an energy harvester device efficiently and accurately. A prototype concept device is developed to validate the model and its implementation. The device is tested under uniaxial compressive loading by varying the preload, dynamic load and magnetic bias. The model is validated by comparing the simulated and experimental results. The comparison shows that the model can reasonably predict the optimal value of the preload and magnetic bias yielding maximum power and is able to follow the measurement trends. This model can be used as a suitable tool to analyze the behavior of the concept energy harvesters and determine the optimal design parameters.Peer reviewe