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Öğe A neural network design for the estimation of nonlinear behavior of a magnetically-excited piezoelectric harvester(Springer, 2018) Çelik, Emre; Uzun, Yunus; Kurt, Erol; Öztürk, Nihat; Topaloğlu, NurettinAn application of an artificial neural network (ANN) has been implemented in this article to model the nonlinear relationship of the harvested electrical power of a recently developed piezoelectric pendulum with respect to its resistive load R (L) and magnetic excitation frequency f. Prediction of harvested power for a wide range is a difficult task, because it increases dramatically when f gets closer to the natural frequency f (0) of the system. The neural model of the concerned system is designed upon the basis of a standard multi-layer network with a back propagation learning algorithm. Input data, termed input patterns, to present to the network and the respective output data, termed output patterns, describing desired network output that are carefully collected from the experiment under several conditions in order to train the developed network accurately. Results have indicated that the designed ANN is an effective means for predicting the harvested power of the piezoelectric harvester as functions of R (L) and f with a root mean square error of 6.65 x 10(-3) for training and 1.40 for different test conditions. Using the proposed approach, the harvested power can be estimated reasonably without tackling the difficulty of experimental studies and complexity of analytical formulas representing the concerned system.Öğe Design and implementation of a new contactless triple piezoelectrics wind energy harvester(Pergamon-Elsevıer Scıence Ltd, 2017) Kurt, Erol; Cottone, Francesco; Uzun, Yunus; Orfei, Francesco; Mattarelli, Maurizio; Özhan, DavutThe features of the new designed and constructed harvester are examined. The harvested power of three piezoelectric layers having different masses (i.e. different natural frequencies) has been explored. These layers have the same length around the harvester body, whereas a permanent magnet (PM) attached to the shaft rotates by low speed wind and this PM repels these three piezoelectric layers with a 120 phase shift. Since PM and the PMs located to the tip of the layers do not contact, this system improves the lifetime of the harvester. The measured harvested power in the low wind speeds (i.e. 1.75 m/s) is of the order of 0.2 mu W. The waveform includes many subharmonic and superharmonic components, hence the total harmonic distortion (THD) is found around 130%, which is fairly high due to nonlinear effects. Although the system shows an high THD, the 20% of the signal can be rectified and stored in the capacitor for the use of harvested energy. A scenario has also been created for a resistive load of R-L, =1 M Omega and 100 k Omega for various wind speeds and it has been proven that the harvester can feed the load at even lower wind speeds. In addition, extra power beyond the usage of the load can be stored into the capacitor. The proposed harvester and its rectifying unit can be a good solution for the energy conversion procedures of low-power required machines. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Design and simulation of a new dual-band RF energy harvester with high efficiency(Institute of Electrical and Electronics Engineers Inc., 2015) Uzun, Yunus; Kurt, ErolIn recent years, it is one of the biggest disadvantages of wireless sensors have vital importance that they are supplied by batteries. It is possible to overcome this deficiency by RF energy harvesting systems. In this work, the system generating electrical energy efficiently from two different RF signals have different frequencies is presented. Compared with conventional single frequency RF energy harvester, with the proposed dual band RF energy harvester, an increase is achieved 39% and 78% for 575 MHz and 900 MHz input frequencies at 0 dBm signal level, respectively. In a wide range of frequencies in the range of 400 MHz to 1000 MHz, the efficiency is obtained over 50% from the proposed system. Thus, the system can be used efficiently in an environment including any one or more DTV and GSM signal. The proposed circuit can be used effectively on the RF signals have the level of more than-15 and-10 dBm. © 2015 IEEE.Öğe Effects of nonlinearities in a magneto-piezoelectric system(Institute of Electrical and Electronics Engineers Inc., 2014) Kurt, Erol; Uzun, YunusThis paper focuses on the theoretical and experimental analyzes on the dynamics of a magneto-piezoelectric pendulum system under the magnetic excitation. Initially, it handles the theoretical modelling of the problem including the mechanical, magnetic and electrical terms of the system. The theoretical formulation of the pendulum system is realized based on the experimental parameters. Then, a detailed experimental survey has been carried out for the system parameters, namely the magnetic field frequency f and amplitude V (i.e. proportional to the amplitude of the field). In the last part, the nonlinear patterns from the theoretical and experimental studies are discussed. It will be pointed out that the periodic magnetic flux can cause different responses in the magneto-piezoelectic system from regular dynamics to chaotic one. Phase space constructions, Poincare sections, FFTs and THDs are determined for certain parameter sets. A sample harvester application of the system will also be introduced at the end of the paper. © 2014 IEEE.Öğe Experimental and theoretical explorations on the buckling piezoelectric layer under magnetic excitation(Springer, 2017) Çelik, Kayhan; Kurt, Erol; Uzun, YunusIn the present study, experimental and theoretical explorations on the buckling features of a wind energy harvester have been performed. The harvester consists of a piezoelectric layer, which has a certain stiffness and voltage conversion rate. A blade rotates on a shaft carrying a magnet and sweeps the tip of the layer causing a serial buckling effect resulting in energy generation. Since the modeling of the buckling under a magnetic strength includes nonlinear terms over displacements, one requires a detailed study on the characteristics of buckling phenomena. It has been proven that the piezoelectric beam having the magnet at its tip can produce regular and chaotic dynamics for different frequencies (i.e. the rotation speed). In addition, there exist a number of quasi-periodic regions on the parameter space. The overall result indicates that the large area of complicated dynamics requires a detailed study in order to stabilize the position and velocity of the layer tip, thereby a much stabilized energy conversion from mechanical to electrical can be obtained. The present survey on the dynamics of the harvester is a new study and is considered as a two-parameter diagram [i.e. the wind speed (frequency) and magnetic strength]. Mainly, single-, double-, triple- and quadruple-type phase space portraits have been observed and the ripples on the maximal and minimal values of the beam velocity have been observed for certain rotation speeds. These results can be used in order to stabilize the harvester in terms of the reduction of total harmonic distortion in the generated waveform.Öğe Explorations of displacement and velocity nonlinearities and their effects to power of a magnetically-excited piezoelectric pendulum(Elsevier Science Sa, 2015) Uzun, Yunus; Kurt, Erol; Kurt, H. HilalThis paper explores the relation of the nonlinearities of displacement and velocity dynamics with the power of a piezoelectric pendulum under a periodic magnetic excitation. Initially, the theoretical formulation including the mechanical, magnetic and electrical terms is realized. Then a simulation study has been done by using the theoretical formulation based on the experimental parameters. Then, a detailed experimental survey has been carried out for some representative system parameters. Results of simulation based on the proposed model are presented and compared with the experimental results. It is observed that the periodic magnetic flux can cause different responses from regular dynamics to chaotic one. Phase space constructions, Poincare sections and FFTs are determined on parameter sets including the excitation frequency f and amplitude U-c of electromagnet. It is proven that the periodic magnetic flux exerts high frequency velocity fluctuations nearby the minimal and maximal values. While the displacement of the tip exhibits a harmonic fluctuation, FFFs prove the high frequency responses in addition to the main frequency. When f differs from the natural frequency of the system f(0), the responses become chaotic. It is proven that lower and higher frequency fluctuations in displacement and velocity, which are different from f(0) decrease the electrical power harvested by the piezoelectric pendulum. However, in the case of rms values of displacement/velocity, the harvested power is perfectly proportional to the rms values. Therefore, useful relations between power and rms values of displacement/velocity have been determined for the estimation of power output in such systems for the first time. The piezoelectric pendulum harvests much energy when f is closed to f(0) and the distance to the magnetic device should be closer in order to decrease the nonlinearities in displacement and velocity. (C) 2015 Elsevier B.V. All rights reserved.Öğe Mitigation of high harmonicity and design of a battery charger for a new piezoelectric wind energy harvester(Elsevier Science Sa, 2018) Bouzelata, Yahia; Kurt, Erol; Uzun, Yunus; Chenni, RachidA new piezoelectric wind energy harvester (PWEH) implementation and its power conversion system design have been studied. The new PWEH is a portable, economic, easy-mounted, and contactless machine exerting the elastic piezoelectric layers with permanent magnets (PMs). Although a single piezoelectric layer has an ideal sinusoidal waveform from its output terminals, the combined rotating system having multiple layers give complicated responses due to the electromechanical damping, high frequency mechanical vibrations and electromagnetic nonlinearities. In the current work, for instance, three layers generate three different waveforms with high harmonics. Thus, the output waveforms of such multiple layer low power-scale systems require special attention to gain the maximal power from such low scale harvesters. Indeed, electrical power generation from complicated voltage waveforms and charging efficiency have become main tasks for those low power systems. The proposed rectifier is joined to a capacitor-inductor output filter to ensure high quality DC - bus voltage by ripple mitigation function. An effective control strategy is also carried out for the voltage - mode control (VMC) method in order to control the DC-DC buck converter in such a way that it may guarantee a smooth output DC voltage. Then the later can be applied to charge storage unit such as a lead-acid type electrochemical battery for the future numerous low power applications. The proposed circuitry is successful to mitigate the harmonics of the voltage waveforms from the terminals of three piezoelectric layers with high THD values (i.e. 169.16%, 51.75% and 42.64%). In addition, the proposed PWEH has an ability to charge the battery with a stable output rectified voltage at 40V by enabling a linear increase in the State-Of-Charge (SOC) from 0% to 18% after 4 s till the battery is fully charged.Öğe Nonlinear problems in piezoelectric harvesters under magnetic field(Springer International Publishing AG, 2017) Kurt, Erol; Uzun, Yunus; Bizon, N; Tabatabaei, NM; Blaabjerg, F; Kurt, EThis chapter focuses on the nonlinear problems in the piezoelectric harvester systems under the magnetic field. In this manner, the chapter initially mentions an introductory section on the studies of piezoelectric harvester dynamics. After the introductory section, the basic properties of the piezoelectric systems and their energy harvester applications will be presented. Since the harvesters have a complicated structure under the magnetic field, the electromagnetic design, modeling and algebraic studies of a novel harvester study will be pointed out. After the presentation of a theoretical outline on the harvester systems, the experimental setups will be explained in detail. Thus, a complete picture of the problem will be produced in order to sustain a comparable study on the theory and experiment. The main dynamic quantities such as displacement and velocity of the vibrating piezoelectric layer as function of the system parameters will be explored. According to results, the effect of periodic magnetic flux can give varieties of responses from regular dynamics to chaotic one. Phase space constructions, Poincare sections and FFTs are evaluated depending on the parameter sets including the excitation frequency f, amplitude Uc of electromagnet and the distance d. It is proven that the periodic magnetic flux can exert high frequency velocity fluctuations nearby the minimal and maximal values of the velocity, whereas the situation differs for the position. Therefore it will be pointed out that the magnetic field mostly governs the velocity by yielding complicated vibrations. According to the detailed analyses, the FFTs prove the high frequency responses in addition to the main frequency. When f differs from the natural frequency of the system f(0), the responses become chaotic. It is proven that lower and higher frequency fluctuations in displacement and velocity, which are different from f(0) decrease the electrical power harvested by the piezoelectric pendulum. Indeed, it is remarkable to get a relation between the rms values of displacement/velocity and the harvested power according to the measurements. Thus this relation can be used to estimate the power output in harvester systems. The piezoelectric harvester generates much energy when f is closed to f(0) and the distance to the magnetic device should be closer in order to decrease the nonlinearities in displacement and velocity. The pendulum-like harvesters as the most preferable ones can be applied to many devices or units as a power source. The maximal power for these magnetically-excited structures can be estimated by the system parameters. At the end of the chapter, the recent techniques of maximal power point tracking (MPPT) and proposed controller units are explained for the piezoelectric harvester systems in order to optimize the harvested power.Öğe Power characteristics of a new contactless piezoelectric harvester(Institute of Electrical and Electronics Engineers Inc., 2015) Kurt, Erol; Uzun, Yunus; Durmuş, CemThis paper reports the preliminary results of a new designed harvester system called as the contactless piezoelectric wind energy harvester (CPWEH). It consists of three piezoelectric layers attached with the non-magnetic bars in different lengths in order to produce maximal power for a wide wind wide speed regime. Preliminary magnetic design has proven that three layers can be excited by the magnetic forces synchronously and this situation prevents to damage the piezoelectric layers since it does not make any physical contact to the layer. According to the results, this new harvester produces electrical power at low wind speeds such as 2.5 m/s. The harvested power can be obtained from the range of 2.5 mW to 17 mW. Therefore the efficiency of the harvester having a single piezoelectric layer has been introduced three times in the proposed design and implementation. © 2015 IEEE.Öğe Power control optimization of a new contactless piezoelectric harvester(Elsevier, 2017) Zulueta, Ekaitz; Kurt, Erol; Uzun, Yunus; Manuel Lopez-Guede, JoseIn this study, we propose an optimization scheme for the control of a piezoelectric wind energy harvester. The harvester is constructed by a blade in front and a magnet in the rear in order to sustain a magnetic repulsion by another magnet located on the stable harvester body in a contactless manner. For such a new harvester, the control scheme is missing in the literature in the sense that the harvester is new and an overall optimization study is required for such a device. In that context, the optimization has been realized by using a new current control law based on the harvester piezoelectric terminal voltage and the layer bending. The proposed control law can impose a second order linear dynamics although the magnetic effects can yield to nonlinear magnetic force relation. In order to improve the new control strategy, a Particle Swarm Optimization algorithm (PSO) has been applied, since there is a nonlinear dependency among the control parameters, the collected energy and the bending force mean values. According to results, the captured electrical power has a high increasing trend with respect to the only-voltage-based (OVB) control as the current study proves. On the contrary, the artifact of the method'is that the obtained power is too low to increase the mean bending forces and it requires much complicated control system. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
