On The Study Of Nonlinear Parallel Piezoelectric Energy Harvesting And Its Efficiency

The vibration sources are common in our daily life.Piezoelectric energy harvesting of vibration is one of the hotspots of current energy collection.Although the nonlinear bi-stable piezoelectric harvester overcomes the problems existing in linear piezoelectric harvesting system,there are still some problems,such as too small output current and it is difficult to charge the battery and other energy storage equipment efficiently.Encouraged by the idea of linear parallel piezoelectric harvester,nonlinear parallel piezoelectric energy harvesting system is presented and studied in this thesis.After establishing the dynamic model of the nonlinear parallel piezoelectric energy harvesting,the harvesting efficiency of the system is studied using the numerical method,and some conclusions are obtained which are helpful for designing of the energy harvester.The main research work and conclusions of this thesis are as follows:1.The physical structure and dynamic model of the nonlinear parallel piezoelectric energy harvesting are established.The dynamic model of the system can be obtained by coupling some of single nonlinear bi-stable harvester equation.The results of simulation show that the other beams must be in periodic motion as long as one of the parallel cantilever beams is in periodic motion.And when one beam is in chaotic motion,the other beams are either in chaotic motion or in quasi-periodic motion.For the specific section of system parameter,the average output power of the parallel energy harvester is the product of the average output power of the single harvester and the parallel number,and the output current is also the product of the output current of the single harvester and the parallel number.It is the advantages of nonlinear parallel piezoelectric energy harvesting system.2.It is found that the nonlinear parallel piezoelectric energy harvesting will also come with "frequency hopping".When the "frequency hopping" occurs,the cantilever vibration transition from periodic motion between the wells to quasi periodic or chaotic motion between the wells,then transition from the quaesi periodic or chaotic motion of the well to the multi periodic motion in the well,and then the periodic motion is stabilized in the well with a very small range of frequency.It is found that in order to avoid the "frequency hopping",the system parameter should be on the side of the chaotic region divided by the edge of chaos,which can be determined by the Melnikov method.It is also found that the influence of the change of the parallel number on the edge of chaos is not obvious,but the influence of the change of equivalent nonlinear stiffness on the edge of chaos is obvious.3.There is an obvious periodic motion region between two chaotic motion regions of bi-stable nonlinear energy piezoelectric harvester.The width of the region is named as the periodic motion width.The effective working band width refers to the frequency width in which system can be stabilized without or only at very few frequencies at which the index of energy harvesting,P,fluctuates.The results show that the lumped parameters of system have obvious influence on the width of the periodic motion and the effective working band width,but the parallel number has no obvious influence on the width of the periodic motion and the effective working band width.