Research On Dynamic Characteristics Of Bistable Piezoelectric Cantilever Power Generation Systems

Low-power requirements of microelectromechanical system (MEMS) enableenergy extraction from ambient vibrations. One of the common power generationstructures is the piezoelectric power generator. There are many researches on linearpiezoelectric power generation systems which have high output efficiency atresonance excitation. But the ambient vibration is generally non-periodic, random andbroandband, it is hard for linear system to work at resonance state. While bistablepiezeoelectric power generators can produce large amplitude motion under periodicand random excitation, which are most possible to realize power generation usingambient vibration. So it becomes a research focus in recent two years.The response characteristics and influencing factors of large amplitude motion ofbistable piezoelectric power generators are studied by numerical calculation,analytical analysis and experiment, it has important significance for designing andapplication of the bistable piezoelectric power generation system. The main researchwork and results in the thesis are as follow:1. The main research methods of piezoelectric power generation system, themethod of realizing resonance on a wide frequency and the research status of bistablepiezoelectric power generation system are summarized. Besides, the general analyticmethods of nonlinear system and Melnikov method are introduced.2. A magnetic force model and a lumped parameter model of piezoelectriccantilever power generation system are established. The response characteristics ofthe system are studied numerically. The results show that the frequency response has abroadband and the beam undergoes large-amplitude motion at low frequency and lowamplitude of the excitation. By the Incremental Harmonic Balance method(IHB), theelectrical performance of the bistable piezoelectric power generation system isanalyzed. It is shown that the jump phenomenon is present on theamplitude-frequency response curve, and with magnetization increasing, the curveoffsets to the right, the frequency band is broadened, and the value of maximumamplitude is increased. In addition, the generation power reaches the maximum byproper selections of resistance. Comparison with the linear piezoelectric powergeneration system shows the bistable piezoelectric power generation system hashigher power under a lower broadband frequency. 3. The chaos threshold of the bistable piezoelectric power generation system iscalculated by the first and second order Melnikov function respectively. The effects ofexciting frequency and impedance item in chaos threshold value expression areanalyzed, and the excitation frequency and resistance values are found which have themost influence on chaos threshold value. The precision of the second order Melnikovfunction is44%more than the first order. The attraction of the large amplitude motionunder different excitation and resistance parameters is given.4. The effect of noise intensity, load impedance and initial value on the systemresponse under random excitation are studied numerically. The time interval of thejump between two equilibrium points is reduced as the noise intensity increasing.There is a matching impedance making the generation power maximum under randomexcitation being same as harmonic excitation. The initial value and impedance willinfluence motion of the system, being proved by drawing the attraction domain oflarge amplitude motion.5. A bistable piezoelectric cantilever power generation device is designed andmanufactured. The response of the bistable system under harmonic excitation andrandom excitation are measured respectively. Under harmonic excitation, thefollowing conclusions are proved by measuring the responses under different excitingfrequency, excitation amplitude, load impedance, magnet distance and initial value.firstly, the bistable piezoelectric cantilever power generation system is suitable forworking at low frequency; Secondly, the system has high energy escaped frompotential well when the excitation amplitude increases, the output voltage is higher, aswell as the frequency range is wider; Thirdly, under a low excitation frequency, thebistable system has higher amplitudes than that of a linear system; Finally, thegeneration power reaches the maximum by proper selection of load resistance and thesystem will be attracted to a large amplitude montion by changing the initial value.Under random excitation, the effects of excitation intensity and load impedance on theresponse of the bistable system are measured, and the experiment results are identicalwith the theoretical calculations.By aforementioned work, the dynamic and generating characteristics of thebistable piezoelectric power generation system are overall obtained, and the influencelaw of main factors on large amplitude periodic motion and chaos are grasped.Because the model of piezoelectric cantilever power generation system is establishedbased on actual physical parameters, the conclusions of this paper can provide concrete guidance for designing and optimization of the bistable piezoelectric powergeneration structure.