Research On The Nonlinear Coupling Mechanism And Dynamic Characteristics Of A 2-DOF Multi-stable Piezoelectric Vibration Energy Harvester And Its Power Extraction Circuit

In the past decade,with the rapid development of micro-robot technology,wireless sensor technology and internet of things technology,low-power electronic products such as wireless sensor nodes have been widely used.At present,most low-power electronic products are mainly powered by batteries.Traditional battery power supply not only has high cost,large volume,short service life and inconvenient replacement,but also pollutes the environment due to improper recycling.Piezoelectric energy harvester(PEH)is a new type of electromechanical coupling device,which converts the vibration energy in the working environment of low-power electronic products into electric energy.It has the advantages of small size,high energy density and environmental protection,and is very suitable for the power supply requirements of microelectronic devices.How to efficiently convert vibration energy in the environment into electric energy is a hot topic in the field of micro-energy.The main research contents of this paper include the following three parts:(1)In order to overcome the problems of narrow working frequency band and low energy conversion efficiency of single-degree-of-freedom energy harvester,a2-DOF multi-stable piezoelectric energy harvester based on magnetic field enhancement and elastic amplification is proposed.The structure principle and main working mechanism of the new energy harvester are introduced.The results show that increasing the excitation amplitude,horizontal magnetic moment and mass ratio can improve the effective bandwidth and output power of the system,and the minimum frequency that can cause inter-well motions are decreased.On the contrary,increasing the stiffness ratio and the distance between external magnets is not conducive to the inter-well motions of the system under the action of low frequency excitation,and the frequency band range of inter-well motions is obviously reduced.Finally,the prototype was developed and the experimental test platform was built.The experiment proved the correctness of the simulation results.(2)In order to convert the collected AC electric energy into DC electric energy and provide DC power supply for subsequent low-power electronic products,a nonlinear standard DC interface conversion circuit based on diode rectification and filtering is proposed based on the above-mentioned 2-DOF tri-stable piezoelectric energy harvester model.The results show that when the load resistance is increased,the output voltage increases rapidly to a certain value and then tends to be stable,while the output power increases rapidly and then decreases slowly.With the increase of excitation frequency,the rectified voltage shows a trend of first increasing and then decreasing.And the output power of AC circuit is higher than that of standard rectifier circuit.However,when the electromechanical coupling coefficient is high,the amplitude of the standard rectifier circuit is higher than that of the interface of the rectifier circuit and decreases obviously with the increase of the coupling coefficient,while the power of the AC circuit is higher than that of the rectifier circuit.(3)In order to further improve the energy extraction efficiency of the interface circuit,a parallel synchronized switching harvesting on inductor circuit(P-SSHI)and series synchronous switching harvesting on inductor circuit(S-SSHI)are designed.The results show that the range of electromechanical coupling coefficients of AC circuit and DC circuit with inter-well motions is large,while P-SSHI circuit and S-SSHI circuit increase their power at the expense of narrowing the range of coupling coefficients.Under the weak coupling coefficient,S-SSHI circuit is better than P-SSHI circuit when the excitation frequency is low and the load resistance is small,and P-SSHI circuit has more advantages when the excitation frequency is high and the load resistance is small.Under the strong coupling coefficient,different circuits can affect the displacement amplitude of the system.Among the four interface conversion circuits,the DC circuit has higher displacement amplitude,rectified voltage and output power than the other three circuits.Then,the principle prototype is developed,and the experimental test platform is built.The experiment proves the correctness of the simulation results.Finally,by synthesizing the above four circuits AC、 DC、 P-SSHI and S-SSHI,the performance of the four circuits is compared and analyzed,and the best working conditions of the four circuits are determined,which provides theoretical and experimental guidance for how to select the appropriate interface circuit.