Research On Piezoelectric Energy Harvesting From Bridge Vibrations Induced By Passing Vehicles

The construction of bridges has developed rapidly in the last few decades.The health status of the bridges is vital to the operation of the transportation system.The bridge vibration energy caused by passing vehicles can be transformed to electricity and powering the bridge monitoring system continuously,which can overcome the shortcomings of power supply of the traditional type and is expected to achieve long-term self-powered monitoring of bridges.Under this background,cantilevered piezoelectric energy harvesters are used to harvest energy from bridge vibrations caused by passing vehicles.The research proceeds in three aspects:theoretical mechanism,energy harvester design method and energy storage.The main work and conclusions are as follows:(1)The basic theory of piezoelectric energy harvesting of bridge vibrations induced by moving vehicles is established.Firstly,The distribution parameter dynamical equations of bridges and piezoelectric energy harvesters are established by beam theory,respectively.The functions were solved by modal superposition method,a closed form solution of the voltage output of the PEH under undamped condition is obtained.Then using moving load,moving mass and moving oscillator vehicle model,the effects of the characteristics of the PEH,the fixed position of the PEH,road condition and vibration frequency of the vehicle on energy harvesting are discussed.The research shows that:when the natural frequency of the PEH is close to the natural frequency of the bridge,the harvested energy is proportional to the square of the mode shape at the installation location of the PEH;when the vibration frequency of the vehicle is close to the natural frequency of the PEH or the bridge,the harvested energy curve has double peaks;when the bridge surface unevenness is considered,the energy harvesting prediction results of different vehicle models are quite different.The harvested energy predicted under the moving oscillator model is less than 4%of the predicted result under the moving mass model.(2)Two kinds of PEH design methods are proposed,and the energy harvesting efficiency of the PEHs made in these two design methods are tested through experiment.Firstly,two kinds of PEHs are fabricated and their natural frequencies are matched with the natural frequency of the bridge and the coupling vibration frequency of the vehicle-bridge system,respectively.Energy harvesting experiment is carried out on the vehicle-bridge coupled experimental platform,and then the rationality of the proposed design method is clarified.After that,two typical railway bridge vibrations are measured as the base excitations of the PEHs,and the energy harvesting performance of the PEHs are studied.The study finds that:for the natural frequency of the PEH matches the natural frequency of the bridge,the PEH has a large energy output when the vehicle entering or leaving the bridge,but the energy output is very weak when the vehicle is running on the bridge;if the natural frequency of the PEH matches the vibration frequency of the vehicle-bridge coupled system,the PEH has obvious energy output when the vehicle running on the bridge.When the heavy-duty train just enters the bridge,the PEH can hardly harvest energy.When the train is running on the bridge,the voltage output of the PEH can reach 13V,but the voltage is unstable.When an high-speed train crosses the bridge,the voltage output of the PEH is stable at around 17V.However,due to the short of energy harvesting duration,the harvested energy is only about 1/6 of the harvested energy from the heavy-haul railway bridge vibrations.(3)The full process of energy harvesting analysis is given,which included bridge vibration,energy transfer of the PEHs,interface circuit conditioning and energy storage.Based on the vibrations of the heavy-haul railway bridge and the high-speed railway bridge,the whole processes of energy harvesting are studied.Based on the equivalent circuit method,the electrical equivalent parameters of the environment vibrations and the PEHs are given,and the energy output of the PEH is adjusted by STD or self-powered SCE,P-SSHI and S-SSHI interface circuit.Then a super capacitor is used to store energy.The circuit models of the whole process analysis are constructed in Multisim,and the transient energy storage process analysis is given.The results show that:optimal storage capacitors exist which can help to maximum the energy storing.In order to obtain the highest energy harvesting efficiency,when STD interface circuit is used,the short-circuit and open-circuit resonant frequencies of the PEH should be on both sides of the excitation frequency.When SCE or S-SSHI interface circuits is used,the open-circuit resonant frequency of the PEH should be close to the excitation frequency,and when P-SSHI interface circuit is used,the short-circuit resonant frequency of the PEH should be close to the excitation frequency.The maximum stored energy is smaller than the theoretical prediction value.The STD interface circuit has the largest energy storage efficiency,however,its only 2/3 of the theoretical prediction value.