| Vibration energy harvesting technology can capture energy from mechanical vibrations and convert it into electrical energy.Mechanical vibrations are everywhere and not limited by environmental weather,temperature or other conditions,which have a great potential.It is expected to be a supplementary energy and eventually replace the battery for various ultra-low power consumption micro-electronics permanently.Currently,the researches on piezoelectric or electromagnetic vibration energy harvesting(PEVEH or EMVEH)are relatively abundant.However,there are relatively few researches on the piezoelectric-electromagnetic hybrid vibration energy harvesting(HVEH)and their energy extraction techniques.Due to the advantages of a HVEH in the final output power,electromechanical conversion efficiency,operating frequency bandwidth and the optimal load range,it has become a hot research field in vibration energy harvesting.In this thesis,the dimensionless parametric model of a HVEH is established,and the effect of each dimensionless parameter on the performance of a HVEH is obtained.Then,the parameter tuning strategy based on nonlinear magnetic force is proposed,which can improve the environmental adaptability of a HVEH.Meanwhile,a series of the power extraction interface techniques based on the adaptive impedance matching and controlled induced damping are developed for a PEVEH,an EMVEH and a HVEH.In addition,the corresponding technical verifications are carried out from the theoretical and experimental aspects and many useful conclusions are obtained too.The main research works and innovations of the submitted thesis are summarized as follows:(1)A full dimensionless parametric model of a HVEH is established.The effects of different electrical load conditions,structural parameters and electromechanical coupling levels on the performance of a HVEH are analyzed.When both of the piezoelectric and electromagnetic transduction mechanisms are weak or medium coupling,the maximum normalized power of a HVEH is affected by both of the two transduction mechanisms and the ultimate value is obtained only if they are matched;when one of the two is strong coupling,the ultimate value can be easily reached.The experimental results show that the optimal load powers are 1.42 m W,2.18 m W and 2.26 m W for piezoelectric,electromagnetic and hybrid transduction in the HVEH prototype,respectively and the corresponding energy conversion efficiencies are 0.15,0.25 and 0.41.The optimal load power and efficiency of the HVEH prototype are increased by 25.6% and 112% respectively compared with the average of the former two as well as the optimal load range.(2)A parameter tuning strategy based on nonlinear magnetic force for a HVEH is presented.The structural dynamic distributed parameter modeling for a forced cantilever beam and the lumped parameter modeling for a closed magnetic structure with an adjustable air gap are performed;based on it,the effects of magnetic force on the natural frequency and electromechanical coupling characteristics of a HVEH are explained.The experimental results show that the equivalent stiffness of the beam ranges from 1475 N/m to 8518 N/m,the 1st modal frequency ranges from 25.5 Hz to 62 Hz,the dimensionless square piezoelectric force-voltage factor ranges from 0.031 to 0.135,the dimensionless square electromagnetic force-current factor ranges from 0.172 to 1.073.The experimental results are in good agreement with the theoretical model.(3)A novel online source impedance evaluation method based on PWM duty-cycle active disturbance is proposed,and a maximum power extraction technique based on adaptive impedance matching is realized.The experimental prototype circuit extracts 1.32 m W and 1.16 m W powers from the PEVEH prototype with 0.4 g and 88.2 Hz acceleration and the EMVEH prototype with 0.12 g and 19.3 Hz acceleration,respectively,reaching 75.2% and 39.9% of their theoretical maximum performance.Base on it,an adaptive multi-load tuning strategy based on genetic algorithm is developed for a HVEH,which realizes the maximum power extraction under the case of multi-port output.The experimental prototype circuit extracts 2.48 m W powers from the HVEH prototype with 0.3 g and 33.5 Hz acceleration,which reaches 84.1% of its theoretical maximum performance.(4)A power extraction technique based on controlled induced damping is presented.The relation between the extracted power and the closure duration time of the synchronized switch and the optimal closure duration time under different electromechanical coupling conditions is deduced.Based on the published SECE and SMFE extraction techniques,another three novel extraction techniques called piezoelectric controlled synchronized switch harvesting technique(P-CSSH)for a PEVEH,electromagnetic controlled synchronized switch harvesting technique(E-CSSH)for an EMVEH and controlled hybrid synchronized switch harvesting technique(H-CSSH)for a HVEH are put forward,respectively.The experimental results show that the H-CSSH technique extracts 5.67 m W powers from the coil-optimized HVEH prototype under 0.3 g and 33.5 Hz acceleration,which makes a great performance improvement. |
