Optimization Of The Output Power Of Cantilever Piezoelectric Vibration Energy Harvesting System

Piezoelectric vibration energy harvesting method has become the focus of energy harvesting field, for the merit of high electromechanical conversion factor, clean and green, and easy miniaturization. Since the piezoelectric transducer generates the maximum output power at the resonance, the power will drop drastically when the operating frequency deviates from the resonance point. Therefore, how to broaden the band of the energy harvesting system and scavenge more energy at non-resonant point put forward higher requirements for research on piezoelectric energy harvesting. Improving the output power of piezoelectric transducer at the non-resonant point is the ultimate goal.On the basis of the analysis model of the system, the method of optimizing the output power by reactive power compensation is presented.The influences of electromechanical coupling degrees and excitation acceleration to the output power are explored, and the experimental verification are carried out. Finally, the output power characters of standard energy harvesting circuit with parallel inductor are analyzed. The energy storage and management circuit are designed to power the wireless sensor nodes, and its power supply capacity is analyzed.Based on the lumped model of the cantilever piezoelectric energy harvester and the impedance characters of piezoelectric transducer, the optimized series or parallel inductor circuit of cantilever piezoelectric transducer is presented. Firstly, based on the analysis of the electromechanical coupling circuit of piezoelectric transducer with an inductor and load resistance, the matching resistance, inductance, the maximum output power and the power ratios are estimated and the characters of the output power with different reistance and inductance arc studied by simulation. Secondly, from the point of the impedance matching, the output power optimization mechanism of the series or parallel inductor circuit is analysed. Finally, by comparing the power curve of the series or parallel inductor circuit and the non-inductive circuit, its feasibility in improving the output power under the different excitation frequencies is shown.The results show that when the excitation frequency is0.8or1.2times of the resonant frequency, the maximum output power is26.4and18.2times of that of the purely resistive load. The experimental results are in good agreement with the simulation. Besides, the method of putting the existing piezoelectric cantilever beam as a reference for the reverse design is proposed, and the influence of coupling degrees to output power is analyzed by simulation, showing that there is an optimal coupling degree maximized the output power under specific ambient constraints and structural parameters. The output power and the operating band characters of the system are studied under the conditions of three kinds of the excitation acceleration amplitude. The results show that the greater the excitation acceleration, the higher the output power, and the operating band is weakly broadened.The output power characters of standard energy harvesting circuit with parallel inductance at the non-resonant point are explored. Secondly, the characters of the proposed circuit and the synchronized switching harvesting on inductor circuit in improving the output power are given. Finally, the energy storage and management circuits are designed. The experiment shows that, the output power can be improved by adding a suitable parallel inductor and successfully powered the wireless sensor nodes.