Effective Charge Excitation And Output Energy Management For Tribeoelectric Nanogenerator

With the rapid development of electric information techonology,human society steps into the road of intelligence and automation,and the utilization of various resources has gradually entered the stage of refinement.Energy is the propellant for speeding up the development of society.Nowadays,with the increasing development of mobile wearable devices and Internet of Things technology,the high-quality and large-scale centralized energy provided by large-scale power generations cannot satisfy the society any more.Harvesting various low-grade and refined energy which is distributed widely in the surrounding environment,to supply energy for hundreds of millions of distributed electronic devices has become an urgent problem that to be solved in today's society.The various ambient mechanical energy is always random and in low frequency,so it becomes a challenge to harvest such energy efficiently.Triboelectric nanogenerator(TENG)invented by Wang's group in 2012 has become a novel and high efficient energy harvesting technology.TENG has huge potential in harvesting mechanical energy like human motion,rain drop,ocean and wind enegy,etc.and play a key role in biomedical science,chemistry,smart devices and other self-powered systems.Therefore,TENG is crucial for the energy supply of distributed sensors in the internet of things,and has become a research hotspot across multiple disciplines.The output performance of TENG determines and supports its application level and commercial potential from the source.In this article,by combing the electromagnetic theory and electronic technique,we improve the performance of TENG deeply from the output in the front end and energy management in the back end.The content is displayed as follows,(1)Increasing the output charge density of TENG is the key to improve its front-end output.Aiming at the disadvantage of low charge density of friction materials in atmospheric environment,we propose a high-efficiency and universal external charge excitation method.In order to effectively increase the charge density of the main TENG,a common TENG is used to inject charge into the main TENG.Firstly,we established an equivalent model consisting of a main TENG,charge storage capacitance and unidirectional high voltage source.The excitation voltage is generated by the high voltage source to inject charge into the main TENG to improve its charge density.During the subsequent contact separation process,the charge injected under static electricity will transfer back and forth between the main TENG and the charge storage capacitor,resulting in an AC output.Secondly,we used an additional TENG and voltage doubling circuit as the unidirectional high voltage source to generate high voltage.At the same time,the output capacitor in the voltage doubling circuit is also used as the charge storage capacitor to simplify the structure.Finally,we introduced a voltage stabilizing control unit to obtain a stable and adjustable output in case the high voltage could damage the power generation device.When a 5?m kapton dielectric film was used,charge accumulation rate in atmospheric environment of 218 s/(m C m^-2)in the main TENG is achieved,and for the first time,a high charge density output reached1.25 m C/m².Compared with the traditional TENG,the external charge excitation method increases the charge density by 25 times,which breaks through the limitation of the current lack of electrification ability of friction materials(2)Due to the existence of the excitation TENG,the external charge excitation method has slow charge accumulation speed and complex structure,which is difficult to fully meet the actual requirements.Therefore,in this paper,we used the energy generated by the mian TENG itself to supplement the charge,and proposed a self-excitation strategy.A self-excitation TENG composed of a three-layer main TENG and a voltage self-doubled circuit is designed.Among them,through the coupled effect between the main TENG and the external capacitors which can automatically switch between series and parallel,the main TENG achieves the exponential effect of charge self-increase.A high charge density of 1.22 m C/m² and an ultra-fast charge accumulation rate of 23 s/(m C m^-2)were obtained,by using a composite liquid flexible cushion and a 5?m kapton film to increase the interface contact of self charge excitation TENG in atmospheric environment.In addition,even if the main generator has only a very small initial charge,it can achieve the effect of self-excited increase.The self-charge excitation strategy has the advantages of faster charge accumulation,simple structure,easy integration and industrialization,and is complementary to the external charge excitation method.(3)TENG has the characteristics of high voltage and low charge.There is a serious voltage mismatch problem when using TENG to directly drive electronic devices.Therefore,efficient energy management is needed to improve energy utilization efficiency.Switched capacitor converter has the advantages of easy integration,light weight,no magnetism and converting energy in the form of voltage-charge,which is very suitable for TENG.In this paper,we proposed a fractal design based switched capacitor converter,which can upgrade one-dimensional linear discharge network of traditional switched capacitor transducer to two-dimensional planar discharge network,and greatly reduces the output impedance.Besides,it has the advantages of high electrostatic voltage applicability and high conversion efficiency.Based on this,we build a energy management system with dual output modes for TENG.For the first time,we achieved a charge enhancement of more than 67 times and a high power density of954 w/m² in the pulsed mode,and achieved a total energy transfer efficiency of more than 94%in the constant current mode,successfully driving various small electronic devices at low frequency of 1.5 Hz.The concept of dual mode output has an important guiding significance for the development of TENG to the developemnt of multi-functional energy management.At the same time,the non-magnetic propertiy of switched capacitor converter also further expands the practical application of TENG.