Study On The Power Management Circuit For Energy Harvester Working In Low Energy Density

With the improvement of technology,Wireless Sensor Network(WSN)is developed in the direction of little volume,small consumption and multi-array.As the basic element of WSN,WSN node has gained more and more attention in the power supply issue.The traditional power supply methods use chemical battery.But with the limit of volume,chemical battery can only carry little amount of electricity,thus cannot meet the requirement of supplying power for a long time.The great number of WSN nodes is a big challenge of the replacement of battery,not to mention the extreme environment,such as high temperature,high voltage environment.However,as the power consumption in WSN node gets lower and lower,it proposes a solution to supply WSN nodes with self-powered(energy harvesting)technology,which harvests the ambient energy in the environment.For the present,the main energy sources are solar energy,vibration energy and electromagnetic energy.The harvested energy can't supply WSN nodes directly.It is necessary to design a power management circuit to provide WSN nodes with DC supply power that meet the demand in power capability and voltage magnitude.However,for a low energy density energy harvester,whose output power is low,the traditional management circuits can only transfer the harvested energy in low power.It leads to high proportion of harvested energy dissipated in the power management circuit,low energy transfer efficiency,and huge wastage of harvested energy.Thus,a novel management circuit is needed for low energy density energy harvesters.Under the direction of Professor Li Ping,this paper presents a quartz crystal resonant management circuit for low energy density energy harvesters.This paper analyses the output characteristic of low energy density energy harvesters,and establishes rectifying model for management circuits in low energy density environment,and explains the reason why energy transmission in low power dissipates large amounts of energy.In the meantime,this paper proposes a quartz crystal resonant management circuit,based on the frequency-conversion matching circuit and the quartz crystal energy storage circuit.The management circuit uses frequency-conversion matching circuit to extract the harvested energy from the harvester efficiently,and move the frequency of output to the quartz crystal's resonant frequency.Quartz crystals which have high quality factor can store the harvested energy with low loss.When the stored energy is high enough,it'll be released quickly,creating high power energy transmission.The intermittent high power energy transmission deduces the dissipated proportion of the total transferred energy.Use 1m F super capacitor as storage capacitor,and test the charging characteristics of the proposed quartz crystal resonant management circuit.For a low energy density energy harvester,which works at 50 Hz and outputs 8V RMS voltage,the quartz crystal resonant management circuit's max charging power is 5.03?W.The charging voltage and charging power are improved by 163% and 110%,respectively,compared with the traditional frequency-conversion matching management circuit.