Research On Key Technology Of Adaptive Energy Storage Management Under Hybrid Energy Harvesting Model

With the rapid development of wireless sensor networks,the power supply problem of wireless sensor nodes has become a bottleneck for development.The microenergy harvesting technology provides a new energy solution for wireless sensor nodes,which is self-powered by collecting solar energy,electromagnetic energy,and thermal energy.Micro-energy harvesting technology can effectively reduce the cost of battery replacement in traditional wireless sensor network nodes,thus effectively extending the life of wireless sensor networks.However,the current wireless sensor networks using micro-energy harvesting technology still have the following problems:(1)Micro-environment energy stability is low.Micro-environment energy is greatly affected by environmental factors,and there are many limitations in the single environmental energy harvesting power supply method,and it is impossible to achieve uninterruptible power supply of the same order of magnitude;(2)The node energy management mismatch.There is always a large amount of time mismatch between the energy harvested and the energy required to operate the wireless sensor node.And the higher energy conversion ratio in the energy harvesting management architecture results in lower end-to-end energy conversion efficiency of the system architecture.This causes a waste of energy harvesting.Aiming at the above problems,this paper proposes a hybrid low-frequency electromagnetic field and solar energy harvesting system and adaptive energy storage management control method under the hybrid energy harvesting model.The main work of this paper is as follows:(1)The design of far-field “I-shaped” harvester is proposed.Based on the lowfrequency electromagnetic field near 700 A high-voltage transmission line,the proposed far-field harvester can harvest 0.17-0.46 mW at distances of 2-6 meters above the ground.Further analysis and comparison show that the proposed harvester has higher power density and smaller geometric shape than other similar harvesters.The experimental results show that under the external magnetic field of 7?T,the proposed "I-shaped" low-frequency electromagnetic field harvester can independently accomplish the "cold start" and normal operation of the power management integrated circuit,and supply the power to the wireless sensor node.(2)Aiming at the problem of low energy stability in a single environment,a hybrid low-frequency electromagnetic field and solar energy harvesting system is proposed.Through the further design of a transition circuit and power management unit,the circuit conversion efficiency is up to 61.68% under the maximum power point operating conditions.Finally,the experimental results show that the hybrid solar and lowfrequency electromagnetic field harvester can cross the PMIC "cold start" under the external magnetic field as low as 5.5?T and light intensity of 200 lux,so that the supplied energy can be continues and stable.The proposed hybrid energy harvester can solve the problem of intermittent solar energy and meanwhile increase the total supplied power from the sources.(3)Aiming at the problem of node energy management mismatch,the energy aware unit and the corresponding energy aware strategy are designed to control the energy transfer between the energy storage unit and the wireless sensor node.At the same time,in order to improve the energy conversion efficiency from the back end of the harvester to the load front end,a multi-mode adaptive energy harvesting management method is proposed based on the traditional energy harvesting.To minimize the involvement(charging or discharging)of a battery in the voltage conversion process,the proposed hybrid energy storage employs both battery and super-capacitor,which increases transient energy buffering capability and reduces the overall power conversion loss.The experimental results show that when the total energy consumed by the load is consistent with the total energy harvested by the harvester,and the active energy consumption of the load is 10 times the energy consumed by the load sleep state,the proposed multi-mode adaptive energy harvesting management architecture improves the end-to-end energy conversion efficiency by 2.75 times compared with the traditional architecture.Effectively reduces losses during energy conversion and improves end-to-end energy conversion efficiency of the energy harvesting management architecture.Compared with a single environmental energy harvesting power supply,hybrid environmental energy has a higher energy density,and can effectively overcome the single energy source by the influence of environmental factors to achieve energy complementarity.The energy aware unit and multi-mode adaptive energy harvesting management method designed in this paper effectively solve the energy mismatch problem and improve the end-to-end energy conversion efficiency.It is of great significance to extend the life cycle of wireless sensor networks and further promote the development of wireless sensor networks.