Design And Implementation Of Indoor Environmental Energy Harvesting Circuit Based On Maximum Power Point Tracking

The wireless sensor network（WSN）node is one of the foundations of the Internet of Things.At this stage,it is mainly powered by batteries,and there are problems such as battery replacement during long-term use.In order to truly realize the long-term maintenance-free operation of WSN nodes,power harvesting has become a research hotspot in recent years.This paper studies and designs an indoor light energy collection circuit.Under normal indoor lighting（200 lux）conditions,the WSN node can achieve energy self-sufficiency through this circuit.Photovoltaic cell modeling and maximum power point tracking（MPPT）are key technologies for improving the collection efficiency during the light energy harvesting process.The current photovoltaic models and MPPT are more for outdoor solar energy collection and other high energy density application scenarios.Because of the characteristics of low indoor light energy density,in order to ensure the continuous and reliable operation of WSN nodes,necessary improvements must be carried to optimize work efficiency of traditional photovoltaic models and MPPT methods.The thesis first studied a modeling method suitable for a simplified model of photovoltaic cells under low-light indoor conditions.Through experimental comparison,the simplified model can accurately predict the output characteristics of photovoltaic cells.The average error under 200lux is 3.37.%,the maximum error is 4.92%.Then,an improved MPPT method based on the traditional disturbance observation method（P&O）is studied.This method uses the proportional relationship between the open circuit voltage(V_OC)of the photovoltaic cell and the maximum power point voltage(V_MPP)to determine the initial value of the disturbance,so that the initial value is selected closer to the maximum power point（MPP）of the PV module.The ratio of the power difference and the voltage difference between the two iterations is used to determine the disturbance step size,so that the number of iterations is less than that of the traditional P&O.P&O simulation results show that the improved P&O tracking speed is 87.3%higher than the traditional fixed-step P&O and 56.3%higher than the variable-step P&O.Simulation results show that the improved P&O method can track MPP faster when used in a variety of photovoltaic cell MPPTs,and has better applicability.Under normal indoor lighting（200 lux）conditions,the efficiency of the indoor light energy collection circuit designed in this paper is 90.48%,and under low indoor light（50 lux）conditions,the collection efficiency is 83.3%.In order to verify the power supply of the light energy collection circuit,a wireless temperature and humidity sensor based on indoor light energy collection is designed.Experiments show that the light energy collection circuit designed in this paper can meet the energy demand of the wireless sensor node working once in 56.6s under the light intensity of 200lux.The paper achieves the maximum power collection of indoor light energy,and successfully drives the wireless temperature and humidity sensor nodes to work under low illumination.