Research And Design Of High Efficiency Energy Harvester Based On MPPT

With the rapid development of the integrated circuit industry,the contradiction between high power consumption and insufficient battery life of the Io T system is becoming more and more prominent,which has become a difficult point to be tackled in the development of lowpower applications.As a typical representative of green renewable energy,solar photovoltaic cells have been widely used because of their low cost,abundant resources and high energy density.In addition,the load connected directly to the photovoltaic cell is not usually efficient at capturing energy.The energy collector can match the output impedance of the energy source to maximize the energy capture efficiency and achieve the purpose of maximum power point tracking.It is well worth designing the energy harvester based on the Maximum Power Point Tracking(MPPT)algorithm.This paper analyzes the equivalent circuit model of photovoltaic cells,discusses its electrical output characteristics,and studies the common algorithms and detection methods of MPPT.The traditional method is to implement the algorithm by single microcomputer outside the chip with large inductance.This method is not suitable for modern microelectronic system.The capacitive energy collector can be fully integrated into the chip,and the fully integrated system chip has great advantages in terms of functional stability and area.Therefore,the reconfigurable charge pump with series and parallel capacitors is used as the main part of the energy collector,and the range of captured voltage is increased by adjusting the voltage conversion ratio.Based on the research of development status and working principle,the performance index and system framework of the chip are preliminarily determined,and the design and simulation of key circuit modules are completed.The output voltage of the pre-booster module serves as the highest voltage of the system,which can make the switch fully on,and bias the highest potential of the substrate to reduce the leakage loss.The operation mode of cold start,initialization and self-power supply improves the stability of the system.All functions are realized by digital logic module,which further reduces the static power consumption of the system.The mountain climbing algorithm based on lock and back mechanism ensures that the system operates at the maximum power point by adjusting the value of the pump capacitor.This paper adopts 0.18μm 1.8/5V BCD technology to simulate the circuit design,and completes the layout and wiring of key circuit modules.Finally,according to the characteristics of the energy source,the functional simulation of the whole energy harvesting system is carried out under two kinds of illumination conditions.The input voltage range is0.8V to 2.83 V,the output voltage range is 3.3V(adjustable),and the energy capture efficiency is 71%,the overall functions of the chip basically meet the design indicators.