Study On Equalization Circuit For Ultra-Capacitors

The ultra-capacitor is a storage device with high energy,strong power,long cycle life also known as pseudo capacitor and double-layer capacitor.Along with the increase of the focus on ecological environmental protection and green pollution-free energy,the ultra-capacitor as a new type of energy storage devices,owing to its irreplaceable advantages,get more and more attention.In series system of super capacitor group,the dispersions of ultra-capacitor monomer in performance parameters lead to voltage differences and reduce the capacity for energy storage of the system.Therefore,it is meaningful to have voltage balance management for the groups of ultra-capacitors to improve the efficiency of the energy storage.This paper introduces the fly-back converter in detail including the evolution from the Buck-Boost circuit.The structure of the fly-back converter as well as the principle and the continuous and discontinuous,critical three kinds of working condition are introduced based on the equivalent transformation method.On this basis,state space equation for the balancing circuit of ultra-capacitor group in series based on the fly-back converter is established.Through linearization processing,small signal mathematical model of the circuit is obtained.Small signal ac equivalent circuit is also established.The detailed calculation and analysis of parameters such as turn ratio of the fly-back converter,the coil inductance,magnetic core,wire size,is presented in paper based on the model of small signal ac circuits.The analysis and selection for components such as the power switch tube,transformer,filter capacitor,is also made.In order to reduce the influence of the impact voltage of the inductance coil,and as far as possible to reduce the effect of energy dissipation,the detailed comparative analysis of the buffer circuit is carried on.The quasi resonant circuit is selected as the buffer circuit for the fly-back converter.The structure and working principle of constant current control circuit at the core of AP4313 chip is resolved in detail.Finally,in this paper,the experimental monitoring system and the software flow are introduced in detail,and simulation analysis for charging process and equilibrium process for ultra-capacitor group in series with the same initial voltage and different capacity having the same capacity and different initial voltage also made.At the same time,the experiment test for the three monomers of ultra-capacitor group in series is carried on.The result of the experiment test prove the applicability and feasibility for the balancing circuit of ultra-capacitor in series based on fly-back converter.