Research On Active Voltage Equalization System For Supercapacitors

With the development of automobile industry and the popularization of automobile use,it brings great convenience to people’s travel.At the same time,the energy crisis and pollution emission caused by the large-scale use of traditional internal combustion engine have attracted more and more attention.In recent years,new energy vehicles continue to make breakthroughs in technology,and under the stimulus of policy subsidies,their production and sales are growing steadily,which has become the main direction of the development of the automobile industry.As a new type of energy storage device with the advantages of long cycle life,high power density and short charge/discharge time,supercapacitor is widely used in the field of new energy vehicles.However,due to their own nature,the rated voltage of a single supercapacitor is very low,rarely exceeding 3V.Therefore,in practical application,it is generally necessary to connect multiple supercapacitor monomers into modules in series to meet the use requirements.By difference of manufacturing technology,the super capacitor in the capacitance value,internal resistance,self-discharge rate,capacity attenuation rate on parameters such as inevitable inconsistencies,lead to the monomer voltage change when tandem charge/discharge rate are not synchronized,causing each monomer voltage imbalance in the module,ultimately affect the service life of the super capacitor and efficiency.Therefore,in order to avoid the inconsistency of monomer voltage,it is of great guiding significance to study the voltage balance method of supercapacitor.In this paper,the flying capacitance equalization topology is taken as the research object,and the following studies are carried out:(1)Simplify the equalization topology of the flying capacitor between any monomer.According to the simplified circuit,the equation of equalization efficiency in a single equalization period is deduced.It is found that the equalization efficiency is only related to the voltage of two cells,and the smaller the pressure difference between two cells,the higher the equalization efficiency is.Therefore,based on the equilibrium strategy of monomer with maximum pressure difference,an equilibrium strategy of monomer with non-maximum pressure difference is proposed.(2)In order to verify the hypothesis of the superiority of the proposed equilibrium strategy,a co-simulation is conducted.Based on the simulation results,it is verified that the equalization strategy between the non-maximum differential pressure monomer can further improve the equalization rate.By analyzing the equilibrium voltage variation curve,it is found that the equilibrium strategy between the monomers with non-maximum pressure difference can avoid the frequent low voltage difference between the two monomers during the equalization,and alleviate the problem of too slow equalization rate caused by the late equalization.Considering that the equalization rate is also affected by the distribution of individual voltages,the equalization simulation of different initial voltages is carried out.The simulation results show that the probability of shorter equalization time is 98.5%.(3)Build an experimental platform and compare the results of the two balancing strategies.The experimental results show that the proposed equilibrium strategy has better equilibrium effect,the equilibrium time is shortened by 12.9% and the equilibrium efficiency is improved by 1.7%.