A fuzzy control constant polarisation voltage charging method for lithium-ion batteries

Electric car is the future development trend of the automobile industry. Currently, the electric car's energy storage components are mainly batteries. Various types of, batteries have been studied for many years, compared with traditional lead-acid and nickel-cadmium batteries, lithium-ion battery has the advantage of high energy ratio, long life, low pollution and high operating voltage characteristics. The polarisation during charging is the main factor affecting the fast charging efficiency of lithium-ion batteries. Although the current charging method for lithium-ion batteries is faster, the methods of improving the charging efficiency and prolonging the life by controlling the polarisation of the battery need to be further improved. Therefore, in this paper an alternate fast charging technology which can maintain constant polarisation voltage is proposed. Based on the traditional lithium battery RC equivalent circuit model，the charging process of lithium battery is simulated. The charging current, the initial state-of-charge (SOC), the initial polarisation state, the cycle life and other aspects are analysed. The relationship between the polarisation voltage and SOC is established. The polarisation voltage is divided into different sections, and it is controlled within constant threshold value. On the basis of this study, the fuzzy control algorithm is used to control the charging polarisation voltage to optimise the fast charging of the battery, so that the charging current can adapt to the SOC rechargeable current of the lithium-ion battery at any time. The experimental results show that compared with the traditional constant-current constant-voltage charging(CC-CV) method, the proposed constant polarisation charging method can greatly shorten the charging time by about 20% and therefore the charging efficiency is improved, while there is no obvious difference in temperature rise.