Study On Variable Frequency Pulse Fast Charging Technique For Li-ion Battery

Hazy weather occurs frequently in China, which leads to the community focus on vehicle exhaust emissions. The electric car as a green, economical transportation means is widely used. Battery as a power source of electric vehicles, its own performance and charge-discharge characteristics has an important influence on the development and use of electric vehicles.Lithium-ion batteries are the most potential secondary batteries now, with which the efficient and safe battery fast charging strategy is researched implemented in the present study. Typical rapid charging methods, which have preferably achieved the purpose of rapid charging, but it remains to be further improved in the relations of coordinating charging efficiency and eliminating polarization. This paper combines the advantages of variable frequency pulse charging method with negative pulse depolarization ideas, makes full use of fuzzy control technology, which polarization effects can be mitigated to some extent, thus making the charging speed accelerated and the charging effect improved.The main research contents are as follows:1. This paper selects the lithium-ion battery as the research object, then analyzes its working principle, the charge and discharge characteristics and influencing factors, researches the mechanism of polarization, eliminating methods and principles.2. Analysis the advantages and disadvantages of the existing fast charging methods, and the difficulties in realizing high current charging to enhance the charging efficiency, this paper focused on the analysis of the pulse charging method, then introduced the principle of variable frequency fast charging method, which using perturbation and observation method to detect and dynamically track the optimal frequency during different charging step, so as to the maximum current, which the optimal frequency corresponds to, can be provided to charge the battery.3. Research on the question that the effect of depolarization is not obvious, this paper implement the fuzzy controller 1 to determine the degree of polarization, which means giving the negative pulse at a proper time and the fuzzy controller 2 for giving degree of depolarization, making the battery charging under its gas analysis point voltage. Finally, by contrast test to verify the effectiveness of the designed variable frequency charging system that based on fuzzy control.4. Designed some hardware circuit and software flow chart of the lithium-ion battery variable frequency fast charging system, and through building lithium-ion battery testing platform, tested the function of fast charging system.Research for this article, is suitable for portable electronic devices, electric vehicles, uninterruptible power systems that using powered batteries as energy storage devices.