Design Of The Wireless Charging And Balancing System For The Series-Connected Battery Pack

Lithium-ion batteries are widely used in unmanned aerial vehicles,mobile electronic devices and electric vehicles because of their high power density,low self-discharge rate and long operation life.In the above applications,lithium-ion batteries are usually connected in series to form a battery pack aiming to satisfy the power and voltage demands.However,the internal resistance,capacity and voltage of single battery may be inconsistent due to the manufacturing process,which limits the available capacity and output power of the battery pack,shortening the operation life and endangering the safety of the battery pack.In some special applications that require high quality tightness,charging safety and consistency of the battery pack should be considered using wireless power transfer technology considering charging and balancing for the battery pack.To solve the above problems,this paper proposes a wireless charging and balancing system for the series-connected battery pack,which uses a set of magnetic coupler to realize the dual functions of battery wireless charging and single battery wireless balancing.The system can not only satisfy the charging demand of the battery pack,but also solve the problem of battery pack available capacity degeneration caused by state of charge(SOC)inconsistency,so as to prolong the operation life of the battery pack.The main contents of this paper include:Firstly,the mutual inductance coupling theory is used to analyze the principle of magnetic coupling resonance wireless charging.By comparing the transmission characteristics of four basic compensation circuits,the series-series(SS)compensation circuit is used in this paper.Further,the influence of load resistance,coupling coefficient and frequency variation is analyzed by using the control variable method,which improves the theoretical basis for the hardware design of the system.Secondly,aiming at the problems of long balancing time and low available capacity of the battery pack,a balancing control strategy based on genetic algorithm is proposed to optimize the available capacity and balancing time of the battery pack based on SOC.Thirdly,the primary and secondary circuits of the system are designed considering the charging and balancing requirements of the battery pack,including principle analysis of circuit and device selection.Further,the conductor,coil and magnetic core of the magnetic coupler are designed respectively.Finally,an experimental platform is built to verify the designed wireless charging and balancing system for 7-cell series-connected battery pack.The experimental results show that the designed system realizes the 1C(2.5A)wireless charging of 7-cell battery pack and the 1C wireless balancing of any single battery in the battery pack.The proposed balancing control strategy increases the available capacity of the battery pack by 31.03%,and the balancing time is reduced by 17.54% compared with the SOC consistent balancing method.