Implementation Of Multilevel Battery Charging Scheme For Lithium-ion Batteries

Fast and efficient battery charging is a necessity for battery driven automobiles. This paper presents a multilevel charging technique for Li-ion batteries used in electric vehicle application. Five constant current levels are used instead of conventional single constant current level for fast charging of the battery. A DC-DC converter as a current source is employed in the charging circuit for safe and efficient charging. Accurate estimation of state of charge (SoC) as a feedback is utilized to implement the above optimal battery charging technique. SoC estimation is done with the help of a hybrid method obtained by combining Open Circuit Voltage (OCV) method and coulomb integral method. Estimation of battery parameters is carried out using Simulink Design Optimization (SDO) tool. Simulations are performed using MATLAB 2018a. The error in SoC estimation between inbuilt battery SoC estimation tool and estimation through modified coulomb counting method is found to be within 2%. All the experiments are done with 3.7 V, 1.1 Ah Li-ion battery. Hardware results are presented for conventional and multilevel charging methods. A comparative study demonstrates that Multilevel charging method charges the battery 48.21% faster than the conventional method.