Lithium-ion battery state-of-charge balancing circuit using single resonant converter for electric vehicle applications

Abstract

The series of energy storage devices, namely battery, super/ultra-capacitor string voltage balancing circuit, based on a single LC energy converter, is presented in this paper. It transfers the excess energy directly from the higher cell to the lower cell in the string. This requires n-4 bidirectional MOSFET switches and a single LC tank for n number of energy storage device strings. This active balancing circuit has high efficiency, fast balancing speed, small size, low cost, and maximum energy recovery. All MOSFET switches are operated in a near-zero current system and controlled by complementary plus wide modulation signals in synchronous trigger patterns. It achieves the zero voltage gap between two nonadjacent cells in a series battery or supercapacitor string and works on cyclic charging and discharging conditions. In this circuit, the resonant frequency is the same as the switching frequency, and the resonant frequency is reduced. The details of theoretical analysis and operation principles are provided. The experimental result of two 4200 mAh Li-ion cell states of charge 95 % (3.958 V) and 66 % (3.712 V), respectively, after 79 min, voltage difference becomes zero (0 V). Furthermore, we conduct our experiment on lead–acid battery and super-capacitor. This balancing circuit is stable and suitable for battery management systems in electric vehicles.