PASSIVE CELL BALANCING AND ANALYSIS OF LLC CONVERTER WITH BUCK CONVERTER FOR BATTERY CHARGING USING CCCV TOPOLOGY

Abstract

This Project presents the passive cell balancing of a lithium-ion battery cells and battery cell charging with the use CCCV (Constant current constant voltage Topology). When battery cells are connected in series, they frequently become unbalanced. The cell voltages aren't all the same. Variations in cell parameters such as cell difference in SOC of battery cell, impedances, capacity, self-discharge rate, cell temperature and so on can cause this unbalance. Passive cell balancing is constructed and examined in a stand-alone state in this paper. The features of passive balancing are determined in this study by conducting an on-line passive balancing experiment of charge and discharge at various capacities (SOC). In this Project, circuitry for battery charge controller circuit is also designed and the Constant voltage/constant current (CCCV) topology is investigated to prevent overcharging issues. Passive Balance method for Battery charging using CCCV topology is not effective due to power wastage so I used Cascaded system of LLC resonant converter with Buck converter for CCCV charging because LLC resonant converters are used in various sectors due to their advantages of high efficiency, high energy density, electrical isolation, low electromagnetic interference (EMI), wide output ranges and high frequency. A Good power factor for the LLC resonant tank is required to achieve high efficiency over a wide input voltage range. A unity voltage gain can be accomplished over the whole loading conditions by having switching frequency equal to resonant tank frequency in LLC converter, however it is not suited for constant current – constant voltage (CC-CV) battery applications. The use of a buck converter at the output of an LLC resonant converter to regulate the charging current and voltage for battery charging applications is also proposed in this Project. The use of a buck converter allows the output voltage of the LLC converter to be varied, ensuring CCCV charging. This project is designed CC-CV charging for 48V/40Ah Battery. The proposed system is analysed and studied in MATLAB/Simulink.