1M. Sc. [Engg.] Student, Electronics and Electrical Engineering, M. S. Ramaiah School of Advanced Studies, Bangalore-560 058
2Asst. Professor, Electronics and Electrical Engineering, M. S. Ramaiah School of Advanced Studies, Bangalore-560 058
Lead-acid batteries are the most commonly chosen power source for many portable applications. Advantages like high energy density, high nominal voltage, less maintenance, and low self discharge rate are the driving force behind this choice. Although they have many advantages lead-acid batteries have not been used in various applications because of the difficulty of using them well and keeping the individual cells balanced in a series-connected battery pack. This provides the motivation to develop a Battery Charging and Cell Balancing (BCCB) with individual cell equalizers and state of charge (SoC) observers. The main purpose of a BCCB is to monitor the cells in a battery pack to ensure proper operation and balance the voltage and charge in the cells in a battery pack in order to maximize the available energy.
A BCCB is developed for a lead-acid battery pack with two cells connected in series. The BCCB monitors individual cell parameters like voltage and current to ensure proper operating conditions. Battery model equations are derived, which serve as a SoC observer, to predict and correct the charge stored in the cell. A novel dissipative equalization scheme is proposed to achieve cell equalization among the series connected cells in terms of both voltage and charge. The circuit schematic for the BCCB is designed and simulated by using Proteus and NI Multisim. The proposed battery management system is implemented in hardware to demonstrate its operation of two batteries with 12V 7.2 Ah.
Experiments conducted using the implemented BCCB show that a charging strategy that includes cell equalization in terms of voltage allows 31% more energy to be stored in the pack than does a simpler strategy that stops charging once the strongest cell in the battery pack reaches the maximum allowable cell voltage. A charging strategy that includes cell equalization in terms of both voltage and stored charge allows 39% more energy. We conclude that the present study has achieved significant improvements in battery charging and cell balancing efficiencies.
Battery Charging, Cell Balancing, Hybrid Electric Vehicle
