Series battery equalization using sequential difference algorithm

Batteries are most widely used device to store the energy. The importance of the batteries is increasing especially to store the energy harnessed from renewable energy resources. The application of batteries in hybrid electric vehicles (HEV) is ever demanding and increasing. The batteries when employed in stack, individual cell parameters will be altered due to the effects of temperature gradients, ageing effects and charging and discharging cycles. Individual cells will have different SOC. If the stack is considered as a two terminal device and allowed to charge, the individual cells in the stack will not be charged uniformly. Few cells will be overcharged, few will be undercharged and few will be at the mid-range of its maximum value. Continued use of stack with this condition will degrade the life of the batteries and the efficiency of the entire system drops to unacceptable range. High-end battery users are aware of the uniformity to be achieved in the battery stack specially considering the valve regulated lead acid batteries. The paper aims at having the equalization for series connected lead acid batteries. The paper presents a simple and efficient active equalization scheme to equalize the batteries connected in series. The implemented model checks the voltage value across each battery and identifies the battery with the weakest voltage. The identified battery is allowed to charge without affecting the charging needs of other batteries in the stack. The paper is to have a firsthand experience in equalizing the series connected batteries.