Research of Equalizing Charge Control Strategy for VRLA Batteries Circuit

In energy storage of stand-alone photovoltaic system,battery string with many cells in series connection can provide higher voltage. But for each cell,any slight voltage difference can be amplified in the charging and discharging cycles. Unbalanced cell voltage in battery string will give rise to serious over-charging or over-discharging,and decrease the total storage capacity and the battery cycle life. Therefore,maintaining cell voltage at an equal charge / discharge level is significant for enhancing the battery cycle life. Aiming at the non dissipative-type equalization circuits,the circuit model of battery equalization charge was studied, and an equalization charge control strategy which can not only achieves quick charge but also increases the battery cycle life was proposed. According to the proposed charge control strategy,a controllable PWM divergence module can automatically realize energy transfer between cells and overcome dissimilarity among all batteries. Experiment shows that high energy transmission efficiency and rapid voltage equalization are achieved,and the battery overcharge or over discharge can be avoided and extend storage battery lifetime.