Balance discharging for series-connected batteries

Charge equalization during the charging process has been extensively discussed for a series-connected battery bank. However, charge inequality may happen to batteries as well during discharging. Unbalanced discharging can be critical for the application of a series-connected battery bank but was seldom mentioned. The imbalance among batteries may result in over-discharging and consequently damages the batteries. To solve the problem of charge equalization, a balance discharging method for series-connected battery bank is proposed. The balance discharging is performed by an output converter which provides output voltage regulation. In addition, the inapplicable batteries are isolated in case that they are exhausted or damaged. The balance discharging method is realized by a fly-back conversion circuit with a multi-input transformer. A simple PWM (pulse-width-modulation) controller is implemented to perform the control tasks. The applicability of the proposed method is confirmed by experiments.