A Capacitor-Isolated Automatic Equalization Charging System Based on OR-Ing Diodes for Series-Connected Cells

Energy storage systems (ESSs) are widely used in diverse fields such as distributed power grids, uninterruptible power supplies (UPS), electric transportation, and electric vehicles (EVs). To meet the high-voltage demands of ESSs, cells are typically connected in series. However, voltage mismatch inevitably arises from cell variations, which can shorten battery lifespan and in severe cases, lead to safety hazards such as fires or explosions. To address this issue, prior-art technologies have been investigated in previous studies. However, they often suffer from complex multiswitch control and bulky magnetic components. Therefore, a capacitor-isolated automatic equalization charging system based on the OR-ing diodes has been proposed. Owing to the characteristics of the OR-ing diodes, the lower (or higher) the cell voltage, the longer (or shorter) the conduction time of the diodes, which results in more (or less) energy gained by the module with lower (higher) cell voltage. In this way, automatic voltage equalization among the battery cells is achieved without the need for any sensors or complex control strategies. An experimental prototype consisting of four series-connected cells was built to validate the balancing performance of this equalization charging system.