Offset Compensation Network: Improving the Control of Battery Energy Storage Systems

Recently, battery energy storage systems (BESS) have gained importance due to the growing introduction of intermittent renewable energy power plants. Although BESS already has multiple applications, the current standard approach presents several drawbacks aggravated by the second-life batteries use. In order to deal with this issue, the literature proposes the integration of dc/dc converters in the batteries, an approach known as smart battery. However, due to the different capacities of the batteries, the conventional control of smart battery packs does not guarantee a constant dc-link voltage, because during operation, some dc/dc converters can reach their physical voltage limit. Therefore, this paper proposes an algorithm called offset compensation network (OCN) that guarantees constant dc-link voltage even when there are saturated converters. Simulations in software PLECS and hardware-in-the-loop experiments validate the proposal. The results prove the improvement of the technology as the possibility to operate with fixed dc-link voltage, enabling the use of second-life batteries, OCN algorithm reduces the SOC balancing time in 6.25% and avoids dc-link voltage variations during the balancing process. Finally, this technology is fully compatible with current power conversion systems, allowing an easy retrofit of standard BESS.