Second Life Battery Energy Storage System: Modular Interface and Control

The utilization and adaptation of retired batteries has been emerging recently due to the hiking dependance on batteries in electric mobility industry. Hence, piling more retired batteries and presenting urgent need for innovative solutions to mitigate their impact on the environment. As the used batteries are decommissioned out of service at different conditions and different states of health, grouping them into one application is not trivial. Each battery bank is dealt with as independent source and requires separate interface. The control of retired batteries is more challenging in the sense they have variable charging/discharging characteristics as compared to new batteries, different nominal voltages and residual capacities. This paper presents a distributed power electronic interface that can be used with multiple retried batteries to feed common dc link. Each battery power electronic converter is current controlled while single dc link voltage loop is implemented. The currents references for each converter are derived from the single dc link voltage loop through proposed current sharing mechanism that guarantees the batteries are discharged at different rates such that they are depleted at the same time to maximize the utilization time of the batteries. Proposed topology, control structure and simulation results are presented and verified.