Advanced Operation and Control Schemes of Retired Batteries in DC Microgrid for Secondary Usage

The utilization of repurposed second-life batteries from electric vehicles in DC microgrids presents a sustainable and cost-effective solution. However, efficiently integrating these batteries within DC microgrids poses two main challenges: (1) poor consistency among retired battery packs; (2) fluctuations in the DC bus voltage. Traditional approaches primarily focus on achieving the state of charge (SOC) balancing within retired battery packs, often neglecting the suppression of voltage fluctuations, thereby compromising system stability. To address these challenges, this paper proposes a virtual DC machine (VDCM)-based control strategy that enhances both the power quality of the DC microgrid and the consistency of retired battery packs. On the one hand, reconfigurable topology and SOC balancing strategies are developed to manage the equalization current, achieving SOC balancing within the retired battery packs. On the other hand, a VDCM strategy is designed to leverage the capacity characteristics of retired batteries to increase the inertia of the DC microgrid. Compared to conventional methods, experimental results show that the proposed strategy not only maintains SOC balancing during both the charging and discharging phases but also significantly reduces overshoot and settle times of dc voltage to 64.2% and 55.6%, respectively.