Integrating Second Life EV Batteries to a PV based DC System using a Novel Bidirectional Four-Port Converter

Battery energy storage systems (BESS) have become an integral part of the renewable energy system and second life batteries offer a cheaper solution for storage. Electric vehicle (EV) batteries at 70–80 % capacity, which are no longer ideal for mobility applications, can still be used for stationary storage purposes. This creates a market for used batteries, thereby reducing EV costs. In this paper, a novel Four-Port Converter (FPC) capable of integrating second-life batteries of different voltage ratings and capacities with Photo-voltaic (PV) system and DC grid is proposed. The proposed converter consists of five MOSFETs and is capable of controlling charging and discharging of batteries while ensuring Maximum Power Point Tracking (MPPT) operation of PV. The MPPT for PV is implemented using Perturb and Observe (P&O) algorithm. The analysis of the FPC is given and the control strategy for charging, discharging and MPPT modes are validated through simulation in MATLAB/Simulink.