SOH Based Power Sharing Algorithm for Second-life Batteries Using Health Factors

The uncertain capacity differences in second-life batteries due to internal characteristics require SOH balancing for SLB modules. The most popular SOC balancing does not guarantee the SOH balance and battery efficiency. Many works of literature try to extract the SOH parameter through either the number of cycles or DOD change. Still, current rate and temperature also have significant influence over the SOH parameter. To solve this problem, in this article the SOH is derived from the most effective health degradation parameters based on DOD and charge rate. An online SOH estimation method is proposed, and according to the determined SOHs, a power-sharing control algorithm is developed to realize the SOH balancing. This article employs the conventional battery energy storage system (BESS) as the second-life battery module since most EVs utilize the bi-directional DC-DC converter boost-buck configuration. MATLAB simulation and floating-point DSP controller hardware-in-loop (CHIL) experimentation results are presented for discharging, DC bus voltage variation and change in power demand cases to verify the proposed algorithm. The algorithm performs decent power-sharing according to their SOH values based on DOD and current rates.