Experimental Analysis and Simulation of Mixed Storage with Lithium-Ion Batteries and Supercapacitors for a PHEV

This work focuses on the simulation and testing of an innovative storage system for a PHEV vehicle, investigating the possibility of replacing the car's original storage system with a mixed-storage system with lithium-ion batteries and supercapacitors connected in direct parallel without the use of an intermediate DC/DC converter. The aim is to evaluate the behavior of the supercapacitors' branch compared with that of the Li-ion cells, both in the discharge/charge transients and over an entire WLTP cycle (Worldwide harmonized Light vehicles Test Procedure). The analysis started with the definition of the digital models of a lithium cell and a supercapacitor. The parameters of the models were tuned through experimental characterization of the two storage cells, Li-ion and supercapacitor. Subsequently, the overall models of the branch with the lithium cells and the branch with the supercapacitors were constructed and connected. The overall storage system was sized for application to a PHEV, and a reduced-scale storage system was realized and tested. Finally, the results obtained from the simulations were validated and compared with experimental tests.