Design Optimization of a Multi-Level Converter Supercapacitor System for Electrochemical Impedance Spectroscopy in EV Fast-Charging Stations

This paper presents a novel design method to optimize the volume of a high-power Electrochemical Impedance Spectroscopy (EIS) add-on system for Electric Vehicle (EV) Direct-Current Fast-Charging (DCFC) stations. The EIS system consists of a Supercapacitor (SC) energy storage system and an 800V bidirectional Flying Capacitor Multi-Level (FCML) dc-dc converter, which are co-designed to minimize the system volume. The contributions of this paper are the deterministic optimization algorithms for 1) SC energy storage systems and 2) dc-dc converters. The SC design algorithm minimizes the number of SC cells while ensuring the system meets the 4kW peak power and worst-case energy requirements for bidirectional power flow by generating dynamic power profiles. The FCML bidirectional dc-dc converter design algorithm optimizes the number of levels and phases, considering various commercially available power devices, component derating, and power losses for the converter. The algorithm generates a design space with optimized combinations of FCML-SC systems, revealing the global optimum design with a volume of 2.1L, which is 4 times smaller than the design employing an off-the-shelf converter and SC system.