A multilevel-multiphase DC-DC converter for use in battery-supercapacitor hybrid energy storage systems

Abstract

With the increasing interest of electric vehicles as a form of clean transportation, automotive manufacturers are pushing to release attractive electric vehicle models for consumers. The main limitation for electric vehicle development, is developing a battery with high energy density as well as a high power density without sacrificing the cycle life of the battery. One of the proposed solutions is using a hybrid energy storage system, which combines an energy storage device with a high power density, such as a supercapacitor, along with one with a high energy density, such as a lithium ion battery. This combination creates a more ideal energy storage system for use in electric vehicles, improving the batteries cycle life without sacrificing performance or range. This document discusses the supercapacitor hybrid energy storage system and the challenges involved in implementing a practical system, focusing on the DC-DC converter required to connect the supercapacitor to the battery. A novel startup technique and application of the flying capacitor multi-level, multi-phase bi-directional DC-DC converter will be presented and the simulation results of a practical prototype discussed. This includes the design, component selection, startup sequence and programing of the converter.