Three-Stage Precise Converter in EV Charging-Discharging-Storage Integration Station

Abstract

Converter in EV (electric vehicle) charging-discharging-storage integration station must satisfy the correlation objects. These include: lower harmonic and higher energy conversion efficiency, benefits to battery life, adaption to different batteries, and adjustable charging current. In this paper, we propose a three-stage circuit topology, based on precise charging control, which is able to accomplish these goals on a lithium ion polymer battery pack. It is expected that the converter will also work well on other battery chemistries. In order to use three-stage converter to charge precisely, we need to first design each stage circuit and control strategy. The final strategy can accurately capture the voltage of each DC bus and the charging current of a cell. We also give the analysis of factors affecting battery life and energy conversion efficiency, whereby the three-stage converter is in practice. Comparing with charging simulations of batteries in conventional converter, those in three-stage converter are conducted. Results are presented that that it is possible to achieve more precise charging in integrality of battery charging and extension of battery life than the conventional converter expected in an implementation.