Design and Control Method of a Battery/Ultra-Capacitor Energy Storage System for EVs

Abstract

This paper presents a battery/ultra-capacitor (UC) energy storage system for the operation of permanent magnet synchronous motor drives in electric vehicles (EVs). In this system, when the EV is used for accelerated operation, the battery provides a stable voltage to the inverter through the DC-DC converter. At the same time, the battery and UC jointly release energy to the inverter to share the larger current demand of the EV motor. In constant speed operation, the battery supplies energy to the inverter through a shunt diode to avoid additional power losses while the DC-DC converter is operating. During the regenerative braking mode, the current produced by the EV motor is charged to the UC to reduce pulse currents flowing into the battery, which may shorten battery life. To validate the effectiveness of the circuit design, several operation scenarios including buck and boot voltage conversion for the operation of proposed battery/UC ESS were examined in the experimental studies. Test results consolidates the feasibility and practicality of the circuit method for the EV applications.