IMPACT OF MODULE VOLTAGE ON EFFICIENCY OF BATTERY-INTEGRATED-CONVERTER SYSTEMS

Abstract

The concept of modularizing batteries with multiple dedicated DC-DC or DC-AC converters brings several benefits as compared to a single battery pack and converter. These include charge balancing control, enhanced reliability, improved safety, and lower investment risk. Lower voltage and power ratings of power electronic converter elements may also be beneficial, but require optimization. The system design might favour fewer battery power modules (BPMs) with a high number of battery cells and higher voltage power electronic switches, or many BPMs with fewer cells with low voltage switches. This paper examines the optimization and other practical trade-offs associated with the selection of the voltage rating of battery power modules (BPMs) in a battery-integrated-converter system from an efficiency perspective. A nominal 3.8 kW battery system with LiFePO4 battery cells is taken as an example, and modularized with integrated buck converters for a regulated 380 Vdc bus. Based on MOSFET and thus module voltage rating (30, 40, 60, 80, 100 and 150 V), different configurations are derived. The MOSFET and inductor losses of different configurations are examined for high and low working frequencies. The total system losses of all scenarios does not exceed 52 W, for both high and low working frequencies. However, configurations with a high number of lower voltage modules have the advantage of lower MOSFET loss, which should simplify cooling.