A Fast Simulation Model for Large Scale Battery Packs Used in Heavy Electric Vehicles

Abstract

Voltage imbalance occurs in a battery pack due to the differences of internal resistance, temperature, self discharge rate, leakage current etc. reduce the usable energy over time. To overcome voltage imbalances in the battery pack, cell balancing methodologies are used. Although passive balancing methods provide cheap solutions for equalizing imbalances, active balancing methods make it possible to balance faster. This paper presents an active balancing topology for large scale battery packs in a heavy electric vehicle. In order to investigate the performance of the system, a battery pack and bidirectional flyback converter (BiFLC) based active balancing circuit equipped with switch matrix (SwM) has been simulated by using MATLAB/Simulink. A charge transfer bus, which is supplied by the first cell of the battery pack, is used to transfer energy between the source/ destination cells. Thus, the need for the auxiliary circuit/battery is eliminated. A large scale battery pack consist of 176 series cells and 22 BiFLCs is used in the simulation model. Because of using switching models of BiFLCs requires high run time and more complexity, a simple model of BiFLC using current sources is presented.