Optimal Design of Battery Charging Converters Based on Energy Efficiency

In pursuit of efficient battery charging systems, zero-voltage switching phase shift full bridge (ZVS-PSFB) converter topology has been widely used for medium to high power levels. Also, there are zero-voltage zero-current switching (ZVZCS) techniques that implement secondary side passive auxiliary circuits and reduce the conduction loss in semiconductor devices resulting in better efficiency. However, battery charging is a nonlinear load where the power converter operates from heavy load to light load. In such operations, a power converter can be considered more efficient if it consumes less energy in a charging cycle rather than a high peak efficiency at a particular load. The aim of this paper is to investigate such an approach. The basic phase shift full bridge (PSFB) circuit and two efficiency improvement variants proposed in the literature (ZVZCS-PSFB) are considered for the study. An analytical approach is considered for estimating the losses over a full charging cycle. Rating of the battery charger considered is 40V-130V, 5kW. The study confirms the premise that higher efficiencies in certain load conditions is not a sufficient consideration in the design of battery charging converters. Simulation study is carried out in MATLAB/Simulink environment.