Investigation of Leakage Inductance in Three-Winding Transformer for Three-Port Integrated Onboard Chargers

Three-port isolated converters play a pivotal role in the simultaneous charging of high voltage (HV) and low voltage (LV) batteries of electric vehicles (EVs). The leakage inductance of the high-frequency transformer significantly influences power transfer of these isolated converters by impacting duty-cycle and output voltage regulation. Higher leakage inductance values lead to increased power loss and less accurate voltage regulation. Moreover, improper leakage inductance values can hinder the soft-switching operation of these converters. Hence, accurate estimation of leakage inductances of the three-winding transformer is important for optimizing the design and performance of these converters. In this paper, the leakage inductances of a three-winding transformer with two distinct winding arrangements are investigated in the context of a novel 3.3 kW three-port integrated onboard charger (IOBC). Both the analytical method and 3-D Finite Element Method (FEM) are considered to evaluate the leakage inductances. By comparing the obtained results, the winding configuration with a lesser leakage inductance set is chosen for the hardware prototype of the three-winding transformer. Furthermore, a series of short-circuit tests is conducted on the experimental prototype. The comparison between experimental and simulation results reveals a maximum error of 3.6%, illustrating the accuracy in estimating leakage inductances for the three-winding transformer.