A novel PCB winding transformer with controllable leakage integration for a 6.6kW 500kHz high efficiency high density bi-directional on-board charger

Abstract

Printed Circuit Board (PCB) transformer has been widely used in low power applications. Compared with conventional litz-wire transformer, the manufacture process is greatly simplified and the parasitic is much easier to control. However, in high power applications like on-board charger for electric vehicle, no one has ever done it due to the limitation of high winding loss and high multi-layer PCB cost. The emerging wide-band-gap devices provide the opportunity to adopt PCB transformer in high power applications. In addition, the low inductance requirement brought by high frequency also makes it possible to realize magnetic integration in PCB transformer. In this paper, by using a two stage variable DC-link voltage structure, a novel 6-layer only PCB winding transformer structure is proposed for the second stage of the 6.6kW on-board charger, of which leakage inductance is controllable without sacrificing winding loss. A 6.6kW 500kHz prototype with almost 98% efficiency and 130W/in3 power density is built to verify the feasibility of the proposed PCB winding transformer.