Tutorial Session I

Khai D. T. Ngo, Chair
Sunday, April 9, 2017

High Efficiency High Density Bi-Directional Battery Charger with Integrated Magnetic Components

Qiang Li

Plug-in electric vehicles (PEV) have drawn more and more attention in recent years. One crucial challenge for PEV’s commercialization is the demand of lightweight, compact, and efficient on-board charger system. The state-of-the-art level-2 on-board charger products are majorly Si-based, which operate at less than 100 kHz switching frequency, and has only 3~12 W/in3 power density and at most 92~94% efficiency.

Recently CPES developed a two-stage bi-directional on board charger structure with WBG) semiconductor devices. The first stage is a two-phase interleaved Totem-Pole ac/dc working at critical conduction mode with 300kHz switching frequency per phase. All the fast switches can achieve zero voltage switching (ZVS), resulting small switching loss. The second stage is a CLLC resonant converter featuring symmetrical resonant tank. ZVS is also achieved and the switching frequency is pushed to 500kHz. In order to deal with the wide battery voltage range, a variable DC-link voltage structure is proposed. By allowing the DC-link voltage tracking the battery voltage, the gain range of the resonant converter is reduced significantly. Therefore, the switching frequency range is kept narrow and the best efficiency is maintained within the entire battery voltage range. In addition, all the magnetic components are implemented using PCB winding, including transformer and inductor for the resonant converter and the coupled inductor for the PFC stage. As a result, manufacture automation and good parasitic control can be achieved. A 6.6kW bi-directional on-board charger is demonstrated with 96% efficiency over the entire battery voltage range and 37W/in3 power density, which is far beyond the current industry practice.

This presentation will talk about the detailed design of this high frequency WBG based bi-directional on-board charger, which includes system architecture evaluation, high frequency digital control for both ac/dc and dc/dc stage, design of PCB integrated transformer and inductor, and common mode EMI noise reduction based on balance concept.