A Simple Modulation Strategy for Full ZVS of Single-Stage Electrolytic Capacitor-Less EV Charger with Universal Input

The single-stage electrolytic capacitor-less on-board charger (OBC) is attracting attention with the possibility of achieving high efficiency, high power density, and low component count. However, under universal input and wide battery voltage, the single-stage OBC has a difficulty in achieving ZVS turn-on while maintaining unity power factor. In order to achieve ZVS under wide voltage range, the conventional single-stage OBC uses multiple control variables including switching frequency where the switching frequency usually varies widely, which complicates the converter design and optimization. In this regard, a totem-pole based single-stage electrolytic capacitor-less OBC was introduced in [36]. It uses one control variable and fixed switching frequency. However, this topology is not able to achieve full ZVS under wide voltage range and has high grid current total harmonic distortion (THD). This article proposes a simple modulation strategy that uses an adaptive duty-cycle and phase-shift modulation to achieve full ZVS under universal input and wide battery voltage. In addition, the fourth-harmonic injection method greatly reduces the grid current THD. The effectiveness of the proposed modulation was validated on a 3.84-kW prototype with 100-240 V ac input and 460-800 V battery voltage. The efficiency is also increased up to 2.3%p under low-voltage grid compared to the previous work.