Design and Control of an Electrolytic Capacitorless Three-Phase On-Board Charger Based on Active Third-Harmonic Current Injection

On-board chargers (OBCs) with conventional two-stage architecture, consisting of an active front-end (AFE) converter and an isolated dc-dc stage, require bulky line filters and dc-link capacitors, resulting in low volumetric efficiency. Active third-harmonic injection and current unfolding methods offer significant improvement in terms of efficiency and power density in power factor correction (PFC) applications. However, existing unfolding-based topologies require two isolated dc-dc converters capable of handling the rated power for PFC and output voltage regulation. This article presents a three-phase ac-dc converter with a third-harmonic current injection circuit that processes a fraction of the total power and a single isolated dc-dc converter for galvanic isolation. Line frequency switching in the rectifier produces varying dc-link voltages, eliminating the requirement of bulky electrolytic capacitors. The article discusses detailed operation and design procedures along with an elaborate comparative analysis between the proposed topology and the conventional two-stage and Swiss rectifier-based isolated topologies. A 6.6 kW prototype is developed and tested for experimental validation of the system in both balanced and unbalanced grid conditions. The experimental results demonstrate unity power factor (upf) operation throughout the operating range, achieving a peak efficiency above 97%.