Current Equalization Strategy for Three-Phase LLC Converter Based on Integral Phase-Shift Control

With the rapid development of the new energy industry, the demand for high-performance power electronic devices is growing. The three-phase interleaved parallel LLC resonant converter has been widely used due to its characteristics such as high power density, low electromagnetic interference, high efficiency, wide input range, small output current ripple, and low component stress. However, differences in resonant parameters among the modules of the three-phase LLC converter may lead to uneven distribution of load currents. This paper proposes a novel control strategy suitable for the three-phase interleaved parallel LLC converter. The method controls by comparing the relationship between the three-phase resonant currents and adjusting the sizes of two phase-shift angles, thereby influencing the amplitude of the voltage fundamental wave. In this way, the resonant currents of the three phases can be balanced, achieving load current balance in the three-phase LLC converter. Finally, the effectiveness of this integral phase-shifting control strategy is validated through simulation and experimentation.

I. Introduction

As the global natural environment deteriorates, humanity is facing severe crises such as energy shortages and climate warming. To address this issue, countries worldwide have reached a consensus to vigorously develop clean and renewable energy as a common goal. Against this backdrop, new energy vehicles are rapidly emerging due to their advantages such as zero emissions, clean energy, and high energy utilization. Batteries, as the core of new energy vehicles, have their charging equipment's quality directly impacting the electric vehicle's range and lifespan. In this charging equipment, the On-Board Charger (OBC) has become a focal point of research globally [1]. Currently, the common OBCs in the market adopt a two-stage structure of PFC+DC/DC conversion. The frontend PFC corrects the power factor, while the back-end uses DC/DC conversion. In the DC/DC topology, the LLC resonant converter is widely used in OBCs due to its high power density, low electromagnetic interference, high efficiency, and wide input range characteristics[2].