A High Efficiency Δ-Lr-Y Type Three-Phase Interleaved LLC Converter With Less Transformer Loss

Abstract

Y-type three-phase interleaved LLC has advantages in high-power applications with small output current ripple. However, the traditional Y-type three-phase interleaved LLC has large winding current under low output voltage and high power (LVHP) applications, which affects the efficiency and power density. In this paper, a high efficiency delta-type three-phase interleaved LLC topology with less transformer losses was proposed. This paper verifies that the transformer loss of the proposed topology is lower than that of the traditional Y-type topology based on the loss model and simulation. Furthermore, considering the coupling between three-phase transformers, a more accurate soft-switching analysis method and the first harmonic gain formula of the proposed topology are given. According to the analysis results, compared with the traditional Y-type topology, only half of the magnetizing current was needed to achieve soft-switching. Meanwhile, the length of the transformer air gap is one-third of the traditional Y-type topology, which can reduce the fringing loss. Finally, a 3 kW prototype was designed and verified. Compared with the Y-type, this paper achieves 19.2% loss reduction.