Wide-Range Voltage Gain and High-Efficiency of Isolated LLC Converter using Six-Switch and Two Asymmetric Transformers

摘要

This paper proposes a circuit configuration of LLC converter a wide voltage range and high efficiency. The proposed LLC overcomes the narrow voltage gain range of conventional full-bridge (FB) LLC converters. Owing to the switching patterns of the primary side, two resonant tanks operate in half-bridge and FB modes. The two resonant tanks are designed with different parameters, and the proposed LLC has six operating modes. These modes enable a squeezed switching frequency span, which is close to the resonance frequency. The proposed control method achieves seamless transition between the operating modes and a wide voltage gain range. First, the operating principles and characteristics of the proposed converter are analyzed. The transitions between modes are determined based on the analyzed theory. In addition, the design guidelines for the two resonant tanks are describe. The parameters of the two resonant tanks are designed using the first harmonic approximation method, and each is determined to achieve a wide voltage range and high efficiency. A prototype rated to 1.0-kW is designed to convert the input of 360V to an output of 100-420V, and the proof of concept is validated. Experimental results confirm that the proposed circuit achieves a voltage gain of less than 0.5 to more than 2.0 under different load conditions. Furthermore, the proposed mode transition method achieves seamless transition between modes without complicated calculations. Experiments confirm a maximum efficiency of 96.5%.