A Wide Output Voltage Range LLC Resonant Converter Based on Topology Reconfiguration Method

This article proposes a wide output voltage range LLC resonant converter based on topology reconfiguration method (TRM). First, with different driving signals two operational modes of inverter circuit and rectifier circuit of the proposed topology are analyzed, respectively. On this basis, the converter in whole voltage range has three variable operating modes considering voltage gain by different combination between two kinds of inverting modes and two kinds of rectifying modes. Thus, compared with conventional LLC converter, the voltage gain range can be extended by four times within the same switching frequency range using TRM plus pulse-frequency modulation (PFM). Comprehensive analysis of circuit states and soft-switching conditions in these three modes are presented. Moreover, the design of voltage area division in three modes is discussed to arrive a better tradeoff between efficiency and power density. A design flowchart is given to help to implement an efficiency optimization algorithm. In addition, a smooth mode transition technique is proposed to avoid the rapid frequency change during reconfiguring modulation strategy. Finally, a 2 kW 100-900 V output prototype is built, and main experimental results are provided to verify the effectiveness of the proposed topology and TRM.