A Fixed‐Frequency Hybrid‐Controlled Secondary‐Side Semi‐Active Resonant Converter With a Wide Gain Range

ABSTRACT To address the challenge of wide‐range output regulation in LLC resonant converters, this paper proposes a novel hybrid control strategy. By replacing only two diodes on the secondary side with MOSFETs, without increasing the number of resonant elements, the converter achieves a wide voltage output range of 175 to 450 V. The hybrid control strategy primarily employs the secondary side semi‐active (SSSA) control method, combined with variable bus voltage (VBV) control and primary side phase shift (PSPS) control method, ensuring that the converter always operates at the resonant frequency. This approach enables high conversion efficiency and soft switching of all MOSFETs. Additionally, the area equivalence principle is utilized to derive exact expressions for the resonant current and converter gain in the SSSA mode, simplifying the converter design process. An experimental prototype was designed and tested, demonstrating the feasibility of the proposed control strategy with an input voltage range of 300 to 400 V, an output voltage range of 175 to 450 V, and a rated power of 6.6 kW. The prototype achieved a maximum conversion efficiency of 97.8%.