PFM-PS Hybrid Control Strategy CLLC Resonant Converter Research

CLLC resonant converter has the advantages of high power density, large voltage regulation range, soft switching and bi-directional energy transfer, etc. It is widely studied and used in renewable energy power generation and its energy storage system, new energy vehicles and other fields. The use of conventional control methods has the disadvantage of a wide range of switching frequency variation and a narrow range of soft-switching implementation, which leads to limited efficiency and power density improvement of CLLC converters. The frequency-shift segmentation control can reduce the switching frequency variation range, but it increases the circuit cost and wiring complexity. To solve the above problems, we propose a Pulse Frequency Modulation-Phase Shift hybrid control strategy. This strategy can realize the synchronous adjustment of switching frequency and phase shift angle, which narrows the variation range of switching frequency and helps CLLC converters to improve power density and efficiency. Compared with the segmented hybrid control strategy, the wiring is simpler and the economy is good. The voltage gain and soft-switching realization conditions of CLLC resonant converter are analyzed by First Harmonic Approximation, and the experimental model of circuit simulation with 350V~450V input and 48V/800W output is established for verification, and the correctness of the theoretical analysis is verified.