Fundamental Harmonic Amplitude-Frequency Hybrid Modulation Strategy for Half-Bridge LLC Resonant Converters

Inrush current during start-up transient is a special challenge for half-bridge LLC resonant converters, especially when bulk capacitors are connected to the output of the converter. For the half-bridge LLC resonant converter, we propose a fundamental harmonic amplitude-frequency hybrid modulation strategy, so that the output voltage can be regulated continuously from zero to the normal output voltage. By adopting the proposed bipolar and unipolar pulse width modulation strategies, the amplitude of the fundamental harmonic voltage of the primary side of the converter is regulated, allowing the normalized gain of the converter to be continuously adjusted from 0 to 1. In combination with the pulse frequency modulation, the output voltage can be regulated over a wide range. The fundamental harmonic amplitude-frequency hybrid modulation strategy for half-bridge LLC resonant converters is analyzed, including its principle, characteristics, and implementation. The feasibility and effectiveness of the proposed method has been verified based on the experimental results.