A Wide Input Range High-Frequency LLC Resonant Converter With Hybrid Control Strategy

This paper aims at designing a high-frequency LLC resonant converter with hybrid control strategy, which achieves a continuous wide input range in a narrow frequency range without auxiliary switches or topology change. In addition, the designed converter can operate in both full bridge and half bridge modes. While in full bridge mode, pulse frequency modulation (PFM), single arm asymmetric pulse width modulation (SA-APWM) and single arm asymmetric pulse width modulation with phase shift modulation (SA-APWM-PSM) are applied to obtain a continuously decreasing gain. In half bridge mode, PFM and asymmetric pulse width modulation (APWM) are adopted to achieve lower gain and adapt to higher voltage input. It was found that the switching between the control methods proposed above is smooth, resulting in good steady-state and dynamic performance of the converter. Based on this hybrid control strategy, a Fourier expansion analysis method is adopted to obtain the analytical equations of zero voltage switch (ZVS). Finally, a 600kHz-1MHz, 330W LLC resonant converter simulation model with 33V to 138V input and 110V output is built to verify the effectiveness of the proposed hybrid control strategy and the ZVS analysis method.