Variable-Gain <i>LLC</i> Converter With Series–Parallel Hybrid Switch-Controlled Capacitor Network

In this article, a variable-gain <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter with a series–parallel hybrid switch-controlled capacitor network is proposed. By tuning the duty cycle of two controlled switches, the resonant capacitance of converter can be regulated and will slightly shift the parameters of resonant tank. Meanwhile, the added switches will be turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> at the zero-crossing point of resonant current to guarantee soft switching. Besides, a mode switching scheme based on the modulation of both switching frequency and capacitance is proposed, by which a group of converter voltage gain curves can be obtained and consequently expands its operation range. In order to verify the effectiveness of the proposed design, a 250 W prototype converter is designed and tested under different loads and modes. It shows that the proposed design can retain the characteristics of conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter, such as soft switching and high efficiency, while it can achieve a wider range of input voltage and a robust control of output voltage against disturbances from input voltage.