Multiple Operation Modes Based Stacked Structure LLC Converter for Very Wide Range Operation

Great challenges have been posed to conventional frequency-controlled resonant converter in wide range applications. In this paper, the stacked structure inverter with three different modes is applied for resonant converter and two different modulation strategies are applied. Three operation modes, namely, half-bridge (HB), quarter-bridge (QB), and three level (TL) operation mode, are adopted for the stacked structure. For high voltage gain operation (HVG), the HB operation mode and the pulse frequency modulation (PFM) are adopted; for medium voltage gain operation (MVG), the TL operation mode and pulse width modulation (PWM) are adopted; for low voltage gain operation (LVG), the QB operation mode and PFM control strategy are adopted. By designing the range for each mode, the proposed converter is superior over the traditional converter from the perspectives of efficiency and power density.