Hybrid Control Strategy for Single-Stage Interleaved Totem-Pole <i>LLC</i> AC–DC Converter With Input and Output Power Decoupling

Abstract

This paper proposes a hybrid control strategy for single-stage interleaved totem-pole LLC AC-DC converter. Since the totem-pole power factor correction (PFC) front-cell provides bi-direction inductor current, this converter is restricted by operating in continuous conduction mode (CCM) or critical conduction mode (CRM). The traditional control strategy shows variable duty cycle of the resonant tank voltage to the instantaneous AC input voltage. Therefore, the line-frequency variation from the AC input-end will be easily interfaced to the load, and brings a large fluctuation of output voltage. To tackle this issue, this paper proposed a novel control strategy that utilizes pulse width modulation (PWM) to shape the input current, and pulse frequency modulation (PFM) to regulate the output voltage. As a positive consequence, the large output voltage ripple brought by the variation of duty cycle for traditional PWM-based control is therefore effectively compensated by the variation of switching frequency, and the power decoupling between the AC pulse input power and constant DC output power is achieved. Numerical-based calculation method is utilized to develop the time-domain analysis of the converter, and a 500W/150V experimental prototype has been built to verify the proposed control strategy and theoretical analysis.