A Novel Hybrid PFM/IAPWM Control Strategy and Optimal Design for Single-Stage Interleaved Boost-LLC AC–DC Converter With Quasi-Constant Bus Voltage

Abstract

Single-stage boost-LLC ac-dc converters have been a popular soft-switched topology because of the high-efficiency and being cost-effective. However, low power capacity is its main disadvantage. In this article, a novel single-stage interleaved boost-LLC ac-dc converter with higher power capacity is presented while achieving the low input current ripple. However, it still suffers from the wide and high bus voltage for universal operation, as a result of the conventional pulse frequency modulation (PFM) with the duty cycle of 0.5. Furthermore, this wide bus voltage will bring the difficulties in designing the LLC resonant cell. To solve these issues, a dual-loop feedback control strategy based on PFM/interleaved asymmetric pulsewidth modulation hybrid modulation and power balance based optimal design are proposed. With the proposed control strategy and optimal design, the bus voltage of the studied converter is not only significantly reduced, but also zero voltage switching for the primary switches and zero current switching for the secondary diodes are still maintained. Thus, the higher efficiency can be achieved. Operation principles and control scheme for the studied converter are fully addressed. The optimal design based on power balance principle is also discussed in this article. A 300 W prototype is fabricated to validate the theoretical analysis and optimal design. The experimental results demonstrate the prototype can simultaneously obtain the universal operation with high power factor above 0.98 and the quasi-constant bus voltage below 500 V. The measured peak efficiency is 92.7% under 115 Vac input voltage at full load.