PWM–PFM Hybrid Control of Three-Port LLC Resonant Converter for DC Microgrids

Yi Zhang (), Xiangjie Liu, Jiamian Wang, Baojiang Wu, Feilong Liu and Junfeng Xie
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Yi Zhang: The State Key Laboratory of Alternate Electrical Power Systems with Renewable Energy Sources, North China Electric Power University, Beijing 102210, China
Xiangjie Liu: The State Key Laboratory of Alternate Electrical Power Systems with Renewable Energy Sources, North China Electric Power University, Beijing 102210, China
Jiamian Wang: Hebei Wind-Photovoltaic-Hydrogen-Storage System Security Monitoring and Intelligent Operation Center of Technology Innovation, North China University of Science and Technology, Tangshan 063210, China
Baojiang Wu: Hebei Wind-Photovoltaic-Hydrogen-Storage System Security Monitoring and Intelligent Operation Center of Technology Innovation, North China University of Science and Technology, Tangshan 063210, China
Feilong Liu: Hebei Wind-Photovoltaic-Hydrogen-Storage System Security Monitoring and Intelligent Operation Center of Technology Innovation, North China University of Science and Technology, Tangshan 063210, China
Junfeng Xie: Hebei Wind-Photovoltaic-Hydrogen-Storage System Security Monitoring and Intelligent Operation Center of Technology Innovation, North China University of Science and Technology, Tangshan 063210, China

Energies, 2025, vol. 18, issue 10, 1-25

Abstract: This article proposes a high-efficiency isolated three-port resonant converter for DC microgrids, combining a dual active bridge (DAB)–LLC topology with hybrid Pulse Width Modulat-Pulse Frequency Modulation (PWM-PFM) phase shift control. Specifically, the integration of a dual active bridge and LLC resonant structure with interleaved buck/boost stages eliminates cascaded conversion losses. Energy flows bidirectionally between ports via zero-voltage switching, achieving a 97.2% efficiency across 150–300 V input ranges, which is a 15% improvement over conventional cascaded designs. Also, an improved PWM-PFM shift control scheme dynamically allocates power between ports without altering switching frequency. By decoupling power regulation and leveraging resonant tank optimization, this strategy reduces control complexity while maintaining a ±2.5% voltage ripple under 20% load transients. Additionally, a switch-controlled capacitor network and frequency tuning enable resonant parameter adjustment, achieving a 1:2 voltage gain range without auxiliary circuits. It reduces cost penalties compared to dual-transformer solutions, making the topology viable for heterogeneous DC microgrids. Based on a detailed theoretical analysis, simulation and experimental results verify the effectiveness of the proposed concept.

Keywords: PWM-PFM hybrid control strategy; three port; LLC resonant; ZVS (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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