Wide-Input Series Half-Bridge LLC Resonant Converter and Its Control Strategy
Conventional full-bridge and half-bridge LLC converters suffer from narrow input voltage gain ranges and elevated switch voltage stress, limiting their deployment in photovoltaic, wind, and electric vehicle DC-DC interfaces where source voltage fluctuates widely. This paper proposes a wide-input series half-bridge LLC resonant converter that halves the switch voltage stress via a stacked input capacitor architecture. Two operating modes are analyzed: a high-gain (HG) mode for input voltages above a threshold Vin,th, and a low-gain (LG) mode employing frequency doubling for input voltages below Vin,th. A PSM-PWM-PFM hybrid control method enables stable mode transitions, while a PSM-PWM hybrid voltage-balancing control compensates for input capacitor voltage imbalance. A 600 W prototype operating over a 100-400 V input range validates the theoretical analysis and control feasibility. The converter maintains a narrow resonant network frequency range across the full input span, simplifying magnetic component design and preserving soft-switching characteristics. Experimental results confirm zero-voltage switching (ZVS) for primary switches, balanced input capacitor voltages, and stable mode transitions under varying load and input conditions. The proposed topology and control strategy offer a practical solution for wide-voltage DC-DC conversion in renewable energy and electric vehicle charging systems, achieving high efficiency and reduced voltage stress without the complexity of clamped or flying-capacitor three-level topologies.