An LLC Resonant Single-Stage Inverter With High-Frequency Link and Soft-Switching

High-frequency-link converters play a significant role in the new generation of smart grids and power systems. Usually, high-frequency-link inverters adopt voltage-fed topologies. However, in dc converters, the widely used LLC topology is a current-fed structure, which has the advantages of soft-switching and high efficiency. The disadvantage of the LLC topology is that the operating range is narrow in the traditional operating mode. With the development of topologies and control strategies, LLC converters are also well employed in wide input or output range occasions. Based on this, this article proposes a single-stage inverter with the LLC topology. The proposed inverter employs a topology-morphing of full-bridge (FB) to half-bridge (HB) and a hybrid control strategy of the pulse frequency modulation (PFM) combined with the pulsewidth modulation (PWM). The operating area is divided into three regions according to the output voltage. The FB-PFM, HB-PFM, and HB-PWM are adopted in different regions, so as to achieve a narrow frequency range and full soft-switching. Operation principles and characteristics of the proposed inverter are analyzed in detail, and the key parameters of the inverter are designed. To verify the proposed scheme, a 2 kW prototype of 480 V input and 220 V/50 Hz output was built and tested with a maximum efficiency of 97.6%.