Optimal Design Considerations for a Modified LLC converter with wide input voltage range capability suitable for PV applications

The paper proposed a modified LLC converter with two transformers in series, which has four operation configurations, covering the range of four times the minimum input voltage. To optimize the proposed LLC converter in attempt to achieve good efficiency, a numerical method is developed based on the LLC converter's steady state equations. Optimal criterion and optimization procedure are given to guide optimal design for LLC converters and an optimal design example is given as well. A 250W 210V output prototype with input voltage ranging from 25V to 100V is built to verify the proposed converter and the developed numerical model. Experimental results show the proposed converter can achieve the efficiency up to 98%, while maintaining a very wide input voltage range.