Surge Current Reduction in LLC Resonant Converter with PSM under Light Load Condition

This study assumes the utilization of the LLC resonant converter as an on-board charger, employing both pulse frequency modulation (PFM) and phase shift modulation (PSM) together to extend the output voltage range. However, it has been observed that when operating the PSM under light load conditions, a surge current emerges in the output current. Through some analysis, it has been determined that the surge current is caused by the deterioration of the main circuit characteristics due to the junction capacitance of the secondary diode. Therefore, secondary short-circuit control using a secondary-side active switch with PWM is proposed for surge current reduction. The article presents an explanation of the issue and introduces the suggested secondary short-circuit control strategy. Experimental findings demonstrate that the proposed control strategy effectively reduces the surge current.