A pulse width modulated LLC type resonant topology adpated to wide output voltage range

In a two stage LLC based plug-in electric vehicle (PEV) onboard charger, the dc link voltage is usually kept constant while the battery pack voltage varies in a wide range. This makes it extremely difficult to optimally design the second stage pulse frequency modulated (PFM) LLC resonant converter. In this paper, a modified pulse width modulated (PWM) LLC resonant topology is proposed and investigated in PEV charging applications. The proposed converter is able to achieve wide output voltage range, while maintaining the switching frequency of the full bridge constant and equal to the resonant frequency. In comparison with the conventional LLC topology, only one auxiliary MOSFET is added. Zero-voltage-switching (ZVS) is realized among all power MOSFETs. A 1.2 kW converter prototype, generating 250V-420V output voltages from the 390 V dc link, is analyzed, designed, and simulated to verify the proof of concept.