Abstract
The LLC resonant converter operated with fixed switching frequency can realize the function of dc transformer (DCX) and achieve high efficiency. To regulate the output voltage, a preregulator or postregulator is required, and thus constituting the DCX-LLC resonant converter based two-stage dc-dc converters, including the preregulator+LLC and LLC+postregulator converters. In this paper, it is found that there are two resonant peaks in the voltage-loop gain of the preregulator+LLC converter, which limits the crossover frequency and degrades the dynamic performance. To suppress the resonant peak, the virtual resistor introduced into output rectifier scheme (VR-ORS) for damping the resonant peak and the notch filter with specific gain inserted into voltage loop scheme (NF-VLS) for eliminating the resonant peak, are proposed, respectively. The implementation of the two approaches is derived and the design considerations of the voltage-loop compensator are presented. Finally, a 6-kW preregulator+ LLC converter is fabricated and tested in the lab. The experimental results are provided to verify the effectiveness of the proposed resonant peak suppression approaches for improving the dynamic performance.
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