Resonant Peak Suppression Approaches for Improving the Dynamic Performance of DCX-LLC Resonant Converter Based Two-Stage DC-DC Converter

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 article, 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 for damping the resonant peak and the notch filter with specific gain inserted into voltage loop scheme 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.