Resonant Point Analysis of Generalized CLLC-Type DC Transformer in the Hybrid AC/DC Microgrid

The CLLC-type resonant DC Transformer (simplified as DCT) has been proposed in the coexisting hybrid AC/DC microgrid to substitute the traditional bulky line-frequency AC transformer. It can ensure the bus voltage matching and galvanic isolation as the high-frequency operating condition, high power-density as well as the adjustable characteristics. However, it is worthy pointing out that the hybrid AC/DC microgrid is a special application, which often poses a series of specific challenges to the DCT design, such as the transmission power features, efficiency, etc., which largely depend on the deviation between the switching and resonant frequency. Therefore, the resonant point of the CLLC-type resonant DCT is analyzed to guide its future parameters design in the hybrid AC/DC microgrid. Based on the system description, the equivalent mathematic model of the CLLC-type DCT is established to derive the resonant point number under various load conditions by minimizing the reactive power. An example is given with the simulation results to verify the theoretical analysis. Lab-scale CLLC-type DCT prototype has been developed for experimental verifications.