Two-Stage Parameter Design Methodology of a Generalized Resonant DC Transformer in Hybrid AC/DC Microgrid With Optimum Active Power Transmission

Abstract

A semiregulated high-frequency resonant dc transformer (DCT) is usually recommended to work at its resonant frequency to ensure the desired active power transmission ratio (APTR) with stable voltage conversion gain (VCG) for hybrid ac/dc microgrid. Therefore, appropriately designed resonant parameters are vital in the DCT to acquire the required APTR and VCG under the changing power, temperature, and so on. However, the existing parameter design approach is not general enough to cover different resonant DCT topologies and it becomes rather complex with the increasing number of unknown parameters. To address this concern, a simplified two-stage parameter design methodology is proposed in this article by considering the parameter variation to optimize the APTR on the premise of satisfied VCG. First, a generalized resonant CLLC-type DCT (GCLLC-DCT) is established to cover CLL, LLC, symmetrical CLLC, as well as asymmetrical CLLC topologies. Afterward, based on the design requirements to maximize APTR under stable VCG, the design criteria are presented by analyzing the variation range of the designed intermediated parameters. Subsequently, a two-stage parameter design method is illustrated and facilitated with an example of a DCT prototype based on a simple MATLAB-assisted procedure. Finally, the proposed method is validated by experimental tests.