Multitime Scale Frequency Regulation of a General Resonant DC Transformer in a Hybrid AC/DC Microgrid

Abstract

The high-frequency resonant dc transformer (DCT) becomes popular in hybrid ac/dc microgrids, thanks to its good bidirectional power transmission (PT) ability and high power density. However, its application is limited by either the complex systematic control or the complicated parameter design. To solve this problem, in this article, a multitime scale frequency regulation approach is put forward for a general CLLC-DCT (GCLLC-DCT). By establishing the general model of the resonant DCT, the relationship between the transmitted power and the resonant frequency is derived at first. Afterward, the power trigger mechanism is introduced to assist the implementation of the proposed approach. If the long-time scale control is triggered, only once calculation based on the PT requirement will be introduced to avoid redundant computations. If the short-time scale control is triggered, the frequency regulation based on the voltage conversion gain feature of GCLLC-DCT will be executed till it reaches a new steady state, which is beneficial to ensure the real-time control precision. The cooperation of the short-time and long-time scale control is also presented to make the proposed approach easily implement at hybrid ac/dc microgrids. The lab-scale prototype of GCLLC-DCT has been set up based on a hybrid ac/dc microgrid to verify the superiority of the proposed approach.