On Features of Direct Current Transformers

Abstract

The open loop operation of the DC transformer requires some intelligence to deal with the system's dynamics and transients. This converter is realized with a bidirectional LLC converter operating close to the resonant frequency and does not receive any voltage or power set points for its operation. This paper presents the required features to enable a safe and autonomous operation. Essentially, DC transformer behaves as an AC transformer, allowing the natural power flow between two dc buses, creating advanced dc grid layouts. Hence, features such as a power reversal algorithm for bidirectional operation, idle mode for the no-load condition, and soft-start and protection are some of the essential features required for its operation. Developed strategies are verified by means of experimental investigations with two similar prototypes evaluating the performance of the strategies and the difference between both DC transformers with the same features.