Over-Current Mechanism and Suppression Strategy of DC Transformer in Multiterminal Interconnected Flexible DC Distribution Network

Direct current (dc) transformers are an important component of the multiterminal interconnected flexible dc distribution network. However, it is apt to suffer from the inrush current, which can trigger the shutdown protection and threaten the reliability of the system and equipment. In this article, a 2-MW dc transformer is developed for a T-connected star type multiterminal flexible dc distribution network, where the dual active bridge (DAB) converter is one of the important components. The design of the key parameters is also presented. Based on the steady-state model of the dc transformer, the overcurrent mechanism is elaborated and a suppression strategy of H-bridge temporary blocking and DAB not blocking is proposed, which can automatically clear the fault current. Simulations and practical engineering tests are conducted to verify the effectiveness and practicability of the proposed method, which provides engineering practical value.