Research on fault current limitation and active control for power electronic transformer in direct current grid

Due to the low impedance of DC (Direct Current) power transmission line, short-circuit current has a very high increment speed, which causes problems as difficulty in current limitation method. This paper proposes a new method to realize the current-limiting control of short-circuit current by using active control of power electronic transformer. The method improves the topology of dual active bridge modules that contribute the DC transformer, and installs an IGBT (Insulated Gate Bipolar Transistor) switch in reverse direction on supporting capacitor branch of each module to control the capacitor on or off, which can guarantee the storage energy within the capacitor will not release in initial stage in case of DC short circuit fault happen. Therefore, there is no large inrush current flow out. Furthermore, combined with the requirements of current tracking control during low-voltage ride-through, the transformer output current under short-circuit condition is actively controlled in order to meet the needs of renewable energy power generation equipment. Finally, the simulation and hardware-in-the-loop experiments verify the correctness of this method.