Fault Control of AC-DC Hybrid Distribution Network Based on Active Injection of High-Frequency Signal

AC/DC hybrid distribution network is an important development direction of future distribution system, and DC interpole short circuit fault is the most serious fault type in DC distribution network. Usually, the blocking converter is used to isolate the fault current. Under this protection, the effective value of fault information is less, and the fault location is difficult to be identified by the protection device. To solve this problem, a new fault control strategy is proposed. By switching the control strategy of PET (Power Electronic Transformer), the input stage adopts current limiting control and changes the switching frequency of the output stage. A high frequency signal is injected into the fault point to make the protection device quickly identify the fault. Firstly, the short-circuit fault characteristics of DC distribution network are analyzed. Secondly, the generation mechanism and selection principle of characteristic signal are given from the perspective of feasibility. Then, the control strategy of injecting characteristic signal into fault lines is discussed. Finally, the feasibility and effectiveness of the proposed method are verified by simulation.