Pole-to-Ground Fault Protection Scheme for Flexible DC Distribution Network Based on Time Domain Skewness and Integral Energy

For the multi terminal flexible DC distribution network based on modular multilevel converters, if the line fails and is not cut off in time, it will damage power electronic devices and may burn out the converter station. It is difficult to accurately distinguish between internal high resistance faults and external low resistance faults when faults occur in multi terminal flexible DC distribution networks. Analyzed the equivalent model and equation of zero-mode current at each measurement point in the time domain and complex frequency domain when a grounding fault occurs in the system. Based on this, a flexible DC distribution network grounding protection method based on time domain skewness and integral energy is proposed. Using the zero-mode current skewness symbol at each measuring point to characterize directional characteristics, and the integrated energy of the line to characterize amplitude characteristics. Using integrated energy as a supplement to skewness criteria can accurately extract fault features and perform fault identification in extreme cases where a certain line is long. Finally, a four-terminal flexible DC power grid model was built on the PSCAD/EMTDC simulation platform to verify the adaptability and superiority of the protection method.