The quaterly meeting of Project IV (‘Research on protection methods and key technology of multi-voltage DC distribution systems’), National Key Research and Development Project (‘Key technology and application of mid and low DC distribution systems”) was hold in Southeast University. Dr. Yu Liu was invited to attend the meeting by Dr. Zaijun Wu, Department of Electrical Power Engineering, Southeast University. Other participants of this meeting include top researchers from Southeast University, Tianjin University, Harbin Institute of Technology, NARI Electric and State Grid JiangSu Electric Power Company Research Institute.