Study On DC Micro-grid For Distributed Power Access

The existing distribution network has convenient voltage changing and mature protective relaying technologies but faces the problems such as insufficient power supply, transmission corridors constraint, poor power quality and access of the distributed power (including electric vehicle charging stations). With the advantages of light-HVDC technology, the DC micro-grid is a good way to solve the problems in existing distribution network and meet the needs of future distribution network.This paper study on DC micro-grid for distributed power access, including:the topology and voltage level of DC micro-grid, the characteristics and access methods of distributed power, and the interface technology between DC micro-grid and AC distribution network. In addition, this paper proposed a new power electronics device named SSSC-FCL. Take the advantage of this device the regulation of power flow on AC system and limit the AC short circuit current can be achieved. On this basis, the three-layer control method for DC micro-grid is put forward. The proposed control method can follow the power characteristics of the distributed power to achieve efficient use of solar energy and other new energy. Others, it can also ensure the power flow regulation on AC transmission lines; Under short-circuit faults, it can quickly limit the AC short circuit current, isolate the fault zone, ensure normal supply of non-fault region, provide emergency power supply. In the end, the feasibility and reliability of the proposed system and control method are verified by results of PSCAD/EMTDC-based simulation.