Architecture of Nan'ao multi-terminal VSC-HVDC system and its multi-functional control

This paper presents a framework of a multi-terminal HVDC transmission system and its multi-functional control strategy. The framework possesses the basic characteristics of the DC-grid and is suitable in integrating distributed power sources. The paper proposes the first architecture for a multiterminal HVDC transmission system using the VSC technology. Its control strategy offers various functionalities that include controls for operation mode, start-up and shutdown, DC voltage, and station online re-connecting, which are significantly different from the control of point-to-point VSC-HVDC systems. The framework has not only been evaluated in real-time simulation studies, but has also been implemented onsite for the first time via the China Southern Grid's Nan'ao Multi-terminal VSC-HVDC (VSC-MTDC) project. This paper gives a brief review of the current research and engineering achievements in this field, which includes four aspects: the architecture of the VSC-MTDC system, the structure of the control and protection system, simulation verification tests setting, and the results of real-time hardware in hardware in loop (HIL) simulation studies and onsite tests.