Protection Scheme for Flexible HVDC Transmission Line Based on Virtual Impedance Voltage Characteristic

The traditional flexible HVDC system protection scheme based on boundary conditions uses current-limiting reactors to extract fault features. When the size of the reactor is limited by the actual engineering, there is a problem that the protection is difficult to identify the fault. This paper takes the flexible HVDC transmission line as the research object. Considering the limited value of the current limiting reactor, a virtual impedance link is added to the control system to limit the fault current. Combined with the transient voltages of virtual impedance and current limiting reactor, a protection scheme is jointly constructed to identify the fault. The fault feature quantity composed of the traditional protection electrical quantity and the control quantity can improve the sensitivity and reliability of the protection, and effectively carry out fault identification.