利用单端电气量的VSC-HVDC输电线路保护新原理

VSC-HVDC (voltage source converter HVDC) control system is very complex and has poor fault tolerance ability. So researches on high-performance protection which is suitable for VSC-HVDC system is necessary. Because of the special structure of VSC-HVDC system, namely the existence of a large capacitor on both sides of the line, the capacitors store a lot of energy during normal operation. When a fault occurs outside the lines, voltage decreases in fault position and the capacitor discharges outside. The discharge current is much larger than the DC line's injection current. The current which flows into the opposite inverter and the capacitor's discharge current have the same direction; when the fault occurs inside the line, there are high-frequency signals in the capacitor discharge current. It makes the current which flows into the opposite inverter change direction. With this feature, this paper proposed a new protection principle for VSC-HVDC transmission lines based on single-end electrical quantity. Using the proposed protective principle, whether the fault is inside or outside the protection zone can be effectively recognized and there is no strict requirement on sampling frequency. A large number of simulation results show that the proposed protection can reliably distinguish between inside fault and outside fault.