Rapid protection method and system for DC circuit of multi-port flexible DC power grid

Abstract

The invention discloses a rapid protection method and system for a DC circuit of a multi-port flexible DC power grid. The rapid protection method comprises the following steps of acquiring a voltage and a current of a protection component connected with a positive electrode and a negative electrode of a DC power transmission line; starting a protection device when a short-circuit fault occurs in the power transmission line, and extracting a voltage sampling value and a current sampling value at set time after the fault; calculating FPT according to the voltage sampling value extracted after the fault, and calculating a ratio between a positive current difference value and a negative current difference value at initial time and last time in a sampling data window according to the current sampling value extracted after the fault; comparing the FPT obtained by calculation with a set FPT threshold value, and distinguishing an internal fault and an external fault; and comparing the ratio between the positive current difference value and the negative current difference value which are obtained by calculation with a set threshold value, and distinguishing a fault level. The protection method is rapid in action speed, and the rapidness requirement of the multi-port flexible DC power grid on protection can be met only according to single-end voltage and current of a protected circuit.

Description

technical field [0001] The invention relates to the technical field of DC line fault discrimination of a multi-terminal flexible DC grid in a power system, in particular to a method and system for fast protection of a DC line in a multi-terminal flexible DC grid. Background technique [0002] Compared with the traditional line-commutated converter (LCC) and two-level voltage source converter (VSC), the half-bridge modular multilevel converter (HB-MMC) is gradually applied because of its significant advantages. In the two-terminal flexible DC power transmission project, and will be widely used in many multi-terminal flexible DC power grid projects to be constructed. Compared with the two-terminal DC transmission system, the multi-terminal flexible DC power grid has significant advantages, such as the transmission line has more redundancy to improve the reliability of power supply, the number of required converter stations is reduced, and the construction cost and overall powe...

AI Technical Summary

Problems solved by technology

However, this protection method is seriously affected by the fault resistance. In addition, this protection method does not consider the requirements of the multi-terminal flexible DC grid for the quick action of the protection.

[0007] From the above analysis, it can be seen that the existing DC power grid protection methods based on voltage change rate, traveling wave and parameter identification are seriously affected by fault resistance, and some protection methods cannot meet the protection speed requirements of the DC system.

In addition, most current protection methods can only be applied to symmetrical unipolar DC systems, but few protection methods are suitable for symmetrical bipolar systems

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