DC line impedance phase protection method based on protection and control cooperation

Abstract

The invention relates to a DC line impedance phase protection method based on protection and control cooperation, the application scene of the protection method is a three-terminal flexible DC power transmission network, and the method calculates the phase angle of input impedance to judge a fault interval by using the high controllability of a converter and injecting a characteristic signal under a characteristic frequency after a fault occurs. And the protection performance is effectively improved. Passive operation is changed into active operation, and non-linear influence of the current converter is avoided. Meanwhile, compared with a full-bridge MMC, the half-bridge MMC does not need to carry out fault ride-through in advance during fault recognition, equipment does not need to be additionally added, fault features can be created, and a fault interval can be reliably recognized; and the protection quickness is improved, and meanwhile better economic benefits are achieved. The method has selectivity, and the whole system cannot be stopped due to the fault of a single line.

Description

technical field [0001] The invention relates to a DC line impedance phase protection method based on protection and control coordination. Background technique [0002] Nowadays, the converters in the flexible DC grid usually use half-bridge sub-modules or full-bridge sub-modules as the basic unit. Due to the large number of sub-modules, the latest level approximation modulation technology is usually used, with active and reactive power decoupling control, power flow Reverse, without filtering and reactive power compensation equipment, and can supply power to islands, etc. In the power system, it provides an effective solution for the concentrated and large-scale development and long-distance transmission of renewable energy, and improves the flexibility and reliability of power grid operation, and is maintaining a trend of rapid development worldwide. However, the damping of the flexible DC system is very small, and the ability of power electronic equipment to withstand ove...

AI Technical Summary

Problems solved by technology

One is to install larger current-limiting reactors on both sides of the line to suppress the rising rate of the fault current, but this solution not only increases the input cost of the power grid, but also affects the dynamic characteristics of the entire power grid

The second is to design a current-limiting strategy after a converter fault. By bypassing a certain number of bridge arm sub-modules, the purpose of suppressing the fault current is achieved. However, while introducing nonlinearity, the original fault characteristics are reduced, which affects the protection. Sensitivity and reliability, which may lead to protection refusal

The third is to use the sub-module reverse input capability of the full-bridge MMC to prevent the sub-module from continuing to feed the fault point. Although the fault current can be greatly limited, the fault transient process is extremely short. In order to protect the available fault transient The state information is extremely scarce, which affects the protection performance

[0005]The existing protection scheme has the following disadvantages: ① In the protection scheme based on traveling wave, it is easily affected by transition resistance and noise interference, and the sensitivity and reliability Affected by control nonlinearity; ②In the scheme based on boundary transient protection, current-limiting reactors need to be configured on both sides of the line at the same time, and at the same time affected by the nonlinearity of converter control; ③Protection scheme based on current differential , is easily affected by the distributed capacitance of the line, and the quick action of the protection is affected; ④The zero-crossing protection based on the full-bridge MMC current limiting control is only suitable for bipolar faults, and the ability to withstand transition resistance is weak; ⑤Based on the full-bridge The realization of the protection scheme of active signal injection of type MMC after the fault rides through, the quick action of the protection is affected

Images