Commutation failure suppression method for non-faulty strata converters in stratified access uhvdc system

Abstract

The invention discloses a commutation failure suppression method for layered access to non-faulty layer converters of a UHVDC system. AC system voltage disturbance; if the collected analog quantity exceeds the set value, the constant turn-off area control is performed; 2. The AC side fault layer and the non-fault layer are discriminated, and the DC current of the non-fault layer converter is increased 3. After the fault is cleared, restore the cut-off angle to the rated value, and release the output limit of the trigger lead angle. The invention can effectively suppress the commutation failure of the non-faulty layer converters of the layered access UHVDC system, thereby improving the transient response characteristics of the system during the fault period, reducing the power fluctuation caused by the commutation failure of the inverter station, and reducing the impact on the AC Grid shock.

Description

technical field [0001] The invention relates to a method for suppressing the commutation failure of a non-faulty layer converter of a layered access UHVDC system, and belongs to the technical field of high-voltage direct current transmission. Background technique [0002] With the increasing demand for large-capacity and long-distance power transmission, HVDC transmission based on grid commutation converters has been widely used in DC power transmission projects due to its outstanding economical and long-distance power transmission advantages. The inverter based on grid commutation uses thyristor without self-shutdown capability as the commutation element. When the voltage of the receiving end grid is disturbed, the commutation failure is very likely to occur, which is easy to cause large fluctuations in power transmission and seriously threaten the security of the grid. In recent years, the transmission power of UHV DC transmission has been increasing continuously. In order...

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Problems solved by technology

[0003] 1) There is electrical coupling between the two AC power grids connected to the receiving end. When the voltage of one of the power grids is disturbed, the voltage of the other power grid will drop or be distorted, thereby affecting the normal operation of the converter. Low-end converters will fail commutation due to fluctuations in commutation voltage;

[0004] 2) The DC sides of the high-end and low-end converters are connected in series so that the DC currents of the two converters are the same. When a commutation failure occurs in one converter, the DC current will increase rapidly, thereby affecting the normal commutation of the other converter , causing the commutation failure of the high-end and low-end converters at the same time

However, in the currently published patents, the coordinated control of the high-end and low-end converters proposed in the layered access mode seldom comprehensively considers the AC voltage and DC current of the grid that cause commutation failure, which affects the judgment of commutation failure Accuracy, the control strategy to suppress commutation failure needs to be further improved

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