Control method for flexible grid commutation converter to suppress high-voltage DC commutation failure

Abstract

The invention discloses a control method and system for a flexible power grid commutation converter to suppress high-voltage direct current commutation failure, comprising the following steps: cascading an H-bridge in series at the valve side of the converter transformer on the inverter side of the high-voltage direct current transmission A controllable voltage source, the controllable voltage source and the grid commutation converter form a flexible LCC; the controllable voltage source adopts a continuous control method to output capacitive voltage. In the present invention, the flexible LCC can realize the separate control of the DC bus voltage and the actual arc extinguishing angle in the normal operation state; when the voltage drop of different degrees occurs in the AC power grid, the controllable voltage source can effectively suppress the commutation of the grid commutation converter The failure problem occurs.

Description

technical field [0001] The invention belongs to the technical field of suppressing commutation failure of high-voltage direct current, and in particular relates to a control method and system for suppressing commutation failure of high-voltage direct current by adopting a flexible grid commutation converter. Background technique [0002] Conventional DC transmission based on grid-commutated converters will still be the main means of long-distance large-capacity power transmission and asynchronous grid interconnection for a long period of time in the future. Commutation failure is an inherent problem in conventional DC transmission, which occurs in both point-to-point and multi-drop grid systems, and with the increase of system capacity and the number of drop points, the scope of influence of commutation failure will increase. The failure of commutation may lead to the decrease of DC voltage, the reduction of DC transmission power, the increase of current, the shortening of t...

AI Technical Summary

Problems solved by technology

The first type is to install a reactive power compensation device on the inverter side. This method cannot eliminate the commutation failures of the first few times after the fault occurs and the economy is poor.

The second category is to improve the control strategy of the converter, such as advancing the trigger angle of the inverter after the voltage drop is detected. This method may increase the reactive power demand of the converter and further aggravate the voltage drop.

The third category is to set up additional auxiliary commutation devices, such as connecting capacitors in series on the valve side of the converter transformer or using power electronic devices to switch capacitors during the commutation process. Among them, the former may have voltage imbalance when an asymmetrical fault occurs. The latter has relatively high control complexity

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