Flexible DC system starting method and device based on modular multi-level current converter

Abstract

The invention relates to a flexible DC system starting method and device based on a modular multi-level current converter. The device comprises the following steps: S1, after the current converter station uncontrolled charging is finished, newly adding a sub-module for conducting a T2 tube for each bridge arm, thereby gradually adding the number of the submodule of each bypass; charging residual sub-modules to the charging voltage threshold through transformer valve side line voltage, and executing sub-module dynamic voltage-sharing control under a condition of maintaining unchanged total number of the submodule of each bridge arm bypass; S2, when receiving an unlocking instruction, stepping the DC voltage to a rated modulation ratio corresponding numerical value; and S3, after the DC voltage is stabilized, ramping the DC voltage to a DC voltage instruction value, thereby realizing the smooth starting of the flexible DC system. after the uncontrolled charging of the current converter station is finished, the effective voltage-sharing of the current conversion valve submodule at any time slot can be realized, the time for dispatching the unlocking instruction is unlimited, and the AC system impact and heavy harmonic problem caused by low DC voltage at unlocking early stage of the current converter station can be effectively avoided.

Description

technical field [0001] The invention relates to a method and device for starting a flexible direct current system based on a modular multilevel converter, and relates to the field of flexible direct current transmission. Background technique [0002] The flexible DC system based on modular multilevel converters is an important development direction for high-voltage and large-capacity DC transmission due to its small harmonic distortion and low switching loss. The start-up method of the flexible DC system commonly used in engineering can be roughly divided into four steps: 1) The AC incoming circuit breaker of the fixed DC voltage station is closed, and the converter station starts uncontrolled charging through the start-up resistor on the AC side. by figure 1 The modular multilevel converter composed of typical sub-modules shown in the example is taken as an example. When the transformer valve side voltage u ab When >0, the uncontrolled charging circuit of the converter...

AI Technical Summary

Problems solved by technology

[0004] In view of the above problems, the purpose of the present invention is to provide a method and device for starting a flexible DC system based on a modular multi-level converter, which can solve the problem of out-of-control caused by sub-module voltage divergence after uncontrolled charging, and the commutation AC system impact and re-harmonic problems caused by low DC voltage at the initial stage of station unlocking

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