Pre-charging control method of modular multi-level converter (MMC) and control apparatus thereof

Abstract

The invention provides a pre-charging control method of a modular multi-level converter (MMC) and a control apparatus thereof. The method includes: performing uncontrollable charging on the modular multi-level converter (MMC), and charging a sub-module capacitance series voltage of a charging loop to a charging voltage provided by an alternating current system; determining an upper bridge arm current and a lower bridge arm current of each phase unit and a capacitance voltage of each sub-module; determining the direction of the bridge arm current of the sub-module, and determining whether the bridge arm current is greater than 0; removing the sub-module if the capacitance voltage uci of the sub-module reaches a reference voltage of a stable-state operation voltage, and unlocking the next sub-module for the above operation; repeating the above operation on the sub-modules one by one until the charging of the last sub-module of a bridge arm is accomplished, and returning a marking signal for indicating the completion of charging of the bridge arm; and charging capacitors of the sub-modules of all the bridge arms to the stable-state operation voltage in sequence to accomplish the start process. The method is simple, the extension to different level numbers is facilitated, the capacitance voltage of all the sub-modules can be rapidly increased to the voltage required by stable-state operation of the converter based on uncontrollable charging.

Description

technical field [0001] The invention relates to the technical field of power system flexible direct current transmission and distribution and power electronics, in particular to a modularized multilevel converter MMC precharge control method and a control device thereof. Background technique [0002] Since its inception, modular multilevel converters have received extensive attention from researchers at home and abroad due to their advantages such as flexible control and easy expansion of sub-module structures. Its steady-state operation requires the system to have a certain initial voltage, but MMC is different from the traditional two-level converter, because it contains a large number of suspended sub-module capacitors, at the initial moment, all sub-module capacitors have no initial voltage; Before the state, it is necessary to adopt a corresponding control strategy to charge the sub-module capacitor first, and charge the sub-module capacitor to the steady-state operatin...

AI Technical Summary

Problems solved by technology

The control of the controllable pre-charging process in the above documents is carried out on the premise of bypassing the charging current-limiting resistor. The bypass current limiting resistor in the pre-charge stage limits its current limiting capability

[0009] At present, the existing modular multilevel converter precharge control strategy may have high economic costs, or the current limiting resistor needs to be bypassed during the controllable precharge stage

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