Method of controlling running of modularized multi-level converter in low frequency model

Abstract

The invention relates to a method of controlling running of a modularized multi-level converter in a low frequency model, which belongs to the technical field of controlling multi-level power electronic converters. The method comprises the following steps: setting high frequency common mode voltage and high frequency ring current both required to be superimposed, revising a switching function of a submodule and bridge arm current, obtaining an expression of capacitance voltage differential coefficient of the submodule according to volt-ampere characteristics of capacitance of the submodule, and in order to allow the capacitance voltage of the submodule to only have high-frequency component, assuming high frequency common mode voltage is known to obtain a expression of the high frequency circular current; comparing a running frequency with a critical frequency to obtain frequency model selection signals, combining an energy control and a circular current control of a phase unit of the modularized multi-level converter, determining whether the high frequency common mode voltage and the high frequency circular current are required to be superimposed to an original instruction or not according to the frequency model selection signals, and generating voltage required to be superimposed in the bridge arm of the phase unit of the high frequency circular current by controlling. The method is easy to realize and strong in universality, and provides reference for low frequency application of the modularized multi-level converter.

Description

technical field [0001] The invention relates to a control method of a modular multilevel converter, in particular to an operation control method of a modular multilevel converter in a low-frequency mode, and belongs to the technical field of control of multilevel power electronic converters. Background technique [0002] The modular multilevel converter is a multilevel power electronic converter topology proposed in 2001. It realizes high voltage and multilevel output through the cascading of sub-modules, and has very good scalability. The modular multilevel converters are connected back to back to form a common DC bus, which is suitable for the field of "AC-DC-AC" power conversion, such as high-voltage frequency conversion speed regulation and electric locomotive traction. When a modular multilevel converter is used as a variable frequency speed control drive for a high-voltage motor, the motor side converter usually uses a modular multilevel converter with three phase unit...

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Problems solved by technology

[0004] The purpose of the present invention is to propose an easy-to-implement low-frequency mode operation control method of a modular multilevel converter, in which a certain high-frequency common-mode voltage is superimposed in the output voltage command of the modular multilevel converter, and the bridge arm A certain high-frequency circulating current is superimposed in the circulating current command. By controlling the output voltage and the bridge arm circulating current to follow the command value, the fluctuation frequency of the sub-module capacitor voltage is increased to solve the problem of sub-module capacitance when the modular multilevel converter operates in low-frequency mode. The problem of excessive voltage fluctuation is suitable for modular multilevel converters with 3 phase units and 2 phase units

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