Multi-input multi-output frequency domain impedance modeling method for modular multilevel converter

Abstract

The invention discloses a multi-input multi-output frequency domain impedance modeling method for a modular multilevel converter. The multi-input multi-output frequency domain impedance modeling method comprises the following steps: establishing a time domain nonlinear three-phase model of the modular multilevel converter; linearizing the time domain nonlinear three-phase model to obtain a time domain linear three-phase model; calculating each harmonic value corresponding to the steady-state working point in the time domain in the frequency domain; performing harmonic expansion on the linear three-phase model in the frequency domain based on the harmonic state space to obtain a linear three-phase harmonic state space model; expanding symmetric transformation in the harmonic space, and converting the linear three-phase harmonic state space model into a positive and negative sequence harmonic state space model; determining strong coupling frequency, and extracting positive and negative sequence components of voltage and current at the alternating current port from the positive and negative sequence harmonic state space model; and based on the positive and negative sequence componentscorresponding to the outlet voltage and current, linearly solving to obtain a multi-input multi-output frequency domain impedance model. According to the invention, internal harmonic coupling and positive and negative sequence coupling are considered, and the multi-input multi-output frequency domain impedance modeling method is more accurate.

Description

Technical field [0001] The present invention relates to the technical field of modular multilevel converters, in particular to a method for modeling multi-input multi-output frequency domain impedance of modular multilevel converters. Background technique [0002] With the rapid development of large-scale wind farms, the demand for modular multi-level converter high voltage direct current transmission (MMC-HVDC) solutions has increased significantly in recent years. Compared with the traditional DC transmission based on two-level voltage source converter (VSC-HVDC), MMC-HVDC has many advantages, such as modularity, high efficiency and lower loss. However, the unique multi-frequency response characteristics of the modular multi-level converter will cause it to produce multiple harmonic coupling in a wide frequency range, which can easily lead to unstable phenomena between the wind farm and MMC-HVDC. Oscillation etc. Therefore, it is very important to establish an accurate modula...

AI Technical Summary

Problems solved by technology

In the past research, most researchers simplified the three-phase model of the modular multilevel converter into a single-phase model in order to simplify the model, which is not enough to consider all the coupling between phase sequences

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