General loop current control method for modular multi-level converter considering low frequency oscillation

Abstract

The invention discloses a general loop current control method for a modular multi-level converter considering low frequency oscillation. The general loop current control method is mainly used for restraining a low frequency oscillation loop current and a second harmonic generation loop current in a bridge arm loop current of the modular multi-level converter. The relation between a bridge arm voltage and the bridge arm loop current is analyzed to obtain the oscillation frequency of the low frequency oscillation loop current of the converter so as to provide beneficial evidence for the design of a control system; the cut-off frequency of a low pass filter is set according to the calculated value of the oscillation frequency; the bridge arm loop current passes through the low pass filter to obtain a direct current component, and then the direct current component is subtracted by the bridge arm loop current to obtain an alternating component of the bridge arm loop current; the alternating component contains a harmonic component of the low frequency oscillation loop current and a harmonic component of the second harmonic generation loop current; the alternating component passes through a regulator to obtain a control reference voltage of the bridge arm loop current, and the control reference voltage is added to a modulating signal. By means of the general loop current control method, a low frequency oscillation component and a second harmonic generation component in the bridge arm loop current are simultaneously restrained, the loop current control system is simplified, split-phase control over the loop currents is realized, loss of the converter is lowered, and the dynamic stability of the system is enhanced.

Description

technical field [0001] The invention relates to a control method in the field of light direct current transmission (VSC-HVDC), in particular to a general circulation control method for a modular multilevel converter considering low-frequency oscillation. Background technique [0002] The superior performance of direct current transmission in long-distance power transmission makes it have extremely promising application prospects in long-distance transmission of renewable energy such as wind power and offshore power generation. The modular multilevel converter is based on the medium voltage of light direct current transmission Novel topology of source converter (VSC-HVDC). Modular multilevel converters have been widely researched and applied in the fields of light DC transmission and medium and high voltage reactive power compensation due to their advantages of high power factor, low distortion rate, small device withstand voltage, and good fault tolerance redundancy. Altern...

AI Technical Summary

Problems solved by technology

In the operation of the converter, because the actual working conditions are much more complicated than the ideal conditions, the bridge arm current is distorted, and its components also contain double frequency and its multiple sub-harmonic currents, as well as possible low-frequency oscillating currents, which not only increase the sub- The current stress of the module and the reactance also increases the loss of the converter, and the system will not operate normally in severe cases

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