Simultaneous frequency-doubled and frequency-quadruplicated loop current suppression method suitable for MMC (Modular Multi-level Converter)

Abstract

The invention discloses a simultaneous frequency-doubled and frequency-quadruplicated loop current suppression method suitable for an MMC (Modular Multi-level Converter). The method comprises the steps of extracting current values of upper and lower bridge arms of each phase of the MMC, and calculating a loop current value according to the acquired current values; performing frequency-doubled negative sequence and frequency-quadruplicated positive sequence rotating coordinate transformation on the calculated loop current value to transform frequency-doubled and frequency-quadruplicated components into direct-current components respectively; comparing dq axis components of the transformed frequency-doubled and frequency-quadruplicated components of the loop current with a corresponding loop current dq axis component reference value respectively, and then performing linear adjustment control; introducing voltage feed-forward quantities corresponding to the frequency-doubled and frequency-quadruplicated components to eliminate a dq axis coupling part, then obtaining a dq axis reference value for loop current suppression, performing frequency-doubled negative sequence and frequency-quadruplicated positive sequence inverse transformation on the obtained dq axis reference value respectively, adding the obtained corresponding loop current suppression reference values, and adding the sum to a modulated wave signal. The reference value obtained by frequency-doubled negative sequence rotating coordinate transformation on loop current can effectively suppress second harmonic in the loop current.

Description

technical field [0001] The invention relates to a circulating current suppression method suitable for MMC to suppress double frequency and quadruple frequency at the same time. Background technique [0002] Modular Multi-level Converters (MMC) adopts modular design, because of its flexible structure and easy expansion, common DC bus, low switching frequency, low switching loss, improved power quality, four-quadrant operation, etc. The advantage has become one of the most promising topological structures applied to medium and high voltage systems in the new century, and the problem of circulating current suppression is the key to stable and efficient operation of MMC. [0003] In MMC, the main component of the module capacitor voltage is the fundamental component, and the fundamental component can generate a double frequency component in the output voltage, and the double frequency component can also generate a second harmonic in the circulating current. If the second harmon...

AI Technical Summary

Problems solved by technology

If the circulating current is not suppressed, the circulating current will not only increase the rated current capacity of the power switching device, increase the system cost, but also cause serious heating of the power switching device, or even burn it out, affecting the service life of the device

[0004] The double-frequency negative-sequence rotation coordinate change of the existing technology can effectively reduce the double-frequency component in the circulation, but has almost no inhibitory effect on the quadruple-frequency component

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