MMC suppression common mode voltage modulation method and system suitable for even number of sub-modules

Abstract

The invention discloses a modulation method and a system for suppressing a common-mode voltage by an MMC suitable for an even number of sub-modules, and belongs to the field of electric power. Including: converting the three-phase reference voltage analog linear operation into three reference line voltage analogs injected into the zero-sequence component; for MMC with 2N sub-modules, combining the three reference line voltage analogs with N carrier waves stacked in phase Carrier comparison is performed separately to obtain three driving signal digital quantities; the three driving signal digital quantities are linearly transformed into three-phase reference voltage digital quantities of MMC; the three-phase reference voltage digital quantities of MMC are distributed to sub-modules to control MMC, Get the drive signals of all the switch tubes in the MMC. The present invention equivalently realizes the transmission of zero common-mode voltage vector through the addition and subtraction of carrier comparison, greatly reduces the common-mode voltage, suppresses the common-mode current coupled by stray capacitive coupling, and is simple to implement, avoiding the reference of the traditional method based on space vector synthesis Complicated calculations such as vector positioning.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and more particularly relates to a modulation method and system for suppressing a common-mode voltage by an MMC suitable for an even number of sub-modules. Background technique [0002] Modular multilevel converter (MMC) is considered to be the most potential interface for medium and high voltage power conversion sites due to its excellent performance. In addition to being used as a converter valve in high-voltage direct current transmission, it also has application prospects in some occasions where the voltage level is relatively low, such as motor control systems and photovoltaic power generation systems. At this time, the number of sub-modules of the MMC is relatively small, so a modulation method with a high switching frequency such as carrier stacking or carrier shifting is used to control the MMC. [0003] Conventional carrier stacking or phase-shifting methods will generate comm...

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Problems solved by technology

[0004] Aiming at the defects and improvement needs that the motor bearings of the motor system using MMC for electric energy conversion in the prior art and the photovoltaic panels of the photovoltaic power generation system are easily damaged by common-mode voltage, the present invention provides an MMC suitable for an even number of sub-modules to suppress the common-mode voltage Modulation method and system, the purpose of which is to reduce the common-mode current and common-mode interference caused by the high-frequency common-mode voltage output by MMC in the traditional modulation mode

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