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

Abstract

The invention discloses a modulation method and system suitable for MMC suppression common-mode voltage of an even number of sub-modules, which belongs to the field of electric power. The method comprises the following steps of converting three-phase reference voltage analog quantity linear operation into three reference line voltage analog quantities injected with zero-sequence components, for the MMC with 2N sub-modules, respectively carrying out carrier comparison on the three reference line voltage analog quantities and N in-phase stacked carriers to obtain three driving signal digital quantities, linearly converting the three driving signal digital quantities into a three-phase reference voltage digital quantity of the MMC, and distributing the three-phase reference voltage digital quantity of the MMC to the sub-modules to control the MMC so as to obtain driving signals of all switching tubes in the MMC. According to the method, the zero common-mode voltage vector is equivalentlytransmitted in a carrier comparison addition and subtraction mode, the common-mode voltage is greatly reduced, the stray capacitance coupled common-mode current is suppressed, the method is easy to implement, and complicated calculation such as reference vector positioning based on a traditional space vector synthesis method is avoided.

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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