Modular multilevel topological structure based on coupling inductor double step-down type submodule and control method thereof

Abstract

The invention discloses a modular multilevel topological structure based on a coupling inductor double step-down type submodule and a control method thereof. Each of upper and lower bridge arms of the topological structure respectively comprises N coupling inductor double step-down type sub-modules capable of outputting three levels, so that output voltage distortion caused by bridge arm direct connection and dead zones of a traditional half-bridge sub-module is avoided, and the output electric energy quality and the power density of the converter are effectively improved. In a single-phase topology, the far ends of the upper bridge arm and the lower bridge arm are used as a common direct current end of a converter; the submodules of the upper bridge arm and the lower bridge arm are connected with a coupling inductor in series, and the midpoint of the coupling inductor is led out and connected with an external alternating current system. In addition, in the control method of the topological structure, the voltage loop is used for adjusting a common-mode voltage, the current loop is used for adjusting the common-mode and differential-mode current, and a current loop for controlling the common-mode current of the sub-module is additionally arranged to obtain a certain direct-current bias, so that the sub-module keeps a current continuous working condition, the dynamic performance of the topological structure is improved, and the safe and reliable operation of the topological structure is ensured.

Description

Technical field [0001] The invention belongs to the technical field of high-voltage and high-power power electronics, and mainly relates to a modular multilevel topological structure based on a coupled inductance double-buck sub-module and a control method thereof. Background technique [0002] Modular multi-level converters have a series of advantages such as common DC interface, strong fault tolerance, output voltage close to sine wave, two-way flow of energy and four-quadrant operation, etc., so they are widely used in high voltage DC transmission systems, static reactive power compensation A series of high-voltage and high-power applications such as a series of high-voltage and high-power applications, such as a series of high-voltage and high-power applications such as a series of high-voltage and high-power applications such as the unified power flow controller, medium and high voltage motor drives and active filters. [0003] However, the traditional modular multilevel conve...

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Problems solved by technology

[0003] However, the traditional modular multilevel converter uses a half-bridge structure as a sub-module, which has the disadvantage of bridge arm direct connection, that is, when the upper and lower switch tubes of the bridge arm are turned on at the same time, the DC side capacitor is short-circuited, causing system failure

In order to overcome the above shortcomings, it is necessary to introduce a dead zone to ensure that the previous switch is completely turned off and then turn on its complementary switch. However, the dead zone also brings narrow pulses, resulting in distortion of the output AC voltage and reducing the power quality. It is especially serious at high switching frequency, so further improvement of modular multilevel topology is needed to suppress the distortion problem caused by dead zone

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