Auxiliary capacitance concentrated type half-bridge/single-clamping parallel-serial MMC self-voltage-sharing topology based on inequality constraints

Abstract

The invention provides an auxiliary capacitance concentrated type half-bridge / single-clamping parallel-serial MMC self-voltage-sharing topology based on inequality constraints. In the half-bridge / single-clamping parallel-serial MMC self-voltage-sharing topology, a half-bridge / single-clamping parallel-serial MMC model is electrically connected with a self-voltage-sharing auxiliary loop through 6N auxiliary switches in the auxiliary loop; the auxiliary switches are switched on, and the half-bridge / single-clamping parallel-serial MMC model and the self-voltage-sharing auxiliary loop form the auxiliary capacitance concentrated type half-bridge / single-clamping parallel-serial MMC self-voltage-sharing topology based on the inequality constraints; the auxiliary switches are switched off, and the topology is equivalent to the half-bridge / single-clamping parallel-serial MMC topology. Under the condition of not emphasizing the differences between the two topologies, 6K mechanical switches in the auxiliary switches can be omitted. By means of the half-bridge / single-clamping parallel-serial MMC self-voltage-sharing topology, DC side failures can be clamped without depending on special voltage-sharing control; the capacitances and voltages of sub-modules can be balanced spontaneously on the basis of completing DC and AC energy conversion; in addition, the triggering frequencies and capacitance values of the sub-modules can be correspondingly reduced, and base-frequency modulation of MMC is achieved.

Description

technical field [0001] The invention relates to the field of flexible power transmission, in particular to an auxiliary capacitance centralized half-bridge / single-clamp hybrid MMC self-equalizing topology based on inequality constraints. Background technique [0002] Modular multilevel converter (MMC) is the development direction of DC transmission technology in the future. MMC uses sub-module (SM) cascading to construct converter valves, which avoids the direct series connection of a large number of devices and reduces the impact on devices. Consistency requirements, while easy to expand and redundant configuration. As the number of levels increases, the output waveform is close to sinusoidal, which can effectively avoid the defects of low-level VSC-HVDC. [0003] The half-bridge / single-clamp hybrid MMC is composed of a half-bridge sub-module and a single-clamp sub-module. The half-bridge sub-module consists of 2 IGBT modules, 1 sub-module capacitor, 1 thyristor and 1 mec...

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Problems solved by technology

However, the design of this scheme destroys the modular characteristics of the sub-modules to a certain extent, and the capacitive energy exchange channel of the sub-modules is also limited to the phase, which fails to make full use of the existing structure of the MMC, and the introduction of three transformers complicates the control strategy. At the same time, it will also bring a large transformation cost

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