Multi-level voltage source current converter and control method thereof

Abstract

The invention discloses a multi-level voltage source current converter comprises at least one phase unit. Each phase unit comprises an upper bridge arm, a lower bridge arm and a current conversion electric reactor, wherein the upper bridge arm and the lower bridge arm respectively comprise at least two sub-modules, a switch loop and a bridge arm electric reactor all of which are sequentially connected in series; all sub-modules in the same bridge arm are connected in series in the same direction; the sub-modules, connected with the switch loop, in the upper bridge arm are opposite to the sub-modules, connected with the switch loop, in the lower bridge arm in polarity; one end, connected with the electric reactor in series, of the upper bridge arm and one end, connected with the electric reactor in series, of the lower bridge arm are connected and have access to an alternating current network through the current conversion electric reactor; the other end of the upper bridge arm and the other end of the lower bridge arm serve as a first direct current endpoint and a second direct current endpoint of the phase unit respectively to have access to a direct current network. Each switch loop comprises a plurality of anti-parallel thyristor pairs which are connected in series. The multi-level voltage source current converter is applied to flexible direct-current transmission and the like, and has the advantages of being small in number of the sub-modules, low in cost, small in consumption, capable of effectively blocking fault currents when the direct current side breaks down, and the like. The invention further discloses a control method of the multi-level voltage source current converter.

Description

Technical field [0001] The invention belongs to the field of flexible direct current transmission, and particularly relates to a multi-level voltage source converter and a control method thereof. Background technique [0002] Flexible DC transmission adopts voltage source converters, which can independently adjust the transmission of active and reactive power, improve the transmission capacity of the AC system, and easily form a multi-terminal DC transmission system, which can be used for grid connection of renewable energy generation, power supply in isolated cities, and AC system interconnection And other application fields, has obvious competitiveness. [0003] Currently, flexible DC transmission systems use more topological structures: two-level, three-level topologies and modular multi-level structures. Each bridge arm of the two-level structure of the voltage source converter is directly connected in series by multiple fully-controlled IGBT switches, and the voltage of the p...

AI Technical Summary

Problems solved by technology

[0004] For the voltage source converters of the above three topologies, when the DC side fails, the AC side will feed a large fault current through the diode connected in parallel with the switching device. 40~60ms), the circuit breaker on the AC side is cut off, which seriously threatens the safety of the converter, and therefore requires an additional protection circuit

For multi-terminal DC power grids, the DC power transmission system using these topologies must jump off the AC side switches of all converters to clear the fault when the DC side is faulty, which has a serious impact on the operation of the power grid.

[0005] At present, the voltage source converter mainly uses IGBT as the switching device. IGBT has large loss, low withstand voltage and high cost, which restricts the application and development of voltage source DC transmission to a certain extent.

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