Capacitance lowering circuits and modularized multi-level current converter

Abstract

The invention provides capacitance lowering circuits and a modularized multi-level current converter comprising the capacitance lowering circuits. Each capacitance lowering circuit comprises a bridgearm reactor L1, a bridge arm reactor L2 and a switching circuit, each switching circuit comprises a first branch circuit and a second branch circuit which are in reverse parallel connection, the firstbranch circuits and the second branch circuits all comprise multiple thyristors in series connection, each bridge arm of the modularized multi-level current converter comprises the corresponding capacitance lowering circuit and multiple submodules, and after being in series connection, the submodules are in series connection with the capacitance lowering circuits. On the premise of meeting fluctuation amplitude design requirements of capacitor voltages of the submodules, capacitance values of capacitors of the submodules are lowered, the adjusting range is large, the capacitance lowering effect is obvious, by allocating reactance values of the upper bridge arm and the lower bridge arm, original energy distribution of the bridge arms is changed, then the capacitor voltage waveform of eachsubsidiary module in the energy transmitting process is changed, the oscillation amplitude of the capacitor voltages of the submodules when the same active power is transmitted is effectively lowered,and thus the capacitor capacitance values of the submodules in the modularized multi-level current converter are lowered.

Description

technical field [0001] The invention relates to the technical field of direct current transmission, in particular to a capacity reduction circuit and a modular multilevel converter including the capacity reduction circuit. Background technique [0002] The flexible DC transmission technology mainly adopts the voltage source converter. The power electronic devices in this type of converter have the advantages of low inertia, four-quadrant operation, and flexible power flow control. The most commonly used structure of the voltage source converter in the flexible DC transmission technology is the modular multilevel converter. The advantages of the modular multilevel converter include: 1) The modular structure makes the system easy to expand, so as to realize Higher voltage level, easy to build redundant structure also improves the reliability of the system; 2) Low switching frequency, reducing switching loss; 3) Can generate more levels, high waveform quality, no need to instal...

AI Technical Summary

Problems solved by technology

[0004] In order to overcome the shortcomings of small adjustment range, poor effect and low accuracy in the above-mentioned prior art, the present invention provides a derating circuit and a modular multilevel converter including the derating circuit. The derating circuit includes the bridge arm reactance L1 , bridge arm reactance L2 and switching circuit, bridge arm reactance L1 and bridge arm reactance L2 are connected in series, switching circuit and bridge arm reactance L1 are connected in parallel, switching circuit includes anti-parallel first branch and second branch, the first Both the branch and the second branch include multiple thyristors in series, which reduces the capacitance of the sub-module capacitor on the premise of meeting the design requirements of the fluctuation amplitude of the capacitor voltage of the sub-module, with a large adjustment range and a significant derating effect

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