AC/DC decoupling control method of modular multi-level current converter and application thereof

Abstract

The invention discloses an AC / DC decoupling control method of a modular multi-level current converter. The method comprises the steps of adding DC current control in current inner-loop control so that current inner-loop control comprises AC current control and DC current control, thereby using output of the AC current control and output of the DC current control as main components of an output voltage reference value of each phase leg of the modular multi-level current converter; respectively controlling reference values of the AC current control and the DC current control, and simultaneously controlling outputs of the AC current control and the DC current control, thereby realizing control on main components, and furthermore preventing current converter locking because of a leg overcurrent in DC fault. The invention further discloses application of the method in a flexible DC power transmission system. The AC current and the DC current of each current converter station and capacitance and voltage of each submodule are controlled into a safe range, thereby realizing DC fault crossing of the flexible DC power transmission system.

Description

technical field [0001] The invention belongs to the technical field of electric power transmission and distribution, and more specifically relates to an AC / DC decoupling control method for a modular multilevel converter and its application in an overhead DC transmission system. Background technique [0002] Modular Multilevel Converter (MMC) technology has the advantages of modular structure and easy expansion. Since it was proposed, it has been widely used in the industry. So far, all the MMC HVDC transmission projects in the world have adopted the half-bridge type MMC technology based on the half-bridge sub-module (HBSM) or the same type of half-bridge sub-module (HBSM). Flat (Cascaded two level, CTL) technology. However, both the half-bridge MMC and CTL have the problem of being unable to cope with DC faults. After a DC fault occurs on the transmission line, the AC system will continue to provide fault current to the fault point through the freewheeling diode of the hal...

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Problems solved by technology

The scheme of Kong Ming et al. has similarities with the scheme of CN104300569, the difference is that the residual voltage value of the DC side is not monitored in real time, but the residual voltage value of the DC side is artificially set to zero. The module capacitor voltage forms a closed-loop control, so there is a potential safety hazard of overcurrent or submodule capacitor overvoltage. Figure 12 It can be seen that during the DC fault, the DC current value rises from 1.6kA in the steady state to about 8kA at the moment of the fault, and the DC overcurrent multiple is as high as 5 times, which may burn the MMC

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