MMC-HVDC direct-current short-circuit fault ride-through method based on direct-current bus bipolar equipotential

Abstract

The invention relates to an MMC-HVDC direct-current short-circuit fault ride-through method based on the direct-current bus bipolar equipotential, and belongs to a direct-current fault protection method of a flexible direct-current power transmission system. According to the method, the double-pole potential of the MMC direct-current side bus is controlled to be approximately equal, so that the short-circuit fault current of the direct-current side is close to zero, and the direct-current bipolar short-circuit fault ride-through can be realized under the condition that the MMC is controllable. The basic principle is that after the direct-current short-circuit current is detected, a fault operation mode is adopted, and on and off states of upper and lower three-phase bridge arms of the MMC three-phase are selected according to the polarity of the power grid voltage, the MMC circuit topology is equivalent to the chain type star topology, and the three-phase conducted upper and lower bridge arm voltage is controlled to withstand the voltage of the power grid, and the double-pole electric potential of the direct-current bus is approximately equal, the direct-current side short-circuit fault current is close to zero. An alternating-current circuit breaker is not needed, and the capacitor voltage balance of the MMC sub-module is maintained during the fault ride-through period, and after the fault is eliminated, the power transmission can be rapidly restored.

Description

technical field [0001] The invention relates to an MMC-HVDC DC short-circuit fault ride-through method based on bipolar equipotentiality of a DC bus, which belongs to a DC fault control and protection method for a flexible DC transmission system. Background technique [0002] The MMC-based flexible DC transmission technology has the advantages of being economical and flexible, can supply power to passive networks, independently control active power and reactive power, and output high-quality power. Distance from large-capacity power transmission and other fields. Although flexible DC transmission has many advantages mentioned above, in the current flexible DC transmission projects, whether it is two-level, three-level or half-bridge MMC topology, it cannot pass through the blocking converter when the DC side line fails. Quickly interrupt fault current. And because the DC fault current cannot naturally cross the zero point, it is difficult to extinguish the arc, and the com...

AI Technical Summary

Problems solved by technology

This method can only be applied to the full-bridge sub-module structure, which uses twice as many IGBTs as the half-bridge sub-module

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