Novel three-phase serial modular multilevel converter HVDC converter

Abstract

The invention discloses a novel three-phase serial modular multilevel converter HVDC converter, comprising a DC output end, a three-phase AC input end, a first transformer, a second transformer, a third transformer, a first single-phase converter, a second single-phase converter and a third single-phase converter. The novel three-phase serial modular multilevel converter HVDC converter disclosed by the invention has a low cost and can block the DC short circuit current.

Description

technical field [0001] The invention belongs to the field of high-voltage, high-power power conversion device topology and its control strategy, and relates to a novel three-phase serial modular multilevel HVDC converter. Background technique [0002] Modular multilevel converter (multilevel modular converter, MMC) is a topology of voltage source converter (voltage source converter, VSC), proposed by Marquardt and Lesnicar at the IEEE PowerTech Conference in 2002, is the latest achievement in the development of HVDC transmission technology . Compared with the two-level and three-level converter topologies, the MMC topology has many advantages: modular design, flexible changes in voltage and power levels can be realized by adjusting the number of sub-modules in series; low switching frequency, reduced losses; The output voltage waveform is very smooth and close to the ideal sine waveform, with less harmonic content, no need for large-capacity AC filters on the grid side; str...

AI Technical Summary

Problems solved by technology

However, in order to output a DC voltage of the same voltage level, the number of switching devices used in the half-bridge or full-bridge MMC system is twice or four times that of the traditional two-level VSC topology, so the high cost is a problem of the current MMC system. main disadvantage

At the same time, the short-circuit fault of the DC side is also the main problem faced by MMC at present.

In actual engineering, half-bridge sub-modules are used. When a fault occurs on the DC side, since the anti-parallel diode can still provide a path for the fault current, a three-phase short circuit occurs in the system, and the fault current cannot be cut off by blocking the converter, which seriously endangers the system. safe and stable operation of

Moreover, since there is no zero-crossing point of DC current, it is difficult to extinguish the arc, and the manufacturing process of high-voltage and large-capacity DC circuit breakers is still immature. It is still in the experimental stage and is rarely used in engineering.

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