Research on fault characteristic of modular multilevel converter

Abstract

Along with China proposes to build a new energy power system, various DC transmission technologies have been extensively studied. As the most serious fault type of the DC transmission system, permanent DC bipolar short-circuited fault is easy to cause converter damage. Modular multilevel converter can be used in the DC power transmission and distribution systems because of its modular design and strong ability on handling fault. When permanent DC bipolar short-circuited fault occurs, the research on fault characteristics of modular multilevel converter can offer important support for current-limiting control of converters and relay protection of power system. By analogy with the fault evolution mechanism of two-level converter, the equivalent zero-crossing voltage of sub-module capacitance is defined, and the fault evolution mechanism of modular multilevel converters can be obtained. The expressions of the fault characteristic parameters including the equivalent zero-crossing voltage of the sub-module capacitance, the DC steady short-circuited current, the peak value of the DC short-circuited current and their difference, and the peak time of the DC short-circuited current were deduced. By the way of analysis and simulation, the influence of the main circuit parameters in MMC on the characteristic variables with short-circuited fault can get the regularity, it can provide the theory basis for the current-limiting control and relay protection.

Keywords

• Modular multilevel converter
• Short-circuited fault
• Fault characteristic