Fault-tolerance-capability-equipped MMC sub-module structure capable of realizing DC fault self-protection, and MMC modulation method thereof

Abstract

The invention discloses a fault-tolerance-capability-equipped MMC sub-module structure capable of realizing DC fault self-protection. Current stress balance of two capacitors and eight power switch tubes in a sub-module are adjusted through redundant switch states; three level can be output at a normal mode, and the level integration of the sub-module is improved; under the condition of a locking mode, the capacitors of the sub-module are completely invested into legs, the capacitors of the sub-module are charged, a reverse electromotive force is generated, and a function of isolating DC-side faults is realized. According to the invention, when the sub-module structure is applied to an MMC-HVDC system, self-protection of the DC-side faults can be realized. Due to the symmetry of the structure, the output characteristics of sub-module structure, under the condition of the locking mode, are symmetrical about a current direction, and good symmetry helps to maintain the current stress balance of the power devices and the capacitors in the sub-module; and when the MMC sub-module structure is applied to an HCMC-HVDC system, the MMC sub-module structure is lower in conduction loss than a full-bridge sub-module structure and higher in system operation efficiency.

Description

technical field [0001] The invention belongs to the technical field of flexible DC power transmission and distribution, and in particular relates to an MMC sub-module structure and an MMC modulation method with fault tolerance capable of realizing autonomous protection against DC faults. Background technique [0002] Since the advent of Modular Multilevel Converter (MMC) in 2002, it has increasingly become a high-voltage DC (High It is one of the most promising converter topologies in Voltage Direct Current (HVDC) transmission systems. Most of the MMC-HVDC projects currently in operation adopt the Half Bridge Sub-Module (HBSM) structure, which has a small number of power devices, low system cost, and high operating efficiency. It does not have active protection capability by itself, and needs to use AC relay protection equipment to isolate faults. [0003] DC side short-circuit fault is a common fault form in DC transmission, especially in overhead lines. At present, ther...

AI Technical Summary

Problems solved by technology

The number of power semiconductor devices in the full-bridge sub-module is twice that of the half-bridge sub-module, which increases the system cost and reduces the operating efficiency of the converter; although the structure of the clamping twin sub-module is simple, it has poor fault tolerance. If the tube is damaged, the sub-module will not be able to achieve the normal output of the level, which will affect the normal operation of the entire system

Images