An Improved Structure of Modular Multilevel Converter with DC Fault Clearing Capability

Abstract

The invention discloses an improved structure of a modular multi-level converter with direct current fault clearing capability. On the basis of the double thyristor method, an acceleration current limiting module is connected in series in each bridge arm of the MMC; the system operates normally. At the same time, all thyristors are in the off state, and the IGBTs in the acceleration current limiting module are always on; and all thyristors are turned on, preventing the AC side power supply from feeding the fault current to the DC fault point; at the same time, all IGBTs in the acceleration current limiting module in the six bridge arms are turned off, and the acceleration current limiting resistor Rc is put in to accelerate the fault isolation speed and prevent AC side overcurrent. The present invention is suitable for all types of DC faults, increasing the protection range; at the same time, it accelerates the decay rate of fault current, greatly shortens the time required for fault isolation; reduces the overcurrent borne by the AC side, and greatly reduces the overcurrent hazard of the AC side.

Description

technical field [0001] The invention relates to the field of power system protection and control, in particular to a DC fault processing method. Background technique [0002] Fast DC fault isolation is a key technology in the development of flexible DC systems. When a DC fault occurs in the flexible DC system, the fault current of the whole system rises sharply, seriously endangering the safe and reliable operation of the system. However, none of the existing converters can realize the self-clearing of the DC fault, and relevant measures must be taken to remove the faulty line. However, since the fault current does not have a natural zero-crossing point during a DC fault, it is difficult to extinguish the arc of the DC circuit breaker. Therefore, the technology of large-capacity DC circuit breakers is far from reaching the level of commercial application. Therefore, a large number of scholars at home and abroad have focused on the converter structure and corresponding cont...

AI Technical Summary

Problems solved by technology

However, because the double thyristor method converts the fault on the DC side into a three-phase short-circuit fault on the AC side, it will cause long-term overcurrent on the AC side; at the same time, the fault current is naturally attenuated according to the resistance component in the DC fault circuit, so its fault isolation speed Slows down as the fault gets closer, especially for metallic faults near the converter outlet, taking a long time to isolate the fault

In summary, the above-mentioned double thyristor method has the disadvantages of insufficient protection range and limited protection fault types, so corresponding improvement measures must be taken to solve the above-mentioned deficiencies in practical engineering applications

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