Comprehensive Analysis, Design and Experiment of Shoot-through Faults in MMC Based on IGCT for VSC-HVDC

Modular multilevel converter (MMC) based on integrated gate commutated thyristor (IGCT) with high reliability, low cost, and voltage drop is a promising choice for high-voltage dc transmission based on the voltage-source converter. This article gives a comprehensive analysis, design, and experiment of shoot-through faults in IGCT-MMC. First, the designed structure of the submodule based on the IGCT (IGCT-SM) is introduced and an equivalent circuit is established with the accurate estimation of the stray inductances. Then, the failure processes of devices and the behavior of the clamping diode are discussed in detail. Meanwhile, the mechanical stress of the connecting copper bar is analyzed during shoot-through faults. After that, an experimental platform is built for performing the shoot-through faults. Both tests with switching action and without switching action are carried out under the dc-link capacitor and voltage with 10 mF and 2.5 kV. The results show that although IGCT cannot turn off the fault current, it can withstand the fault current. The whole structure maintains stable without any cracked housing package or copper bars under the surge current of 266 kA/0.40 ms. The 24-h short-circuit test under 3.15 kA shows that failed IGCT has an extremely low on -state voltage of not more than 1.2 V and is suitable for bypassing the faulty submodule when a destroyed shoot-through fault occurs.