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Short circuit failure mode (SCFM) of IGCT under extreme failure is of vital importance in MMC-HVDC system. Due to the sealing housing package of IGCT, the short circuit mechanism is hard to be clarified. Considering this limitation, the current density changes in IGCT with different failure modes are studied in a built integrated test system with placed magnetic sensor array and thermal couple array. Then the short circuit mechanism of failed IGCT is proposed based on the experiment results. IGCT with turn off failure performs self-triggering effect due to the focused short current and increased temperature in the intial destruction area, which is usually located in a single position of the outer cathode rings. While IGCT with surge current failure shares the short current among multiple initial destruction areas, which are usually distributed evenly. SEM picture and EDX analysis show that the formed conducting alloy has spread into the molybdenum plate deeply and the phenomenon of atom diffusion (molybdenum, silicon and aluminium) near the interface is observed. Finally, long term short circuit tests of more than 12h with both turn off failure and surge current failure under 3000A prove the stable short circuit failure mode of IGCT.

The integrity of housing and feature of short circuit is hardly guaranteed for traditional power devices under overvoltage breakdown with following high surge energy. Thus, extra bypass thyristor is needed to achieve stable overvoltage bypass protection for submodules in modular multilevel converters at present. In this article, a novel controlled punch-through IGCT (CP-IGCT) is presented. Based on the punch-through breakdown principle instead of avalanche breakdown principle, the device can achieve breakdown at design voltage with uniformity, thermal stability, and robust package rupture-resilience. As a consequence, no extra sacrificial device is necessary. The fabricated sample proves a stable breakdown at 4000 V and a robust short-circuit feature after energy release of a 18 mF capacitor under 4500 V.

Integrated gate commutated thyristor (IGCT) has low loss, low cost, and high reliability in the application of modular multilevel converter (MMC). However, due to the special turn- off process of IGCT, the commutation transient is very different for IGCT in MMC. This letter reveals a current oscillation phenomenon of MMC based on IGCT and fast recovery diode (FRD). Especially, this oscillation effect becomes apparent when the FRD with high surge current capability is employed in MMC because of high junction capacitance and high stray inductance, which will threaten the safe operation of the system. This letter analyzes the current oscillation mechanism and gives the current oscillation modeling. In addition, through detailed tests under various stray inductances, the specific stray inductance range that can cause large current oscillation is obtained and an optimized inductance parameter of IGCT-MMC is proposed. The experiments show that the safe operation area of IGCT in MMC can be guaranteed maximally with the optimized parameter.

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.

The performance of solid-state dc circuit breaker (SS-DCCB) is mainly determined by the on -state feature of power device. In this article, an optimized low on -state voltage integrated gate-commutated thyristor (LO-IGCT) for SS-DCCB is developed. First, the impacts of device parameters, including base length, carrier lifetime, and emitter injection efficiencies, on on -state voltage are presented. The boundary conditions raised by blocking voltage and safe operation area (SOA) are analyzed. Based on that, a three-step blocking-SOA-emitter optimization routine is proposed. Then, the optimization methodology for doping profiles in different regions, especially in n -drift, n buffer, p + base, n + emitter, and p + emitter regions, is presented. The optimal values are derived with theoretical deduction or numerical calculation. After that, based the optimization result, samples of LO-IGCTs are fabricated and tested. The fabricated LO-IGCT sample shows a blocking voltage capability over 4500 V and an on -state voltage of 1.11 V at the current of 2000 A. The commercialized IGCT and IGBT optimized for high-frequency applications exhibits 1.23 and 1.85 times the on -state voltage under the same test configuration.