Study on the current oscillation between IGCT and anti-paralleled FRD in IGCT-MMC half-bridge

In recent years, with the rapid development of renewable energies and their connection demand with AC grids, modular multilevel converter technology (MMC) has been studied a lot. And the integrated gate-commutated thyristor (IGCT) has great potential in MMC application because of low loss, low cost and high reliability. However, there exists current oscillation between IGCT and the anti-paralleled fast recovery diode (FRD), which is caused by the changes of IGCT's anode potential during IGCT's turning off period. To explore the current oscillation mechanism, this paper extracts the stray inductances of a designed IGCT-MMC half bridge module and builds an IGCT-FRD current oscillation analyzing model using the physics based compact model of IGCT and the dynamic model of diode. The results show that greater the reverse recovery softness will cause smaller the current oscillation peak value with nearly constant cycle. As the equivalent junction capacitance of FRD increases, the current oscillation cycle and peak value both increase, while as the stray inductance increases, the current oscillation cycle increases and the peak value decreases.