Thyristor technology is inherently superior to transistor for blocking voltage values above 2.5kV, plasma distributions equal to those of diodes offering the best trade-off between the on-state and blocking voltages.
Description of IGCT
Until the introduction of newer power switches, the only serious contenders for high-power transportation systems and other applications were the GTO (thyristor), with its cumbersome snubbers, and the IGBT (transistor), with its inherently high losses. Until now, adding the gate turn-off feature has resulted in GTO being constrained by a variety of unsatisfactory compromises.
The widely used standard GTO drive technology results in inhomogenous turn-on and turn-off that call for costly dv/dt and di/dt snubber circuits combined with bulky gate drive units.Rooting from the GTO is one of the newest power switches, the Gate-Commutated Thyristor (GCT). It successfully combines the best of the thyristor and transistor characteristics, while fulfilling the additional requirements of manufacturability and high reliability.
The GCT is a semiconductor based on the GTO structure, whose cathode emitter can be shut off "instantaneously", thereby converting the device from a low conduction-drop thyristor to a low switching loss, high dv/dt bipolar transistor at turn- off. The IGCT (Integrated GCT) is the combination of the GCT device and a low inductance gate unit. This technology extends transistor switching performance to well above the MW range, with 4.5kV devices capable of turning off 4kA, and 6kV devices capable of turning off 3kA without snubbers.
The IGCT represents the optimum combination of low loss thyristor technology and snubberles gate effective turn off for demanding medium and high voltage power electronics applications.The thick line shows the variation of the anode voltage during turn-off. The lighter shows the variation of the anode current during turn-off process of IGCT.