Simulation on the Active Voltage Balancing of Series Connected IGBTs by Monte Carlo Analysis

This article presents the dispersion of the elements influencing the active voltage balance of series-connected IGBT devices. The dynamic voltage is inconstant when the solid switches turn off. Because of the higher induction voltage of the stray inductance during the load-short, this phenomenon is the worse. By the analysis of Monte Carlo simulation, it can be found the clamp diodes in gate-driving circuit, the capacitors in the RCD snubber circuit, and the resistors in trigger or snubber circuit all affect the active voltage balance. And the parameters of the clamp voltage of the zener diodes affect significantly the transient voltage balance of series-connected IGBTs. Slight differences of a plurality of IGBTs in the transient voltage balancing can be accumulated in a particular IGBT. The more IGBTs are, the serious this case is. Clamp voltage differences of diodes are generally five percent, but voltage differences across by the 48 IGBTs in series are more than four times. According to the in-depth analysis, the diode clamp voltage difference can cause the gate turn-off delay difference. It is one of the key factors occurred the dynamic voltage imbalance.