Oscillation analysis of an Active Gate Control circuit for series connected IGBTs

A Quasi Active Gate Control (QAGC) circuit provides an effective way to control static and dynamic voltage sharing to series connected IGBTs. However, different circuit parameters such as balancing capacitors, parasitic inductances, and gate resistances may influence the oscillatory stability of the power semiconductor switches during commutation. This paper presents an analysis of the small signal model of the QAGC circuit to determine the stability and explain the occurrence of high frequency oscillations during active operation of the circuit. The paper covers the application of participation factor and eigenvalue sensitivity analysis to establish circuit design criteria to ensure a stable operation. It is found that most oscillation modes can be improved with a suitable choice of the circuit elements such as gate resistors and balancing capacitors.