Dynamic Voltage equalization means that during the process of switching on and off, the triggering capability of each switch is different, the manufacturing process of IGBT is different, and even the switching time or performance of the same IGBT from the same manufacturer is different, these reasons cause the switching speed of IGBT is not the same in the process of switching. If the voltage of two IGBT in series is certain, then the voltage of the first open IGBT will drop first, after the opening of that IGBT is bound to bear almost all the voltage. It's the same thing when it's turned off. This is the problem of dynamic voltage equalization when IGBT is running in series.