A Distributed Turn-off Delay Compensator Scheme for Voltage Balancing of Series-connected IGBTs

This paper presents a voltage balancing scheme for Series-Connected IGBTs (SCIs) using a turn-off delay compensator. In SCIs, inherent synchronization challenges and parasitic capacitances lead to uneven voltage distribution and potential over-voltage conditions. Traditional time delay adjustment methods adjusting both turn-on and turn-off delays involve complex circuitry, difficult for numerous SCIs. The paper examines factors affecting voltage imbalances during turn-on and turn-off transitions, revealing that turn-off imbalances are more critical. Therefore, a straightforward approach is introduced for turn-off delay compensation, eliminating the need for high bandwidth and isolated feedbacks. Additionally, in the proposed scheme, by locally adjusting the turn-off delay time for each switch, obviating the necessity for separate command signals. Consequently, this pragmatic scheme is especially well-suited for applications where the complexity becomes a hindrance to expanding the number of series-connected switches. Simulation and experiments involving four IGBTs within a 2.4 kV system demonstrate a voltage balancing accuracy of less than 20 V.