An Online Condition Monitoring Method for Series-Connected IGBTs to Avoid Cascading Failure

Abstract

The series-connected insulated gate bipolar transistors (IGBTs) have numerous applications in industry and research fields. One of the risks of the resultant series high-voltage switch (RSHVS) is the IGBTs short circuit failure. The number of the IGBTs in a RSHVS is usually designed with an appropriate voltage de-rating factor to make it resilient against a limited number of the IGBTs short circuit failures. However, by the increased number of failures, the withstand voltage of the healthy IGBTs finally violates the IGBTs' tolerable voltage in the off-state. In such conditions, a cascading failure occurs and breaks all remaining healthy IGBTs. This paper proposes a condition monitoring (CM) method to avoid cascading failure in RSHVSs. The proposed method works based on the change of the rising edge of the load current in the RSHVS turning-on time. It will be shown when some of the IGBTs in the series structure fail short, the turning-on time of the RSHVS increases. Thus, the rising edge of the current also increases which leads to the decrement of high-order harmonics magnitude. The proposed CM analyzes such harmonics and provides a constant voltage as the CM output. The performance of the proposed CM is evaluated using simulations and experiments for a RSHVS consisting of eight IGBTs.