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

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 an RSHVS is usually designed with an appropriate voltage derating 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. In this article, we propose 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 that, 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 that 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 an RSHVS consisting of eight IGBTs.