Reliability considerations and fault handling strategies for multi-MW modular drive systems

Shunt-interleaved electrical drive systems consisting of several parallel medium-voltage back to back converters enable power ratings of tens of MVA, low current distortions and a very smooth airgap torque. In order to meet stringent reliability and availability goals despite the large parts count, the modularity of the drive system needs to be exploited and a suitable fault handling strategy that allows the exclusion and isolation of faulted threads is required. This avoids the shutdown of the complete system and enables the drive system to continue operating. If full power capability is also required in degraded mode operation, redundancy on a thread level needs to be added. Experimental results confirm that thread exclusion allows the isolation of the majority of faults without affecting the mechanical load. As the drive system continues to run, faulted threads can be repaired and then added on-the-fly to the running system by thread inclusion. As a result, the downtime of such a modular drive system is expected to not exceed a few hours per year.