A fault tolerant modulation scheme for a hybrid multilevel inverter in the event of open-switch fault

With ever-increasing renewable power penetration, the reliable operation of grid interfaced inverter is an important criterion. The availability of a grid-connected multi-level inverter is relied upon the correctness of identifying faulty switch, if any, during operation and implementation of a fault-tolerant modulation technique to run the inverter without tripping off even under faulty conditions. Although having a large number of switches in a multi-level inverter throws challenges for the detection and localization of faults, it is a boon because power can still flow through alternative paths. In pursuit of this objective, this paper utilizes a T-type based hybrid multi-level topology where certain faulty conditions are created. The proposed fault detection scheme begins with the fast identification of faulty phase, achieved by monitoring the absolute phase error variable derived from normalized phase currents. Subsequently, the localization of faulty switch is fulfilled by intricate analysis of several current and voltage measurements. Notably, the proposed scheme does not need additional sensors to carry out all of these, where finally, a carrier-based fault tolerant scheme is devised to encounter open switch faults. The effectiveness and feasibility of the proposed scheme are evaluated by simulation studies followed by experiments on a seven-level inverter prototype.