Fault tolerant-topology and controls for a three-level hybrid neutral point clamped-flying capacitor converter

This study details a three-level hybrid fault-tolerant converter. The definition of an original decoupling solution between the fourth flying capacitor (FC) leg and the three neutral point (NP) clamped-based phases overcomes topology hybridisation issues. Under normal conditions, a control strategy of the FC-based leg leads to a converter NP voltage balance, and decreases the DC side capacitors’ volume and cost. Under fault conditions, the presented fault isolation and converter reconfiguration strategies generate a post-fault converter, which is able to operate safely with the added FC-based leg. The proposed topology is an interesting trade-off between converter fault-tolerant capability and its complexity and offers the ability to be simply reconfigured and controlled in the case of switch fault occurrence. Two operation modes under fault conditions are presented and their performances are shown and discussed through simulation results and first experimental tests.