Recovering Partial Three-Level Operation in a T-Type Inverter with Fault Management Redundant Unit

A redundant unit has been utilized in prior work for a T-type three-level inverter to handle multiple open-circuit faults, but the output was limited to two levels. In this article, equivalent switching state and improved virtual vector methods are proposed to complement switching states and provide better fault-tolerant performance. Under fault scenarios, equivalent replacement of unreachable switching states can be used to generate the target line-to-line voltages. If the replacement cannot be achieved by equivalent switching states, a virtual vector with redundant capability is employed to support two- and three-level modulations at the output. The rearranged switching sequences can be formed by employing virtual vectors and existing vectors. In addition, by reconstructing the virtual vectors, a balancing method is adopted to eliminate neutral point voltage offset in cases of multiple faults. Experimental tests verify the effectiveness and feasibility of the proposed method.