Reliability Evaluation of Three-Level Inverters

To date, many inverter topologies have been proposed in the literature with each exhibiting certain advantages and disadvantages. These inverters are however mostly proposed with their reliability indexes left unexplored. The main reason for a lack of reliability assessment might be a lack of existing quantitative techniques that can be used for computing a mathematical index for associating with the inverter topology under consideration. Without the relevant mathematical index, comparing of inverter reliability is generally impossible or merely based on qualitative reasoning, which at times is subjective to individual preferences. Aiming to address that issue on reliability assessment, this paper proposes an appropriate method based on multi-state computation, uniquely fine-tuned for inverter (or general converter) evaluation. To demonstrate its applications, the formulated method is indifferently used for computing the reliability indexes / models of existing single-phase and three-phase three-level inverters to provide a common ground for their reliability evaluation. For inverters with possibilities of raising their indexes, topological and modulation modifications are proposed with their practicality and performance verified in simulation and experimentally.