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Active neutral-point-clamped converter adds open-circuit fault-tolerant (OCFT) capability compared with the widely used original neutral-point-clamped (NPC) topology. However, such capability is hard to utilize due to difficulties in pulse-width modulation (PWM) design and the randomness of failure points, particularly in high-level converters. Current research mainly focused on low-level topologies with a limited number of fault scenarios; moreover, the analysis and design are performed in a nonsystematic way. In this article, the OCFT operations of active NPC (ANPC) converters with multiple fault switches are investigated and the systematic PWM design process is proposed. First, different matrices are proposed for the ANPC converters to capture the complicated topology information and achieve an exhaustive analysis of the topological redundancy. Then, a step-by-step process is proposed to derive the suitable OCFT PWM patterns. The five-level ANPC converter is investigated as an example. Its experimental results validate that the proposed approach can 1) properly predict the behavior of converters systematically so that the tolerable faults and intolerable can be identified during the design procedure, and 2) the inherent fault-tolerant capability of the five-level ANPC converter can be guaranteed through the proposed method, and 3) multiswitch open-circuit faults can be easily dealt with by implementing suitable carrier-based PWM schemes. [ABSTRACT FROM AUTHOR]

Controlling a three-level neutral-point-clamped (3L-NPC) inverter-fed permanent-magnet synchro-nous machine (PMSM) drive is a challenging task, especially when the dc-link voltage is unbalanced. The unbalanced dc-link voltages, which are with some of the voltage vectors varying in magnitude and phase, lead to highly distorted stator current. In this article, a two-stage model predictive control (MPC) is proposed for the 3L-NPC inverter-fed PMSM drive. In the proposed MPC method, control of the 3L-NPC inverter is decoupled into two stages. In the first stage, three switching states are determined by small hexagon selection using finite control set MPC. The rest switching states are controlled using the multiple vector MPC in the second stage. In the two-stage MPC, the number of switching state evaluations can be significantly reduced, and the nonlinearity caused by the unbalanced dc links can be included in the duty cycle optimization process, leading to improved output current quality under unbalanced dc links and reduced computational burden. Moreover, the output switching frequency is fixed due to the employment of the multiple vector MPC. A thorough experimental evaluation of the proposed MPC method with the deadbeat control with the pulsewidth modulation strategy has been conducted to validate the superiority of the proposed method. [ABSTRACT FROM AUTHOR]