Operation of a Seven-Level T-Type Active Neutral-Point-Clamped Converter with Modified Level-Shifted PWM

This paper presents novel control strategies for a seven-level (7L) T-type active neutral-point-clamped (T-ANPC) converter based on level-shifted pulse width modulation (LS-PWM) technique. Compared with classical 7L topologies, such as NPC, flying capacitor converter and cascaded H-bridge converter, the 7L T-ANPC converter can reduce the device requirements while reserving the advantages of high redundancy and low conduction losses. Furthermore, the internal switching state redundancy provides freedom to balance the flying capacitor (FC) voltage and realize the fault-tolerant operation flexibly. The control strategy with modified LS-PWM technique is developed for the T-ANPC to obtain desired outputs under normal and switch open fault modes. The proposed control strategy considers the complete balancing of dc-link neutral-point voltage and FC voltages. The feasibility of the proposed 7L T-ANPC and control strategy is evaluated by simulations and experimental tests under steady state and several typical transient operating conditions.