Investigation of Three-Phase AC–DC–AC Multilevel Nine-Leg Converter.

In this paper, a reversible multilevel nine-leg converter for three-phase applications is investigated. This topology can be applied in line voltage regulators, power factor correction devices, and uninterrupted power supplies. It is composed of three single-phase three-leg converters with a leg shared by both load and grid sides. Suitable modeling, a pulse-width modulation (PWM) strategy based on a vector approach, and a control system are developed. The proposed PWM and control strategies are suitable to balance the dc-link voltages and to optimize the harmonic distortion, reducing switching stress and power losses. The investigated configuration is compared with two conventional topologies, including a neutral-point-clamped converter and has demonstrated that it presents some advantages in terms of voltage rating of the power switches, harmonic distortion, and semiconductor losses. Computer simulations and experimental results have been carried in the same operation conditions to verify the validity of theoretical considerations. [ABSTRACT FROM PUBLISHER]