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 regulator, power factor correction (PFC) and uninterrupted power supplies (UPS). It is composed of three single-phase three-leg converters with a leg shared by both load and grid sides. Suitable modelling, a pulse-width modulation (PWM) strategy based on 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 of the harmonic distortion, reducing switching stress and power losses. Simulation results are used to compare the studied configuration with a conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results are presented to validate the theoretical considerations and were obtained by using IGBTs with dedicated drives and a digital signal processor (DSP) with appropriated plug-in boards and sensors.