Analysis of capacitor voltage and boost vector in neutral-point-clamped converter and H-bridge converter

In steady states, converter is normally operated in the range of 0.7∼0.8 [p.u] of modulation index. Even though zero vectors are not imposed to high modulation index, DC-link voltage is constant. It means that there exists another boost vector except for zero vectors among several vectors in 3-level converter. This paper has examined the principle of boost and investigated the difference between another boost vector and zero vectors in 3-level converter. In addition, this paper has analysed and compared capacitor voltage of NPC and H-bridge converter. It proposed the calculation method for the voltage ripple and charging current of each capacitor and dealt with voltage balance problems of each link capacitor, which are associated with the switching state and the position of reference voltage vectors. The proposed strategy and comparison are confirmed by simulation.