Power converters Modelling - NPC versus no NPC
As the name suggests, an N-level converter can synthesis N-levels of voltage to the load 

A 2 level can produce 0V and +-Vdc

A 3 level can produce 0V, +-0.5Vdc and +-Vdc

Why is this important or beneficial? Losses, EMC and breakdown and output quality

In the NPC topology each switching device is subjected to half the DC link. This results in half the switching losses (per device).

Because only half the DC link is ever switched, the dv/dt is reduced which is a benefit for EMC and long harnesses.

Likewise you can construct an inverter that blocks higher potential as each switch only sees a maximum of half DClink (GAN devices are only available in 600V so an NPC inverter can realise a 1200V inverter - NOTE there is an annoying power down case which can result in a switch experiencing FULL DClink)

Finally because the output waveform has a total of 5 steps not 3, the synthesised voltage waveform is closer to a true sine wave. If a true sine wave is needed then the needed filtering is not as harsh.



Note: there is another topology, T-type which is a 3level.