# Power converters Modelling - NPC versus no NPC

I am trying to simulate a three-phase inverter in Matlab/Simulink.

So far I figured out that in the Simulink library there are two types of inverters. The first one is illustrated in the figure below and its called "Universal Bridge" The second type of converter is called "Three-level neutral point clamped (NPC) power converter" and you can see it below. The main difference between the two topologies is that in the NPC converter there is one more output at the DC side. I have read that we can use this output to create one more voltage level. Also, the design methodology and the control techniques are pretty much the same.

So, I would like to ask if there are any more differences and why should I select the one topology over the other.

## 1 Answer

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.