2.1 Multilevel Diode Clamped/Neutral Point Inverter,
NPCMLI
According to patents the rst multilevel inverter (MLI) was designed in 1975 and it was
a cascade inverter (cascaded inverters will be presented in a later chapter) with diodes
blocking the source. This inverter was later derived into the Diode Clamped Multilevel
Inverter, also called Neutral-Point Clamped Inverter (NPC) [2], see Figure 2.1. This
topology is, as can be seen from the gure, based of the same principal as the before
mentioned three-level inverter in Figure 1.4.
In the NPCMLI topology the use of voltage clamping diodes is essential. A common
DC-bus is divided by a even number, depending on the number of voltage levels in the
inverter, of bulk capacitors in series with a neutral point in the middle of the line, see
the left part of Figure 2.1. From this DC-bus, with neutral point and capacitors, there
are clamping diodes connected to an m