NPC - Neutral Point Clamped


The classic NPC stage features four IGBTs and six diodes. The blocking voltage is 600 V / 650 V or 1200 V. All modules are equipped with an NTC or PTC alongside the power semiconductors.


Modules with an NPC topology are used mainly in three-phase PV inverters and uninterruptible power supplies, and rarely also in frequency inverters with a high output frequency.

How it works

An NPC module is often called a three-level module.

When an NPC module is used as in inverter operation, the DC-link voltage can be converted into a variable alternating voltage and variable frequency. In contrast to a half-bridge or sixpack, an NPC topology offers an additional voltage level at the output. The potential not only jumps to DC+ and DC-; it can also have a status of 0. The inner IGBT switches are called NP (neutral point) IGBTs and the center-point of the DC-link is switched to the output. At real or active power, these are switched at just 50 Hz and thus correspond to the positive or negative sinusoidal half-wave. Usually operated at a higher 16 kHz frequency, the outer switches generate the sine wave. This requires from components half the blocking voltage capability needed for conventional topologies.

It is to be noted that semiconductors with a higher blocking voltage capability switch slower than semiconductors with lower blocking voltage capability. NPC topologies with 600 V components can therefore be operated at higher switching frequencies than 1200 V half-bridges. Furthermore, the voltage applied by three-level topology to the output filter is half the one of a two-level topology.

The MNPC module is an alternative to the NPC module. It also works with three levels at the output. Each topology has its advantages, depending on the switching frequency.

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NPC - Neutral Point Clamped