Power Electronics Converter Topologies
Neutral-Point Clamped (NPC)

Multilevel converters have emerged in recent years as a very important alternative in the area of high-power medium-voltage energy control. The need for an increase in the power level of industrial applications is especially important in high power applications such as high power AC motor drives, active power filters, and renewable energies.

The term multilevel refers to the three-level topologies and above. The increase in the number of levels in the converter leads to harmonic distortion. Yet, as the number of levels increases so does the control complexity.

The most common multilevel topologies include the Neutral Point Clamped (NPC) converter (in its 3-Level version), the Active Neutral-Point Clamped (in its 3-Level and Multi-level versions, the T-Type, the Multicell topologies such as the Flying Capacitor (FC), the Stacked Multi-cell Converter (SMC).

Electrical schema

power converter topologies 3-level neutral point clamped NPC

Example of a 3-level Neutral-Point Clamped (NPC)

Conversion stage

  • DC/DC mono and bi-directional

  • DC/AC mono and bi-directional

Number of levels

  • Typical: 3
  • Max: 3

Intellectual Property

Initial patent US4270163A expired

Notes

Custom modules look for compensating:

  • Poor distribution of losses by using different switches
  • Large commutation loops by adding snubber diodes or capacitors

Typical application and trends

  • Medium voltage drive up to 3.3kV
  • UPS up to 690VAC
  • Solar up to 900VDC
  • Electric Vehicle

Advantages

  • Standard and custom modules available

Drawbacks

  • Unbalanced powerswitch losses (poor distribution)
  • Large commutation loops

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