The active NPC converter and its loss-balancing control

The three-level neutral-point-clamped voltage-source converter (NPC VSC) is widely used in high-power medium-voltage applications. The unequal loss distribution among the semiconductors is one major disadvantage of this popular topology. This paper studies the loss distribution problem of the NPC VSC and proposes the active NPC VSC to overcome this drawback. The switch states and commutations of the converter are analyzed. A loss-balancing scheme is introduced, enabling a substantially increased output power and an improved performance at zero speed, compared to the conventional NPC VSC.

Nomenclature

Loss coefficients.

Carrier frequency.

Fundamental frequency.

Instantaneous phase current.

RMS value of the phase current.

Modulation depth .

Power factor.

Turn-on, turn-off, and recovery losses.

Conduction losses.

DC-link voltage.

RMS value of the line-to-line voltage.

Instantaneous phase-to-neutral point (NP) voltage.

Reference voltage for carrier-based modulation.

Ambient temperature.

Junction temperature.

Outer switches and diodes .

Inner switches and diodes .

NPC switches and diodes .