Modulation Methods for 3L-NPC Converter Power Loss Management in STATCOM Application

The uneven power loss among the semiconductor devices is one critical issue of the three-level neutral-point clamped (3L-NPC) converter, which may limit the system power capacity and degrade the reliability. Besides, different operating conditions will result in different loss distribution profiles. Among the different operating conditions, the case with low power factor and high modulation usage, which is common in the static synchronous compensator (STATCOM) application, has not been paid much attention in the literature. In this paper, the power loss distribution under this condition is theoretically analysed. And a novel carrier-based modulation technique is proposed to achieve power loss redistribution. The loss distribution under the proposed modulation technique is more even, and the loss of the most stressed device can be reduced. Besides, an active neutral-point (NP) voltage balancing control strategy is also proposed based on the proposed modulation scheme. The power loss redistribution and NP voltage control performance are both verified through simulation.