PROJECT TITLE :

A Generalized Natural Balance Model and Balance Booster Filter Design for Three-Level Neutral-Point-Clamped Converters

ABSTRACT:

Three-level neutral purpose clamped (NPC) inverters exhibit a natural balancing property which will self-regulate the intermediate neutral purpose voltage to [*fr1] the general dc-link voltage. However, the underlying mechanisms of this process don't seem to be well understood, its performance under numerous load conditions has not been properly explored, and the necessities and benefits of ( $RLC$) balance booster filters to enhance the natural balancing response are not clear. This paper presents a generalized model of an NPC natural balancing process that permits these problems to be explored for varied load structures and balance booster configurations (i.e., isolated wye, wye with a grounded star point, etc.). The model accurately predicts the dominant balancing time constant, identifies the harmonics that drive the balancing process, and can quantify the steady-state balance booster losses for a designed target natural balance response. Extensive simulation and experimental tests are performed to validate the theoretical model.