Enhanced Four-Level Active Nested Neutral Point-Clamped Inverter

Abstract

The classical four-level nested neutral point-clamped (4L NNPC) inverter-leg is a hybrid of the flying-capacitor and diode-clamped 4L-inverter-leg configurations. Though uniform reduced voltage stress (1/3 of input voltage) on constituting switches is evident in the 4L NNPC inverter-leg, trails of the drawbacks of the diode-clamping concept still exist. With the significantly rated off-the-shelf IGBT switch modules (6.5 kV, 1200 A), chances of deployment of the newly evolved Four-Level Nested T-Type inverter (4L NTTI) in certain applications is high. Compared with the classical 4L NNPC inverter, 4L NTTI involves a smaller number of power switches and low conduction losses. However, in 4L NTTI, two of the six active switches have a blocking voltage rating of 2/3 of the input voltage. Considering this limiting topological feature in 4L NTTI, a six-switch inverter-leg for the four-level active neutral point-clamped (4L ANNPC) inverter is presented in this paper. In the proposed 4L ANNPC inverter-leg, only one switch has a voltage stress of 2/3 of the input voltage. This ameliorated voltage stress translates to low-cost and -loss inverter implementation. The operational characteristics and competitiveness of the 4L ANNPC inverter are analyzed in detail and demonstrated with a prototype.