Three-Level F-Type Inverter

Abstract

Given the recently available IGBT switch modules up to 6.5 kV, 1200 A rating, the prospect of the diode-free variant topology of the three-level neutral-point-clamped (3-level T-type, NPC) inverter in certain medium-voltage applications is bright due to its small part count and low conduction losses compared to the diode-clamped NPC inverter. However, within this voltage range, the input dc voltage rating of 50% of the switches per inverter phase-leg still poses limitations to the deployment of a 3-level T-type inverter. In view of these limitations, a reconfigured four-switch per phase-leg power circuit for a 3-level inverter (F-type) is presented in this article. The common node of the bidirectional switch in the T-type inverter is explored to have only one power switch rated at input dc voltage and three switches rated at half the input dc voltage per inverter leg. This reduced voltage stress has inverter cost and loss implications. The performances and competitiveness of the three-level F-type inverter are analyzed in detail and demonstrated with a hardware prototype. Results reveal that it has the potentials of being considered a real alternative to 3-level T-type inverters for certain low- and medium-voltage applications.