Fault-Tolerant Behaviour of the Three-Level Advanced-Active-Neutral-Point-Clamped Converter

Inhalt:
Multilevel converters in medium-voltage applications reduce the cable cross-section, the voltage step size and the necessary filter effort in comparison to the conventional two-level converter. While at low-voltage level, several converters can be connected in parallel at low cost, at medium-voltage level this redundancy is missing. In case of a failure, the whole system cannot continue to operate. This paper presents a three-level converter topology as solution for medium voltage. A three-level converter based on half-bridges is divided into two partial converters, which are high-inductively coupled. A failure is limited to one half of the converter and half of the DC-link voltage remains. Redundant operation at reduced power is available. The protective inductance is determined, based on measurements on a 6.5 kV-IGBT.