Comprehensive analysis of voltage balancing techniques for 5L NPC converters

Abstract

The reduced capability of the 5L-NPC Inverter to balance the voltages of the four DC-bus capacitors makes this converter unattractive for real power applications. This is especially true if the load demands active power. The Back-to-Back (B2B) configuration of two 5L-NPC converters and the use of a Space Vector Modulation (SVM) that exploits the voltage balancing capabilities of the redundant switching vectors, extend the operating conditions range in which a proper voltage balance can be achieved. However, if practical modulation restrictions are considered (limitation of voltage steps, dead times, switching losses, etc.) the voltage balance cannot be achieved for all operation conditions. This paper introduces the main restrictions that should be considered for the 5L-NPC modulation strategy. The voltage balancing limits of the proposed SVM scheme are shown and additional considerations to improve the voltage balancing capability are proposed and evaluated.