Direct Calculation of SVPWM Switching Sequence for Reconfigurable N-Level Inverter in Propulsion Applications

Multi-level inverters (MLIs) have shown popularity among medium voltage marine drives, especially as they allow for increased reliability through reconfiguration. Many of today's voltage source inverters (VSI) utilize space vector pulse width modulation (SVPWM) compared to sinusoidal PWM (SPWM) due to the advantages of SVPWM in providing increased modulation index. Today's MLIs are limited in the number of levels for various reasons. This includes the ability to stack a large number of switches and coordinate their turn on/off transients, availability of control platforms that provide enough PWM channels, and ability to produce large space vector maps. This paper's main focus is to create a method for direct calculation of the switching sequence for neutral point clamped (NPC) inverters, for any N-level inverter, which is essential when MLIs are reconfigured for different levels to mitigate semiconductor switch faults. Calculation of the desired vertices to achieve a certain voltage vector is purposed through a novel projection and mapping of the reference vector in the space vector diagram.