Quasi-two-level and three-level operation of a diode-clamped multilevel inverter using space vector modulation

This study presents space vector-based quasi-two-level operation of a diode-clamped multilevel inverter which improves dc link utilisation and output voltage quality, and avoids the dc link capacitor voltage balancing problem experienced with standard multilevel operation. Beside a review of quasi-two-level operation and the capacitor voltage balancing method, the study presents a detailed discussion on the implementation of space vector modulation and the selection of switching sequence for a five-level inverter. Additionally, the condition for maximum theoretical modulation index for space vector modulation is established. A prototype five-level diode-clamped inverter is to experimentally validate the approach. Also this study extends the concept of quasi-two-level-to-three-level operation of the diode-clamped multilevel inverter in order to address the shortcomings experienced with quasi-two-level operation, such as low waveform quality and high switching losses. The validity of three-level inverter operation is confirmed experimentally on a prototype of a five-level diode-clamped inverter. The study also highlights the limitations of three-level operation of a diode-clamped multilevel inverter.