Comparative evaluation of modulation algorithms for neutral point clamped converters

Neutral point clamped (NPC) converters are increasingly applied in industrial drive systems as they allow the use of lower voltage devices in higher voltage applications, provide reduced output voltage THD and can develop low common mode voltage. Several distinct modulation strategies have been proposed in the past for eliminating the common mode voltage, providing low THD output voltage or reducing the neutral point current ripple. However, each of these strategies improves the performance of the converter on one metric while trading off performance in other metrics. Nearest three vector, radial state and zero common mode types of space vector modulation techniques are compared using metrics that clearly elucidate the performance tradeoffs. Analytical models, computer simulation results and experimental verification are presented.