Comparison of two modulation strategies for a three level inverter synchronous reluctance motor (SynRM) drive

In this paper, two modulation strategies for a three level neutral point clamped inverter SynRM drive are compared. The inverter uses two different algorithms called Mod-1 and Mod-2 for balancing the two dc bus capacitor voltages (suppression of the neutral point voltage). These modulation strategies are of the nearest three vector (NTV) family. Mod-1 chooses certain vector states to suppress the neutral point (NP) voltage ripple, whereas Mod-2 makes use of the inverter vector state´s dwell time. The parameters of interest are the torque ripple, the neutral point voltage ripple and the inverter efficiency. The inverter was operated at a switching frequency of 10 kHz. The SynRM core losses were independent of the two modulation strategies, though lower torque ripples and better power quality were registered on Mod-2 strategy. Mod-1 strategy had 18% higher inverter efficiency during transient operation. Mod-2 strategy had 11% more NP voltage ripple during transient operation. The Mod-1 strategy supressed the NP voltage ripple throughout the machine´s operation.