DTC of three-level inverter fed brushless DC motor drives with torque ripple reduction

The paper deals with the synthesis and performance analysis of the direct torque control (DTC) strategy dedicated to three-level NPC inverter (B12) fed brushless DC (BLDC) motor drives. The principle of operation of the BLDC motor fed by the B12-inverter is firstly presented with emphasis on the two-phase conduction mode and the three-phase conduction one. The DTC strategy is treated considering three different schemes, namely: (i) DTCi strategy inspired from the one developed by Takahashi in induction motor drives, (ii) DTC2 strategy that considers a vector selection table simply-reduced to the torque control with a two-phase conduction mode during sectors operation, and (iii) DTC3 strategy that eliminates the torque dips penalizing DTC2 during sector-to-sector commutations by considering the three-phase conduction mode. Simulation results, carried out considering low and high reference motor speeds, proves the high performance exhibited by the proposed DTC3 strategy.