Ripple Reduction in DTC Drives by Using a Three-Level NPC VSI

A Direct Torque Control strategy of a three-level Neutral Point Clamped inverter-fed induction machine is presented. Three-level inverters are an emerging technology and are commonly applied to high power motion drives instead of the standard two-level voltage source inverters (VSI). In three-level inverters the blocking voltage of each switch is half of the DC bus voltage, lower dV/dt is generated and the output voltage and current have lower harmonic distortion. In this paper the application of the Direct Torque Control (DTC) strategy is studied for this particular topology. In the three-level inverter the voltage selection possibilities are enhanced since more inverter states are available. In the simulation results, the Three-level DTC system shows reduction in torque ripple and harmonic distortion in the stator currents and voltages. Both features are important for applications in motion control where smooth movement and high efficiency are necessary.