A new direct torque control strategy for the minimization of common-mode emissions

This paper presents a new direct torque control (DTC) algorithm for induction machine drives capable of reducing the common-mode conducted emissions of the drive. It is based on the application of only odd or only even voltage vectors in each sector in which the stator flux lies. In the work, after an overview of the generation of common-mode emissions of inverter fed drives and the most employed techniques for their minimization, a simplified equivalent circuit of the common-mode path has been identified to be used in numerical simulation on the basis of experimental measurements. Then, the new DTC technique has been described and applied to an induction machine drive, both in numerical simulation and experimentally on a suitably developed test setup. Finally, results are presented and compared to those obtained with the classic DTC technique. It has been shown that this methodology is able to reduce the common-mode voltage repetition rate, and therefore the resulting common-mode currents in comparison with the classic DTC in a frequency range of about tens of kilohertz. Finally the analysis of the impact of both control techniques in terms of the current absorbed by the grid has been performed.