Multi-level direct torque control with imposed switching frequency and reduced ripple

A new strategy for direct torque control at imposed switching frequency (DiCoIF) is proposed. This strategy was specially designed to operate with a multi-cell (flying capacitors) inverter with any number of levels, which means it can even be used for standard two-level inverters. This approach combines the well known advantages of the multi-cell inverter with those of a DTC based strategy. It is shown that the multi-cell topology presents enough degrees of freedom to control both torque and flux with very reduced ripple and high dynamics, and also to regulate the switching frequency and flying capacitors voltages. Experimental and simulation results are presented and discussed to confirm the effectiveness of the proposed DiCoIF strategy applied both to the standard two-level inverter and to a four-level multi-cell inverter. A comparative analysis either with the classical DTC and field oriented techniques is carried out.