Direct Torque Control of Induction Motors by New Multi-level Inverters

Many industrial applications require variable speed motor drives. The AC machines, especially induction types, have been widely used in such applications. In certain applications such as traction applications, speed is not the state of interest to be controlled. Instead, the torque is directly controlled, as it is seen of more importance from the load point of view. The direct torque control (DTC) is a new scheme of induction motor torque control, and is considered nowadays one of the superior strategies compared to other different schemes such as scalar or vector control techniques. The aim of this study is to present a new DTC scheme for asynchronous motors using the classical two-level six-switch voltage source inverter (VSI) when controlled by an innovated 150o conduction-mode. This switching-mode results in a novel space-vector-diagram (SVD) for the two-level inverters, consequently enables new switching-tables for the DTC scheme. The new DTC scheme quietly improves the motor performance compared to the classical method. New three-level voltage source inverter, that combines some desirable features of two- and three- level inverters, is introduced.