Improvements in Direct Torque Control of Induction Motor Supplied by CSI

Improvements in direct torque control of induction motor supplied by current source inverter are proposed in the paper. The flux estimator uses simple integrator and its error is compensated by EMF offset estimator. The stator current and voltage, used for EMF calculation, are determined by a reconstruction from DC link measurements, known characteristics of the inverter semiconductors and the current states of the inverter switches. The rectifier is controlled by a PI current controller as inner control loop of rotor flux controller. The rectifier current reference is resolved from the torque and rotor flux references in the similar way as in the standard vector control scheme to obtain fast DC link current response at all speeds. For the torque control, improved current switching-vector table is used, without hysteresis control that produces higher torque ripples. Simulation and experimental results are provided to confirm the performance of the proposed control algorithm