Different Methods for Direct Torque Control of Induction Motor Fed From Current Source Inverter

Two different methods for direct torque control (DTC) of induction motor fed from current source inverter (CSI) is analyzed in the paper. The first one is derived from well-known DTC strategy developed for voltage inverter drives. This type of control basically uses hysteresis type controllers for torque and flux. In CSI drive there is only one controller used for torque control loop. The problems that arises in such a drive is significant torque pulsations due to the nature of CSI and occasional speed drops because of variable switching frequency. The other DTC method, proposed in the paper, is based on constant switching frequency with modification of the inverter optimal switching table. Further improvements are reduced number of sensors since all measurements are performed in DC link only and in flux estimator. Both simulation and experimental results shows that this algorithm has better performance without problems that exist in the same drive with torque hysteresis comparator. Finally, proposed method is simpler for implementation in a real drive without rotational transformation and parameter dependences that exist in vector control of the same drive. Key-Words: DTC, hysteresis comparator, constant switching, CSI, induction motor