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T. Wolbank, A. Moucka, J. Machl:
"A comparative study of field-oriented and direct-torque control of induction motors reference to shaft-sensorless control at low and zero-speed";
Vortrag: IEEE International Symposium on Intelligent Control, Vancouver, Canada (eingeladen); 27.10.2002 - 30.10.2002; in: "Proceedings of the 2002 IEEE International Symposium on Intelligent Control", IEEE Cat.No.02CH37395 (2002), ISBN 0-7803-7620-8; S. 391 - 396.

In modern high performance ac drives usually field oriented control (FOC) or direct torque control (DTC) schemes are applied to achieve high dynamic operation. In literature the advantages and disadvantages of the global performance of each scheme have already been treated. Recently big efforts have been made to eliminate the machines shaft sensor and thus to reduce the costs of the drive and at the same time increase the reliability. Though DTC is often designated as sensorless scheme, it has the similar problems to FOC when operated around zero flux frequency. In this paper the performance of both schemes is investigated with special emphasis to the operation around zero speed. In that operating range it is assumed nowadays, that without shaft sensor the flux position can only be determined by exploiting parasitic effects of the machine such as saturation or slotting. Sensorless schemes to estimate the spatial flux position control suffer however from a reduced accuracy in specific load ranges which degrades the performance of the drive when compared to operation with shaft sensor. On a test stand FOC as well as DTC have been realized and the flux position calculated with the use of a speed sensor has been modified with different error functions to test the reaction of both schemes on erroneous flux input values.