T. Wolbank, P. Weinmeier:
"The impact of different methods to generate Inform test pulses for sensorless control of a.c. machines on power electr";
Poster: PCIM, Nürnberg, Germany; 05-26-1998 - 05-28-1998; in: "Power Electronics, Automation, Motion, Drives and Control, Power Quality, PCIM'98", (1998), 517 - 523.

One disadvantage of field oriented control of AC-machines is the need of a mechanical sensor for determining the rotor speed/position. Omitting this speed- or position sensor saves costs and leads to a more robust drive. When realising a sensorless control scheme, the flux model has to determine the flux position only from the measured electrical quantities of the terminal voltage and current. With a fundamental model of the machine, the flux becomes unobservable at zero (fundamental) stator frequency. Therefore it is impossible to realise a stable operation at zero stator frequency. One of the sensorless control schemes, which has been verified in practical operation, is the Inform method ("Indirect Flux detection by On-line Reactance Measurement"). In induction motors and non-salient pole synchronous motors the method is based on a non-constant leakage inductance along the airgap due to the main flux of the machine. For synchronous reluctance and interior permanent magnet motors, the saliency of the rotor results in a corresponding modulation. The Inform method detects the magnetic anisotropy by evaluating the change of the stator current space phasor due to stator voltage test phasors. This test phasors have influence on the power electronic inverter as well as the performance of the machine. In this paper the influence of different realisations concerning the application of the Inform test phasors on the switching frequency and on the output current harmonics is investigated and a new inverter switching control strategy is presented, which integrates the current control and the generation of the necessary test phasors in a modified Inform current controller (ICC)