52.

D. Gebler and J. Holtz, "Identification and compensation of gear backlash without output position sensor in high-precision servo systems" in IECON '98. Proceedings of the 24th Annual Conference of the IEEE Industrial Electronics Society (Cat. No.98CH36200), 1998, pp. 662-666 vol.2.

Abstract:
High-performance position control can be improved by the compensation of gear backlash. This paper presents a compensation method that does not need an output position sensor. In the first section, two different methods of on-system backlash identification are described. One method is based on dynamic reaction to a small torque impulse injected by the motor, while the other analyses the change of torque at the end of the backlash dead zone in a quasi-stationary trajectory. The second section of the paper deals with backlash compensation. Based on the identified value of backlash, the angular error of the output shaft is reduced. A self-learning time-optimal control method is described. Experimental measurements demonstrate the excellent performance and accuracy of the compensated system.

51.

S. Soter, "Kosten- und Wirkungsgradoptimierung eines Wechselrichters mit Einzeltransistoren (MOSFET) am Beispiel eines photovoltaisch versorgten Inselsystems" in 13. Symposium Photovoltaische Solarenergie, 1998.

50.

J. Holtz, "Sensorless position control of induction motors-an emerging technology" in IECON '98. Proceedings of the 24th Annual Conference of the IEEE Industrial Electronics Society (Cat. No.98CH36200), 1998, pp. I1-12 vol.1.

Abstract:
Concepts for the sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incorporated as periodic variations of magnetic saliencies in various ways. The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain frequency components that depend on the rotor position. Models of the rotor saliency serve to extract the rotor position signal using phase-locked loop techniques. A different approach makes use of the parasitic effects that originate from the discrete winding structure of a cage rotor. It has the merit of providing high spatial resolution for incremental positioning without sensor. The practical implementation of sensorless position identification, and of a high-accuracy position control system are reported.

49.

J. Holtz, "Sensorless position control of induction motors. An emerging technology" in AMC'98 - Coimbra. 1998 5th International Workshop on Advanced Motion Control. Proceedings (Cat. No.98TH8354), 1998, pp. 1--14.

Abstract:
Concepts for sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incorporated as periodic variations of magnetic saliencies in various ways. The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain frequency components that depend on the rotor position. Models of the rotor saliency serve to extract the rotor position signal using phase-locked loop techniques. A different approach makes use of the parasitic effects that originate from the discrete winding structure of a cage rotor. It has the merit of providing high spatial resolution for incremental positioning without sensors. The practical implementation of sensorless position identification, and of a high-accuracy position control system are reported.

48.

J. Jiang and J. Holtz, "Accurate estimation of rotor position and speed of induction motors near standstill" in Proceedings of Second International Conference on Power Electronics and Drive Systems, 1997, pp. 1-5 vol.1.

Abstract:
It is demonstrated by numerical analysis that the leakage inductance as seen from the stator windings of standard induction motors varies with the rotor position angle. The effect can be exploited to extract the rotor position, and speed, from measured stator voltages. The extraction algorithm is incorporated based on a modification of the pulsewidth modulator. Experimental results demonstrate position measurement with good noise rejection at any speed including standstill.

47.

M. Ogasa, J. O. Krah and J. Holtz, "Harmonic compensator for 50-Hz fed AC railway vehicles" in Proceedings of Power Conversion Conference - PCC '97, 1997, pp. 57-62 vol.1.

Abstract:
AC railway vehicles controlled by PWM line-side power converters inject harmonic current into the feeding overhead line. This causes problems such as resonance expansions which produce malfunctions or overcurrents at substations and electromagnetic interference with signalling systems. Normal active filters only shift the harmonic frequencies to a higher range. A novel harmonic compensator produces an exact counter-MMF of which in the main transformer main flux is then sinusoidal. Experimental results from a small model of a Japanese AC railway vehicle are described. Especially the 3-4 kHz frequency range that coincides with the signalling band harmonic currents are quite well suppressed. From the result, this novel compensating method appears promising for any 50 Hz-fed PWM controlled AC railway traction system.

46.

J. Holtz, J. Jiang and H. Pan, "Identification of rotor position and speed of standard induction motors at low speed including zero stator frequency" in Proceedings of the IECON'97 23rd International Conference on Industrial Electronics, Control, and Instrumentation (Cat. No.97CH36066), 1997, pp. 971-976 vol.2.

Abstract:
The total leakage inductance as seen from the stator windings of standard induction motors varies with the rotor position angle. The effect is exploited to extract the rotor position, and speed, from measured stator voltages. The extraction algorithm is incorporated based on a modification of the pulsewidth modulator. Experimental results demonstrate accurate position measurement at high resolution and high bandwidth at any speed including standstill. Preliminary results of a sensorless vector controlled AC drive system are presented.

45.

H. Pan, L. Springob and J. Holtz, "Improving the start and restart behavior through state recognition of AC drives" in Proceedings of Power Conversion Conference - PCC '97, 1997, pp. 589-594 vol.2.

Abstract:
The paper presents control strategies for abnormal operating conditions of AC motor drive systems. These improve the total performance as well as the ruggedness of the system. Two methods to start a rotating motor through state recognition are described. Two cases are distinguished according to whether the back EMF exists or not. In either case, normal operation can be reestablished as fast as possible on return of the power supply following a power interruption. Discussions and experimental results are presented for both failure conditions, based on V/f control and on sensorless field oriented control.

44.

J. Holtz and L. Springob, "Identification and compensation of torque ripple in high-precision permanent magnet motor drives", IEEE Transactions on Industrial Electronics, vol. 43, no. 2, pp. 309--320, 1996.

Abstract:
Permanent magnet synchronous machines generate parasitic torque pulsations owing to distortion of the stator flux linkage distribution, variable magnetic reluctance at the stator slots, and secondary phenomena. The consequences are speed oscillations which, although small in magnitude, deteriorate the performance of the drive in demanding applications. The parasitic effects are analyzed and modeled using the complex state-variable approach. A fast current control system is employed to produce high-frequency electromagnetic torque components for compensation. A self-commissioning scheme is described which identifies the machine parameters, particularly the torque ripple functions which depend on the angular position of the rotor. Variations of permanent magnet flux density with temperature are compensated by on-line adaptation. The algorithms for adaptation and control are implemented in a standard microcontroller system without additional hardware. The effectiveness of the adaptive torque ripple compensation is demonstrated by experiments.

43.

J. Holtz, "On the spatial propagation of transient magnetic fields in AC machines", IEEE Transactions on Industry Applications, vol. 32, no. 4, pp. 927--937, 1996.

Abstract:
AC motors have proliferated as the most important machine type used in variable speed drive systems. The dynamic analysis and description of revolving field machines is supported by well-established theories: Park's transformation (1929), and the space vector theory by Kovacs and Racz (1959). Yet some inconsistencies with the theory of dynamic systems exist. First, the machine eigenvalues suggest the existence of two damped oscillators. Second, it appears unsatisfactory that the respective eigenfrequencies change with the velocity of the reference frame. This contradicts the common understanding according to which the eigenfrequency is an inherent system property. A clarification is reached using a novel approach for dynamic AC machine analysis. The approach is based on complex state variables. It permits relating a transient condition to the propagation processes in the space of distributed magnetic fields. The formal analysis constitutes an extension to the space vector theory and to the theory of dynamic systems.