Veröffentlichungen
- 44.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.
ISBN: 0197-2618
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. - 43.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. - 42.H. Pan, J. Jiang and J. Holtz, "Decoupling control and parameter identification of field-oriented induction motor with saturation" in Proceedings of the IEEE International Conference on Industrial Technology (ICIT'96), 1996, pp. 757--761.
Abstract:
A new decoupling control and self-commissioning parameter identification scheme for the PWM-inverter-fed asynchronous motor with saturation is presented. The modification of the field-oriented control model is considered with respect to rotor-flux-oriented control, while the nonlinear magnetizing curve is expressed as a function of the magnetizing current of the main flux path. The control model and the magnetizing curve are bridged through the inherent relationship between the rotor flux and the airgap flux. The complex signal flow graphs indicate that the dynamic structure of AC machines are not changed with magnetic saturation effects. The nonlinear magnetizing curve is estimated from a transient voltage caused by an ejected constant stator d-axis current. Experiment results indicate that the vector control of induction motor with saturation can be finely realized with the proposed model, on the basis of the recognized magnetizing characteristics. - 41.J. Holtz, "The representation of AC machine dynamics by complex signal flow graphs", IEEE Transactions on Industrial Electronics, vol. 42, no. 3, pp. 263--271, 1995.
Abstract:
Induction motors are modeled by nonlinear higher-order dynamic systems of considerable complexity. The dynamic analysis based on the complex notation exhibits a formal correspondence to the description using matrices of axes-oriented components; yet differences exist. The complex notation appears superior in that it allows the distinguishing between the system eigenfrequencies and the angular velocity of a reference frame which serves as the observation platform. The approach leads to the definition of single complex eigenvalues that do not have conjugate values associated with them. The use of complex state variables further permits the visualization of AC machine dynamics by complex signal flow graphs. These simple structures assist to form an understanding of the internal dynamic processes of a machine and their interactions with external controls.{\textless}{\textgreater} - 40.J. Holtz, "State of the art of controlled AC drives without speed sensor" in Proceedings of 1995 International Conference on Power Electronics and Drive Systems. PEDS 95, 1995, pp. 1-6 vol.1.
Abstract:
The operation of speed controlled AC motor drives without mechanical speed or position sensors requires the estimation of internal state variables of the machine. The assessment is based exclusively on measured terminal voltages and currents. Low cost, medium performance sensorless drives can be designed using simple algebraic speed estimators. High-performance systems rely on dynamic models for the estimation of the magnitude and spatial orientation of magnetic flux waves in the stator or in the rotor. Open loop estimators and closed loop observers differ with respect to accuracy, robustness, and limits of applicability. The overview in this paper uses signal flow graphs of complex space vector quantities to give an insightful description of the physical and mathematical systems used in sensorless control.{\textless}{\textgreater} - 39.J. Jiang and J. Holtz, "Speed sensorless AC drive for high dynamic performance and steady state accuracy" in Proceedings of IECON '95 - 21st Annual Conference on IEEE Industrial Electronics, 1995, pp. 1029-1034 vol.2.
Abstract:
Controlled speed sensorless AC motor drives have reached a stage of development permitting good dynamic performance above 3{%} of rated speed. However, the accuracy of the rotor speed estimation under load remains sensitive to parameter errors of the internal machine model. This paper presents an approach that ensures high steady-state speed accuracy in addition to high dynamic performance. To eliminate the speed estimation error, the machine parameters are adapted online, based on the evaluation of rotor slot harmonic effects. A stator flux oriented control scheme is implemented in a digital signal-processor system to demonstrate the robustness of the speed estimation to parameter variations. Experimental results demonstrate that the control system advantageously combines high dynamic performance with accuracy of speed estimation. - 38.J. O. Krah and J. Holtz, "Total compensation of line-side switching harmonics in converter-fed AC locomotives", IEEE Transactions on Industry Applications, vol. 31, no. 6, pp. 1264--1273, 1995.
Abstract:
PWM controlled line-side power converters of modern AC traction locomotives inject harmonic currents into the feeding overhead line. This causes problems of electromagnetic interference. Passive or active filters are usually provided for a partial reduction of the line harmonics. A novel and superior approach employs a switched electronic compensator. It generates an exact replica of the harmonic current, feeding it to the high-voltage transformer to produce a harmonic counter MMF. The transformer main flux is then forced to be sinusoidal, and so is the induced voltage in the primary. The line current, being low-pass filtered by the transformer leakage inductance, assumes a pure sinusoidal waveform. The compensator operates in the low switching frequency range of the main power converters. Its installed power is only 1{%} of the traction power. Operation, control, and design considerations are described. Results from laboratory tests at full power level are presented. - 37.J. Holtz, "The dynamic representation of AC drive systems by complex signal flow graphs" in Proceedings of 1994 IEEE International Symposium on Industrial Electronics (ISIE'94), 1994, pp. 1--6.
Abstract:
Induction motors represent nonlinear higher-order dynamic systems of considerable complexity. They are well amenable to a formal mathematical analysis. It has proved more difficult, however, to comprehend and penetrate in an imaginative way the principles of their operation under transient conditions. Complex graphic signal flow graphs are suited to visualize the dynamic performance of AC machines. They can assist to form an understanding of the internal dynamic processes of a machine and their interactions with external controls.{\textless}{\textgreater} - 36.J. Holtz, W. Lotzkat and S. Stadtfeld, "Controlled AC drives with ride-through capability at power interruption", IEEE Transactions on Industry Applications, vol. 30, no. 5, pp. 1275--1283, 1994.
Abstract:
General purpose PWM inverter drives are equipped with an undervoltage protection mechanism, causing the system to shut down within a few milliseconds after a power interruption in the mains. This may entail loss or damage of material in such critical applications as the production of textile fibers, paper, or with extruder drives. The proposed solution to this problem is to recover some of the mechanical energy stored in the rotating masses. When a power interruption occurs, a sequence of fast feedforward commands is applied to force an immediate transition into the regeneration mode. During the interrupt interval, the drive system continues to operate at almost zero torque, just regenerating a minor amount of power to cover the electrical losses in the inverter. The method is implemented in an additional software package to be used with general-purpose inverter drives of limited dynamic performance. Experimental results are presented.{\textless}{\textgreater} - 35.J. Holtz and B. Beyer, "Fast current trajectory tracking control based on synchronous optimal pulsewidth modulation" in Proceedings of 1994 IEEE Industry Applications Society Annual Meeting, 1994, pp. 734-741 vol.1.
Abstract:
State-of-the-art pulsewidth modulation techniques fail to give satisfactory results when high-bandwidth torque control is required at the low switching frequency of modern high-power AC machine drives. A novel current control method refers to precalculated optimal synchronous pulse patterns. These are used to generate specific current reference trajectories to be adapted on line to the actual dynamic torque command. A fast tracking controller, operated in parallel to a conventional PI controller, minimizes the trajectory tracking error. The optimized current trajectories ensure fast response and minimum harmonic distortion.{\textless}{\textgreater}
