Veröffentlichungen
- 50.L. Springob and J. Holtz, "High-bandwidth current control for torque-ripple compensation in PM synchronous machines", IEEE Transactions on Industrial Electronics, vol. 45, no. 5, pp. 713--721, 1998.
Abstract:
Active compensation of torque harmonics in high-performance synchronous permanent magnet (PM) motor drives requires high-bandwidth current control. It is demonstrated that proportional integral (PI) current control exhibits performance limits, even when feedforward compensation of the rotor induced voltage and the stator inductance drop is used. High bandwidth requirements are satisfied using a digital deadbeat current controller. Sampling time delays are eliminated to the extent possible by means of a current predictor. The current controller and the predictor refer to a model of the parasitic effects of the PM synchronous machine that is acquired and adapted to parameter changes in real time. Stator current distortions due to deviations from the sinusoidal flux linkage distribution are thus eliminated. The control system facilitates compensation of high-frequency torque ripple of the machine. - 49.A. M. Khambadkone and J. Holtz, "Fast current control for low harmonic distortion at low switching frequency", IEEE Transactions on Industrial Electronics, vol. 45, no. 5, pp. 745--751, 1998.
Abstract:
The structure of the current control loop of an induction machine drive determines decisively the dynamic performance of the overall system. Fast current control is a prerequisite for dynamic decoupling between the torque and the flux commands. Standard solutions are well established for drives in the low- and medium-power ranges. The low switching frequency of high-power pulsewidth modulation inverters calls for a tradeoff in controller design between the low harmonic losses and torque ripple in the steady state on one hand, and fast dynamic response during the transients on the other. The problem is developed in detail. A variable-structure approach is proposed as the solution. - 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.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. - 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.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. - 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}
