Veröffentlichungen
- 30.Y. Lou and J. Holtz, "Improving the performance of industrial robot manipulators by neural networks" in Proceedings of IECON'94 - 20th Annual Conference of IEEE Industrial Electronics, 1994, pp. 1265-1270 vol.2.
Abstract:
Robot manipulators are nonlinear systems. Centrifugal and Coriolis forces as well as the influence of gravitation and friction depend on the state variables of the system. In the presence of strong nonlinearities, linear PID controllers for the individual joint axis drives, usually employed in industrial applications, cannot provide satisfactory performance due to their inherent limitations. Model-based schemes have the disadvantage that they require accurate system models, which are difficult to obtain. The problem is solved by using multilayer feedforward neural networks, which do not rely on a system model. They are used as an addition to the existing linear individual joint control structure. The convergence of the system is proved using Lyapunov's stability theory. Experiments obtained on a two-degree-of-freedom manipulator demonstrate the effectiveness of the proposed technique.{\textless}{\textgreater} - 29.S. Soter, "Systemtechnik für photovoltaisch gespeiste Asynchronmaschinen zum Antrieb von Wasserpumpen" in Programm zur Einführung photovoltaischer Pumpen, GTZ, Eds. 1994.
- 28.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} - 27.J. Holtz, "The induction motor-a dynamic system" in Proceedings of IECON'94 - 20th Annual Conference of IEEE Industrial Electronics, 1994, pp. P1-P6 vol.1.
Abstract:
Induction motors are 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} - 26.J. Holtz, M. Stamm and O. Stielau, "The performance of high-power GTOs operated as fast turn-off thyristors" in Proceedings of IECON'94 - 20th Annual Conference of IEEE Industrial Electronics, 1994, pp. 112-117 vol.1.
Abstract:
The series resonant DC link inverter is an attractive circuit topology for interfacing a superconducting magnetic energy storage (SMES) inductance with the electric utility. The principle of zero current switching (ZCS) ensures low switching losses at high switching frequency, provides power factor correction capability, and reduces the harmonic line currents. For applications at high power level, the use of GTOs as semiconductor switches is mandatory. High-power devices behave differently at switching than the smaller GTOs treated in previous publications. The device losses in the kiloampere range are reduced by gate-assisted forward recovery. The dynamic performance of different power switch topologies is experimentally evaluated.{\textless}{\textgreater} - 25.J. Holtz and B. Beyer, "Optimal synchronous pulsewidth modulation with a trajectory-tracking scheme for high-dynamic performance", IEEE Transactions on Industry Applications, vol. 29, no. 6, pp. 1098--1105, 1993.
Abstract:
Synchronous pulse-width modulation (PWM) based on precalculated and stored optimal pulse patterns could be a superior method for the control of high-power inverters operated at low switching frequency. The technique has rarely been applied in practice owing to its poor dynamic performance. A novel feedforward control technique eliminates this decisive drawback: the space vector of the machine currents is forced to track a precalculated optimal trajectory in the steady-state and under the transient operating conditions commanded by the drive control system. Undesired transients caused by the pulse-width modulator are avoided. Experimental results obtained from a 30 kW AC drive are presented.{\textless}{\textgreater} - 24.J. Holtz and L. Springob, "Reduced harmonics PWM controlled line-side converter for electric drives", IEEE Transactions on Industry Applications, vol. 29, no. 4, pp. 814--819, 1993.
Abstract:
The concept for a reduced-harmonics PWM modulator, as applied for the control of a line-side power converter for a variable speed AC motor drive, is described. The PWM algorithm determines the on-state duration of each switching vector based on the observation of the time-variable voltage reference vector. Since there is no reference made to a constant-frequency carrier signal, the generated pulse patterns become asynchronous. It is the essential property of this method to produce a quasicontinuous harmonic spectrum in which all frequency components have more or less equal magnitudes. This is an advantage as compared with carrier-based PWM control schemes that exhibit high-amplitude carrier and side-band components in their harmonic spectra. The emission of acoustic noise radiated from the AC filter inductor is reduced.{\textless}{\textgreater} - 23.J. Holtz, "Speed estimation and sensorless control of AC drives" in Proceedings of IECON '93 - 19th Annual Conference of IEEE Industrial Electronics, 1993, pp. 649-654 vol.2.
Abstract:
The operation of speed controlled AC 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 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 description of the physical and mathematical systems used in sensorless control.{\textless}{\textgreater} - 22.J. Holtz and J. O. Krah, "Adaptive optimal pulse-width modulation for the line-side converter of electric locomotives", IEEE Transactions on Power Electronics, vol. 7, no. 1, pp. 205--211, 1992.
Abstract:
Two methods of generating synchronous online optimal PWM sequences for the line-side converter of electrical locomotives are described. The properties of the feeding supply line render the system oscillatory at multiple resonance frequencies, which are time-variable functions of the railway track topography and of the respective locations of traction vehicles. The prevailing topographic conditions define a time-variable virtual model of the overhead line, the harmonic energy of which is the optimum criterion to be minimized. The 176 switching instants of a nine-level PWM converter voltage are optimized using an online algorithm. The necessary computations are performed in the time intervals between two commutations. The performance is illustrated by measurements obtained from a real-time multiprocessing model of an extended railway track topography, including substations and locomotives. The developed hardware structure is designed for the implementation in a railway traction vehicle.{\textless}{\textgreater} - 21.A. M. Khambadkone and J. Holtz, "Low switching frequency and high dynamic pulsewidth modulation based on field-orientation for high-power inverter drive", IEEE Transactions on Power Electronics, vol. 7, no. 4, pp. 627--632, 1992.
Abstract:
In megawatt-rated inverter-fed induction motor drive systems, the gate-turn-off switching losses account for a considerable amount of the total losses, hence, the switching frequency in such systems must be kept at a low value of only a few hundred hertz. To avoid undesired torque harmonics under such operating conditions, the pulse control of the inverter is made dependent on the orientation of the rotor flux of the drive machine. This method transfers a major portion of the unavoidable current distortions into the field axis where they have no influence on the machine torque. An optimal trajectory-oriented control is presented that achieves low switching frequency at low torque and current harmonics and exhibits a very fast dynamic response. The performance of this method is demonstrated by measured results from a 30-kW model drive.{\textless}{\textgreater}
