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}

20.

J. Holtz, "Pulsewidth modulation-a survey", IEEE Transactions on Industrial Electronics, vol. 39, no. 5, pp. 410--420, 1992.

Abstract:
The author evaluates the state of the art in pulsewidth modulation for AC drives fed from three-phase voltage source inverters. Feedforward and feedback pulsewidth modulation schemes with relevance for industrial application are described and their respective merits and shortcomings are explained. Secondary effects such as the influence of load-current dependent switching time delay and transients in synchronized pulsewidth modulation schemes are discussed, and adequate compensation methods are presented. Recorded oscillograms illustrate the performance of the respective pulsewidth modulation principles. The author provides a guideline and quick reference for the practicing engineer to decide which methods should be considered for an application of a given power level, switching frequency, and dynamic response.{\textless}{\textgreater}

19.

J. Holtz and J. O. Krah, "Suppression of time-varying resonances in the power supply line of AC locomotives by inverter control", IEEE Transactions on Industrial Electronics, vol. 39, no. 3, pp. 223--229, 1992.

Abstract:
The harmonic currents generated by the line-side converter of an electric locomotive are injected into the overhead supply system. Although low in magnitude, they give rise to traveling waves that start propagating in both directions along the overhead line. The traveling waves are reflected at various electrical discontinuities along the line such as the feeding substations and other traction vehicles, the positions of which are time varying. This produces eigenresonances at multiple frequencies. High resonant currents may be generated that cause problems of electromagnetic interference with railway communication and signaling systems. It is demonstrated that the time-varying eigenresonances can be identified in real time. Methods of optimal adaptive inverter control are employed in order to avoid the excitation of the line resonances.{\textless}{\textgreater}

18.

J. Holtz, W. Lotzkat and A. M. Khambadkone, "On continuous control of PWM inverters in the overmodulation range including the six-step mode" in Proceedings of the 1992 International Conference on Industrial Electronics, Control, Instrumentation, and Automation, 1992, pp. 307-312 vol.1.

Abstract:
The power output and the dynamic performance of pulse width modulation (PWM)-controlled AC motor drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to the maximum possible value, which is reached in the six-step mode. The solutions differ in their approach. A space vector strategy is used for high dynamics performance high switching frequency drives, while a field-oriented PWM method is used for low switching frequency high power inverters. The methods are described and analyzed, and experimental results are presented.{\textless}{\textgreater}

17.

J. Holtz and B. Beyer, "Optimal synchronous pulsewidth modulation with a trajectory tracking scheme for high dynamic performance (invertor control)" in [Proceedings] APEC '92 Seventh Annual Applied Power Electronics Conference and Exposition, 1992, pp. 147--154.

Abstract:
It is noted that synchronous pulsewidth modulation 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 feedforward control technique eliminates this 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 pulsewidth modulator are avoided. Experimental results obtained from a 30 kW AC drive are presented.{\textless}{\textgreater}

16.

J. Holtz, "Pulsewidth Modulation in Motion Control" in Singapore International Conference on Intelligent Control and Instrumentation [Proceedings 1992], 1992, pp. 115--120.

Abstract:
University of Wuppertal, Germany

15.

J. Holtz and E. Bube, "Field-oriented asynchronous pulse-width modulation for high-performance AC machine drives operating at low switching frequency", IEEE Transactions on Industry Applications, vol. 27, no. 3, pp. 574--581, 1991.

Abstract:
A novel pulse-width modulation (PWM) technique is based on the prediction of the trajectory patterns that the stator current vector describes in a field-oriented coordinate system. The method of field-oriented PWM control minimizes the switching frequency at given torque ripple. The harmonics of the field producing current are left to develop freely, permitting operation at values of switching frequency that are lower than those of the optimal schemes known so far. The optimal switching times are computed off line and are called from a memory during operation. Signal processing is performed in a simple hardware structure.{\textless}{\textgreater}

14.

D. Antic and J. Holtz, "High-efficiency dual transistor base drive circuit based on the Cuk converter topology", IEEE Transactions on Industrial Electronics, vol. 38, no. 3, pp. 161--165, 1991.

Abstract:
A dual transistor base drive circuit that unifies all important functions (on-state base current power supply for two power transistors, off-state negative U/sub be/ =-5 V base-emitter voltage, overcurrent and short-circuit protection scheme based on saturation voltage, and on- and off-state monitoring circuits) is described. The unit provides two base drive outputs using a single switching converter. It can be used to control two individual power transistors in different inverter configurations, e.g. common emitter or bridge configuration. The concept of a dual transistor base drive circuit using the Cuk switching regulator topology enables the low volume construction of a high-efficiency base drive unit for a high-power transistor inverter bridge leg. The circuit is powered from a common DC rail. The base current waveforms are characterized by steep slopes and an overcurrent peak at turn on.{\textless}{\textgreater}

13.

J. Holtz and T. Thimm, "Identification of the machine parameters in a vector-controlled induction motor drive", IEEE Transactions on Industry Applications, vol. 27, no. 6, pp. 1111--1118, 1991.

Abstract:
High dynamic performance of pulse-width-modulated (PWM) inverter-fed induction motor drives was achieved by using the method of field-oriented control. This method requires the actual value of the rotor time constant as essential system information, based on how the magnitude and the position of the rotor flux are calculated. An online identification technique for the rotor time constant and for other machine parameters is described. The identification is based on an evaluation of the stator current trajectory, which is the dynamic response of the induction motor to the PWM-switching sequence. An analytical machine model is operated in parallel to the actual machine, having the stator voltages and the mechanical speed of the induction motor as input signals. The coincidence of the two stator current trajectories of the model and the machine serves as an error indicator for the parameter identification scheme, permitting repetitive updates of the model parameters.{\textless}{\textgreater}