112.

S. Soter and R. Wegener, "Development of Induction Machines in Wind Power Technology" in 2007 IEEE International Electric Machines & Drives Conference, 2007, pp. 1490--1495.

Abstract:
This paper gives an overview of the development of the induction machine as a generator for wind turbines from the middle of the 20th century up to now. After a short history chapter the different energy conversion concepts are presented. At first a squirrel cage machine is direct coupled to the grid (Danish concept). To adjust the machine speed the second step is a wound rotor machine with collector rings to change rotor resistance. This concept allows the first adaption of the operating point of the wind turbine and the induction machine. Another concept is to connect the stator of a squirrel cage machine with a full inline voltage source converter to the grid to get the flexibility in rotational speed and to control the reactive power. The doubly fed induction machine is the latest development. This concept uses a bidirectional voltage source converter in the rotor circuit with a rated power of only 30{%} of the rated generator power. Now it is possible to change the rotational speed and the reactive power independently and in a wide range. A generalized control scheme of a modern doubly fed induction machine (DFIG) is shown in the last part to explain the variability and the range of application. Today over 70{%} of the wind turbines are build up with DFIG.

111.

R. Wegener, F. Senicar, C. Junge and S. Soter, "Low Cost Position Sensor for Permanent Magnet Linear Drive" in 2007 IEEE 2nd International Conference on Power Electronics and Drive Systems (PEDS), 2007, pp. 1367--1371.

Abstract:
This paper deals with a custom made low cost sensor for measuring the position of a permanent magnet linear motor. The principle how to measure position and movement direction with two analog hall sensor elements is described. The following simulated and detailed error and failure treatment is very important to know exactly the performance and the possibilities of this low cost sensor element. Afterwards this position sensor is build and some measurements with a linear machine is done. After filtering, the accuracy of the two signals is high enough to be an input of a converter control to determine the correct current which has to be injected. If there is another higher ranking closed-loop control, e.g. pressure, flow or force, in the control system this low cost sensor is sufficient and works very well. It is possible to implement the very small sensor in the housing of the linear drive. This sensor costs less than 15 dollar and can not be compared to a very precise working linear senor for some hundred dollar in order to position the linear drive very exact but the accuracy is high enough to build a lower ranking closed-loop control and to stabilize a complex control system of converter, linear drive and load.

110.

H. Abu-Rub, H. Schmirgel and J. Holtz, "Maximum Torque Production in Rotor Field Oriented Control of an Induction Motor at Field Weakening" in 2007 IEEE International Symposium on Industrial Electronics, 2007, pp. 1159--1164.

Abstract:
This paper presents a highly dynamic rotor flux- oriented control system of an induction motor in the field weakening region. The control system guarantees maximum torque production taking into account voltage and current limits. The approach permits operation without using a speed sensor. The system is investigated by simulation in real time and experimentally using a fixed point microcontroller.

109.

F. Bertling and S. Soter, "Real-time prediction of the steady state temperature of circuit components as a tool for power electronic circuit testing" in PCIM Europe, 2007.

108.

H. Abu-Rub and J. Holtz, "Rotor Oriented Nonlinear Controlsystem of Induction Motors Operatingat Field Weakening" in IECON 2007 - 33rd Annual Conference of the IEEE Industrial Electronics Society, 2007, pp. 1085--1090.

Abstract:
In the presented paper, the above mentioned system is used as a solution for maximum steady-state torque production at field weakening. Forming of temporary voltage for fast reaction to dynamic changes is taken into account. The method is applied to nonlinear rotor oriented control system using nonlinear feedback. Such system insures full decoupling between mechanical and electrical variables which is very advantageous particularly at field weakening region. Real time simulation results are curried out.

107.

J. Holtz, "Guest Editorial", IEEE Transactions on Industrial Electronics, vol. 53, no. 2, pp. 350--351, 2006.

106.

J. Holtz, "Sensorless Control of Induction Machines---With or Without Signal Injection?", IEEE Transactions on Industrial Electronics, vol. 53, no. 1, pp. 7--30, 2006.

Abstract:
Controlled induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information on the rotor speed is extracted from measured stator currents and from voltages at motor terminals. Vector-controlled drives require estimating the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. Dynamic performance and steady-state speed accuracy around zero speed range are achieved by signal injection, exploiting the anisotropic properties of the machine. The overview in this paper uses signal flow graphs of complex space vector quantities to provide an insightful description of the systems used in sensorless control of induction motors.

105.

F. Bertling and S. Soter, "A novel converter integrable impedance measuring method for islanding detection in grids with widespread use of decentral generation" in International Symposium on Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006, 2006, pp. 503--507.

Abstract:
This paper proposes a method for measuring the impedance of the public grid for islanding detection by grid connected converters performing decentral power injection. Based on subharmonic (noncharacteristic to the grids fundamental frequency) test current injection and grid voltage frequency component detection to give a defined value for the frequency dependent impedance, a modulation of the subharmonic test currents amplitude with a pulse pattern assigns each converter an individually detectable {\textquotedbl}signature{\textquotedbl} for its test signal. This allows a larger number of converters to be operated within a grid segment without interference of their measurements causing unintended grid disconnections

104.

R. Wegener, S. Soter and T. Rösmann, "Facility Employing Standard Converters for Testing DFIG Wind Generators up to 30kW" in 2006 IEEE 15th International Symposium on Industrial Electronics (ISIE), 2006, pp. 1025--1029.

Abstract:
This paper presents a test facility for a double fed induction generator (DFIG) with a rated power of approximately 30 kW. The stator of the machine is directly connected to the grid and the rotor is fed with variable voltage and frequency. Actually such machines are used in wind generators with a power of more than 500 kW with special built converters. In the presented test facility the used converter consists of two standard low cost voltage source converter units with connected DC-link. The firmware of these converters are normally not suitable for feeding the rotor because there are not able to calculate the slip frequency and phase in real time. In the presented solution this is programmed in two application modules plugged into the converter. The equivalent network parameters of the DFIG are determined by the converter. These are necessary for the development of an analytical model of the system to set up a closed loop active and reactive power control. The test system provides the ability to control both power types decoupled and with a linear characteristic

103.

R. Wegener, S. Soter and T. Rösmann, "Operation of double fed induction generators with unmodified low cost standard converters" in 2006 37th IEEE Power Electronics Specialists Conference, 2006, pp. 1--5.

Abstract:
This paper presents how to operate a double fed induction generator (DFIG) with a rated power of approximately 30kW with unmodified low cost standard converters. The stator of the machine is directly connected to the grid and the rotor is fed with variable voltage and frequency from two standard low cost voltage source converters. Actually such machines are used in wind generators with a rated power of more than 500 kW with special build converters. In the presented solution the rotor of the DFIG is fed with two DC-Link connected standard voltage source converters. The original software is designed to calculate speed and phase of the rotor by receiving a speed signal from the rotor shaft. Therefore it is necessary to add two small application modules to modify the firmware externally to realize the calculation of slip frequency and phase in real time. The equivalent network parameters of the DFIG are determined by the converter itself by using an autotune function. With this parameters it is possible to develop an analytical model of the system to set up a closed loop active and reactive power control. The test system provides the ability to control both power types decoupled and with an approximately linear characteristic.