27.

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.

26.

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

25.

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

24.

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.

23.

R. Wegener, S. Soter and C. Deipenbrock, "Sensorless Determination of the Exact Rotor Position of a Blocked Permanent Magnet Machine" in PCIM Asia 2006, 2006.

22.

R. Lach and S. Soter, "Measuring method for determining the reasons of magnetically caused structure-borne sound on electrical drive systems" in 2005 European Conference on Power Electronics and Applications, 2005, pp. 10 pp--P.10.

Abstract:
A special signal processing method (order analysis) allows well-defined conclusions from accelerometer measurements on electrical drives regarding the reasons of structure-borne and airborne sound. In this paper an analysis of acceleration signals of an 5 kW induction machine is presented. The special feature is that a projection of sound curves is included in this analysis. Thus it is possible to assign an oscillation excitation to harmonics attributed to the machine design or harmonics of the feeding frequency converter.

21.

S. Soter, R. Wegener, J. Dopheide and B. Kiffer, "Low cost vector control for permanent-magnet-synchronmotor with only one DC-link current sensor for pumping application" in IEEE International Conference on Electric Machines and Drives, 2005, 2005, pp. 174--177.

Abstract:
This paper presents a cost-efficient closed loop control of a small permanent magnet machine for pumping application. The special feature of the described solution is only one current probe in the DC-link of the converter. The three phase currents are calculated from this measured current in combination with the state of semiconductors at the time of measurement. Near the sector borders of the space vector modulation the turn-on-time of one semiconductor is too short for measuring the current. A method is developed to compensate these blind areas with the extension of the turn-on-time in half of the PWM-cycles. The measured values are checked by an error detection and exchanged if necessary by an approximation. The position of the rotor is also calculated from the measured current. The paper presents a close loop vector control with less costs than conventional solutions.

20.

F. Bertling and S. Soter, "Increasing efficiency of an DSP-controlled converter by on-the-fly changing of the gate drive method" in 2005 IEEE 6th International Conference on Power Electronics and Drive Systems (PEDS), 2005, pp. 448--451.

Abstract:
This paper demonstrates how bypassing the MOSFETs body diodes in a full bridge application by freewheeling of the transformer current through the MOSFETs of one input leg decreases the power losses, depending on the operating point. A gate drive control via a modern digital signal processor is described that allows an on-the-fly change of the gate drive method so that freewheeling is activated or deactivated as required to obtain lowest losses in a wide operating range. Unlike other approaches to bypass the MOSFETs body diodes, this technique requires no additional circuit parts (e.g. external freewheeling diodes). The effect of freewheeling on power losses is illustrated by measurements of the current and voltages run, MOSFET temperatures and the characteristic curve of power losses

19.

F. Bertling and S. Soter, "Improving grid voltage quality by decentral injection of current harmonics" in IECON 2005 - 31th Annual Conference of the IEEE Industrial Electronics Society, 2005, pp. 3 pp.

Abstract:
This research project deals with the development of an adjustable converter for injection of fuel cell power. A DC/DC converter stage increasing the voltage level is connected to a DC/AC inverter for grid current injection via a high capacitance DC link. This decouples the momentary power drawn from the energy source from the momentary power being injected into the grid, allowing arbitrary output current waveforms without an increase of input current ripple. Conventionally, pure fundamental frequency currents are considered the optimum waveform regarding the injected currents impact on the grid. This paper demonstrates how grid voltage harmonics caused by nonlinear loads can be minimized by adapting the converters injected current shape. In contrast to harmonics compensation in industrial applications where the compensation current is determined by measuring the local loads current harmonics, the intended decentral application in private houses suggests a different approach to improve overall grid voltage quality. The digital signal processor used for the converters control and monitoring functions calculates the frequency spectrum of the measured grid voltage run by digital Fourier transformation (DFT) and determines the current harmonics necessary to counteract the present voltage harmonics. The resulting current frequency spectrum is modulated into a time dependant current shape that is added to the fundamental frequency current run determined by the requested amounts of active and reactive power. This way, harmonic currents of the local loads are compensated without changes in the house installation for measuring the loads currents. Also current harmonics of neighbouring houses are compensated.

18.

A. Wirsen and S. Soter, "Berührungslose Drehmomenterfassung - Turbosätze altern unter strengeer Beobachtung", SENSOR report, vol. 2004, no. 4, 2004.