28.

A. Uphues, K. Nötzold, R. Griessel, R. Wegener and S. Soter, "Overview of LVRT-capability pre-evaluation with an inverter based test bench" in 2015 IEEE 24th International Symposium on Industrial Electronics (ISIE), 2015, pp. 748--753.

Abstract:
With increased renewable power penetration level the system operators of power grids require low-voltage ride-through (LVRT) capability of renewable power plants. The LVRT-capability has to be verified during the process of certification with precisely defined short circuit tests on a reactance based test bench. For the development of the fault ride through (FRT) capability the cost intensive reactance based test configuration is replaced by an inverter based voltage sag generator (VSG). This paper deals with an overview of the whole inverter based test configuration including the control structure of the grid emulator and the adjustment of the grid side converter's control structure to reach LVRT-capability as well as measurement results for the pre-evaluation.

27.

S. Gruber, R. Wegener and S. Soter, "Design Process for High Force Tubular Linear Drive with DiscreteWound Coils" in The 10th International Symposium on Linear Drives for Industry Applications, 2015.

26.

A. Uphues, K. Nötzold, R. Wegener and S. Soter, "Frequency adaptive PR-controller for compensation of current harmonics" in IECON 2014 - 40th Annual Conference of the IEEE Industrial Electronics Society, 2014, pp. 2103--2108.

Abstract:
The use of proportional resonant (PR) current controller in grid side wind power converters instead of the traditional proportional integral (PI) controller has gained a large popularity. Particularly its capability for compensating harmonics in the current waveforms is an essential feature. Due to the replacing of the generator side converter by a simple diode rectifier, harmonics with variable frequencies into dependence of the generator frequency appear in the current waveforms. To reach the IEEE standard for the total harmonic distortion (THD) a frequency adaptive PR-controller for compensating these harmonics is required.

25.

A. Uphues, K. Nötzold, R. Wegener, K. Fink, M. Bragard, R. Griessel and S. Soter, "Inverter based test setup for LVRT verification of a full-scale 2 MW wind power converter" in 2013 15th European Conference on Power Electronics and Applications (EPE), 2013, pp. 1--5.

Abstract:
With increased wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). This paper describes a full power test bench, designed to evaluate the functionality of grid connected converter in nominal operating mode and in case of LVRT. To verify the LVRT capability an inverter based voltage sag generator (VSG) is developed which emulates grid failures.

24.

A. Uphues, K. Nötzold, R. Wegener and S. Soter, "SOGI based grid fault detection for feeding asymmetrical reactive currents to fulfill LVRT requirements" in 2013 IEEE AFRICON, 2013, pp. 1--5.

Abstract:
Due to the increasing wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). Additionally the WT has to support the power system stability in LVRT cases by supporting the grid with reactive power. The amount of reactive power feed-in depends on the type of grid fault and the depth of the voltage dip. Therefore this paper shows a reliable grid voltage monitoring consisting on a second order generalized integrator (SOGI) structure. The resulting phase locked loop (PLL) is tolerant against grid faults and the amplitudes and phase angles of the individual phase voltages are detected.

23.

A. Uphues, K. Nötzold, R. Wegener, S. Soter and R. Griessel, "Support of grid voltages with asymmetrical reactive currents in case of grid errors" in 2013 IEEE International Conference on Industrial Technology (ICIT), 2013, pp. 1781--1786.

Abstract:
Due to the increasing wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). Additionally the WT has to support the power system stability in LVRT cases by supporting the grid with reactive power. By feeding symmetrical reactive currents in case of asymmetrical grid errors, as required in many actual grid codes, the phase voltage of the undistorted phase will increase above the upper voltage limit. This paper shows a strategy to feed asymmetrical reactive currents into the distorted grid without increasing the phase voltage in the undistorted phase.

22.

A. Uphues, K. Nötzold, R. Wegener, S. Soter and R. Griessel, "Inverter based voltage sag generator with PR-controller", 2012, pp. 1037--1042.

Abstract:
Due to the increasing wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). Additionally the WT has to support the power system stability in LVRT cases. To evaluate the LVRT capability of grid connected converter, a voltage sag generator (VSG) is required to emulate grid failures. This paper introduces a three phase programmable inverter based VSG, which is equipped with a cascaded control structure consisting of proportional resonant (PR) current controller and PR voltage controller. The described VSG is able to emulate all required voltage sags, propagated through a delta star connected transformer, very precisely. The control structure has been simulated and tested successfully on a 2MW full power testbench.

21.

S. Gruber, R. Wegener and S. Soter, "Detent force reduction of a tubular linear drive by using a genetic algorithm and FEM - verification of simulation results" in IECON 2012 - 38th Annual Conference of the IEEE Industrial Electronics Society, 2012, pp. 1731--1736.

Abstract:
In order to meet industrial safety standards in eccentric presses, the detent force caused by the reluctance change between permanent magnet (PM) and stator teeth of the acting high force tubular permanent magnet linear synchronous machines (PMLSM) should be reduced. The detent force is generated by two components: the slot effect which is already decreased by the closing slot technique and proven in [3] and the end effect which will be optimized by using auxiliary poles at the end of the machine. Therefore a special genetic algorithm (GA) is developed which rates the simulation results of the FEM and produces new auxiliary poles. The combined simulation tries to find an optimal size and position for auxiliary poles to reduce the whole detent force. The numerical calculations propose a minimized detent force caused by the located poles, which is independent from the length of the machines (1 to 5 modules). The result will be proven by measurements.

20.

A. Uphues, K. Nötzold, R. Wegener and S. Soter, "PR-controller in a 2MW grid side windpower converter" in 2012 IEEE International Conference on Industrial Technology, 2012, pp. 1073--1078.

Abstract:
To regulate the current in grid connected power converters mostly proportional integral (PI) controller in synchronous reference frame are used. To improve their known drawbacks such as complexity of control structure because of the dq-transformation and the poor behavior concerning low order harmonics compensation, proportional resonant (PR) controller gained a large popularity. This paper describes the differences between using PI-controller and PR-controller in a 2MW grid connected power converter for wind turbines. The control theory of PR filters and implementing them as delta based infinite impulse response (IIR) filters in a fixed-point microcontroller is presented. The PR-controller with harmonic compensation has been tested in a 2MW power converter.

19.

R. Wegener, K. Nötzold, A. Uphues, R. Griessel and S. Soter, "Test bench for multi-MW grid side wind power converter" in 2011 IEEE AFRICON, 2011, pp. 1--5.

Abstract:
This paper deals with an integrated full power test bench for the grid side of a wind power converter. The speciality is the high side voltage and current measurement to use the stray inductance as an additional filter element. The presented test bench is enhanced for fault ride through measurement capabilities with a full power grid simulator.