Veröffentlichungen
- 174.T. Boller, J. Holtz and A. K. Rathore, "Neutral-Point Potential Balancing Using Synchronous Optimal Pulsewidth Modulation of Multilevel Inverters in Medium-Voltage High-Power AC Drives", IEEE Transactions on Industry Applications, vol. 50, no. 1, pp. 549--557, 2014.
Abstract:
This paper presents neutral-point potential (NPP) balancing while maintaining low harmonic distortion using optimal pulsewidth modulation (PWM) of a multilevel inverter for medium-voltage high-power industrial ac drives. This method is applicable for five-level inverters or higher. A high performance of the machine is observed experimentally at low-switching-frequency operation employing the proposed technique. In the past, low distortion and optimal common-mode voltage at low-switching-frequency control have been reported using proposed synchronous optimal PWM. - 173.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.
ISBN: 2153-0033
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. - 172.A. Bartsch, F. Senicar, S. Kratz and S. Soter, "Enhanced FPGA based three level space vector pulse width modulation with active neutral point balancing" in 2013 IEEE Energy Conversion Congress and Exposition, 2013, pp. 1748--1753.
ISBN: 2329-3748
Abstract:
This paper presents an FPGA based implementation of an improved space vector pulse width modulation for neutral point clamped three-level topologies. For this purpose the flatspace modulation calculating the timings is used in combination with an optimized switching pattern to reduce the switching edges to a minimum. Additionally a combination of two methods for balancing the neutral point is developed which are both implemented without adding any additional harmonics to the modulated output. - 171.B. Krüger, S. Gruber and S. Soter, "Controlling of medium voltage power-factor of photovoltaic power plants from the low voltage side" in 2013 IEEE Energy Conversion Congress and Exposition, 2013, pp. 569--574.
ISBN: 2329-3748
Abstract:
The effort to make the production of electrical energy much more environmental-friendly, large conventional power plants will be replaced by several smaller regenerative power plants. In order to improve stability and controllability, these smaller power plants are supposed to control the active power, the reactive power and the power factor in the medium voltage grid like conventional power plants. This paper will discuss three different methods to control the medium-voltage power factor from the low voltage side in consideration of parasitic effects from cables and transformers to fulfill the guidelines at the grid connection point. A method with a self-learning-algorithm will be implemented and proven by simulations and measurements on a test bench with inverter and 400 V to 10 kV grid transformer. The self-learning-algorithm will give the opportunity to reach every required power factor at the grid connection point. - 170.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. - 169.J. Holtz and X. Qi, "Optimal Control of Medium-Voltage Drives---An Overview", IEEE Transactions on Industrial Electronics, vol. 60, no. 12, pp. 5472--5481, 2013.
Abstract:
Carrier modulation is the most common method for inverter control of ac drive systems. Operation at switching frequencies of several kilohertz is customary to restrain the harmonic distortion of the motor currents. Lower switching frequency is preferred for medium-voltage drives, owing to the higher switching losses of the semiconductor devices. This calls for optimizing the performance of the pulsewidth modulator. Improvements are achieved by abolishing carrier modulation with its equidistant time spacing of the voltage pulses. Optimal pulse patterns can be precalculated for every steady-state operating point of the drive. The patterns are stored in a memory of the drive system, from which they are retrieved and used for inverter control. Control at transient operation is achieved by adapting the optimal steady-state pulse patterns to the respective situation. Specific trajectories of the motor current space vector are then created by online optimization. An alternative method of online optimization relies on predicting the space vector trajectories for the next possible inverter switching states. The switching state that leads to minimum switching frequency is then selected. Optimal pulsewidth modulation reduces harmonic distortion. It permits operation at very low switching frequency and reduces the switching losses. This increases the current-carrying capability of the semiconductor devices to the extent that the power rating of an inverter approximately doubles. - 168.F. Senicar, A. Bartsch, K. Klitzke and S. Soter, "Improved high bandwidth current controller for FPGA based inverter drives" in 2013 IEEE AFRICON, 2013, pp. 1--6.
ISBN: 2153-0033
Abstract:
This paper presents the improvement of the precision and bandwidth of the current control loop implemented in a field programmable gate array (FPGA) based inverter. By compensating the nonlinear effects of the IGBT power stage with a feed forward control, the current controller is relieved resulting in an output current with less harmonics and a better frequency response. In order to improve the current control loop even further, a current observer, based on a Luenberger observer is implemented. - 167.S. Gruber, B. Krüger and S. Soter, "High force tubular linear actuator with integrated eddy current brake for spring-loaded systems" in 2013 IEEE AFRICON, 2013, pp. 1--5.
ISBN: 2153-0033
Abstract:
In order to meet safety standards in manufacturing industry many production machines are equipped with safety stop functions based on spring-loaded systems. This paper deals with an integrated eddy current brake of a high force tubular permanent magnet linear actuator for hydraulic applications with small actuating pathes. An analytical description of different design criteria for the integrated eddy current brake are shown. The special not rotational symmetrical design of the tubular linear actuator is transferred to a 2D transient FEM simulation model to predict the braking behavior caused by the spring load in case of an emergency stop. Measurements on a test bench are in good agreement with the simulation results and are used to validate the model. - 166.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. - 165.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.
