Veröffentlichungen
- 199.X. Qi and J. Holtz, "The Relationship Between Root Locus and Transient Field Components of AC Machines", IEEE Transactions on Industrial Electronics, vol. 67, no. 3, pp. 1836--1843, 2020.
Abstract:
The dynamic analysis of induction motors is supported by well-known theories: the two-axes transformation, and the space vector theory. Yet some inconsistencies with the theory of dynamic systems exist. The machine eigenvalues suggest the existence of two damped oscillators, physically not understandable. The respective eigenfrequencies change with the angular velocity of the reference frame. This contradicts the understanding that eigenfrequencies are inherent system properties. Physically, the dynamics depend on the continuous distribution of magnetic energy and its spatial displacement during transient processes. Information on the system dynamics is lost when dividing the continuum of magnetic energy into discrete portions. Complex state variables associate the dynamics to the propagation in space of distributed magnetic fields. The dynamic analysis reveals the existence single-complex eigenvalues. These define a novel class of system identifiers. They are characterized by having only one imaginary part instead of a conjugate complex pair. The use of complex state variables conveys insight and physical understanding of the dynamic processes within the machine. The approach constitutes an extension to the theory of dynamic systems. - 198.D. Maune, B. Krüger, P. Sahm and S. Soter, "Speed Control for Lifting Devices with Conical Cable Drum through Indirect Position Determination" in 2020 IEEE International Conference on Industrial Technology (ICIT), 2020, pp. 401--405.
ISBN: 2643-2978
Abstract:
Lifting devices are often provided with a spring to compensate their constant weights. But because the force of a spring is depending on its stretch, the compensation ratio during a lifting process is fluctuating. By changing the characteristic of the load with the help of a variable radius drum it is possible to mitigate this drawback. In this paper a torsion spring and a conical cable drum are used for compensation. Because the wound cable length per revolution is changing, the lifting speed also varies. For the introduced speed controller the position of the drum is measured with an absolute, magnetic sensor. The actual lifting speed is then indirectly determined by calculation utilizing the cable drum parameters. - 197.T. Schneider, S. Kratz, R. Wegener and S. Soter, "Symmetrical Bidirectional CLLC-Converter with Simplified Synchronous Rectification for EV-Charging in Isolated DC Power Grids" in 2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019, pp. 990--995.
ISBN: 2163-5145
Abstract:
This paper presents a bidirectional CLLC resonant converter for the use in electric vehicle fast charging applications, fed from a trolley bus DC power grid. Bidirectional converters generally introduce an increase in design complexity as well as a decreased power density and conversion efficiency, compared to their unidirectional equivalents. The presented converter, because of its symmetrical layout, is able to concentrate all necessary resonant inductances in one passive component and uses a simplified sensorless synchronous rectification technique in order to mitigate these drawbacks. A 12.5kW CLLC prototype for input voltages between 600-800V and output voltages between 300-400V is used for validation. The achieved maximum efficiency equals 96.6{%}. - 196.B. Krüger, S. Kratz, T. Theopold and S. Soter, "Wear Reduction Control Method in a Blade Pitch System of Wind Turbines" in 2019 IEEE 28th International Symposium on Industrial Electronics (ISIE), 2019, pp. 1107--1112.
ISBN: 2163-5145
Abstract:
Mechanical transformation of speed is needed in a lot of industrial applications but it is attended by backlash. Gear parts without closed linkage can accelerate and crash to another. So with the backlash comes the wear. There are many technical solutions and ideas to reduce the backlash by mechanical and electrical components and adaptions, but in most cases with the goal to increase the precision. In some applications, like the described pitch drive, the precision is not the problem and the increasing costs for backlash elimination are not to justified because the reduction of wear is more important. Further the extensive adaption has influence on functional safety and maintenance. This paper gives a short overview of mechanisms that reduce the wear in a given application without mechanical adaptions, only by adding a software module. In the first step backlash is detected and in dependence on its reason in a second step a reaction is induced by the drive to spare the mechanics. - 195.J. O. Krah, J. Holtz and B. Sahan, "Control of a Hybrid IGBT-SiC Inverter" in 2019 2nd International Conference on Smart Grid and Renewable Energy (SGRE), 2019, pp. 1--6.
Abstract:
A novel inverter topology built from a combination of 1.2 kV (standard) IGBTs and SiC-MOSFETs has an attraction for power applications. It consists of twelve controllable semiconductor devices per phase, contained in two identical modules. The complexity of this arrangement requires a coordinated commutation which is the subject of this paper. Concatenated state machines are used for this purpose. Extremely low harmonic content of the output voltage is obtained by interleaved pulsewidth control of two three-level inverter modules per phase. The IGBTs operate uniquely in a soft commutation mode which leads to unprecedented efficiency. - 194.J. O. Krah, T. Schmidt and J. Holtz, "Predictive Current Control with Synchronous Optimal Pulse Patterns" in 2019 2nd International Conference on Smart Grid and Renewable Energy (SGRE), 2019, pp. 1--6.
Abstract:
A method is described that generates synchronous optimal pulse patterns for inverter control in real time. A smart technique, which predicts the current trajectory, closes the current loop with implicit generation of optimized pulse patterns while eliminating all subharmonic components. The algorithm requires very little computational effort, which makes it applicable for low power systems operating at high switching frequency. - 193.S. Kratz, A. Schmidt, B. Krüger, R. Wegener and S. Soter, "Power Supply of a Short-Range Public Transportation System Based on Photovoltaics - Potential Analysis and Implementation" in 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC), 2019, pp. 3077--3081.
ISBN: 0160-8371
Abstract:
This paper answers the question of if an existing short-range public transportation system in a German town called Solingen could be exclusively supplied by photovoltaics and presents a fitted device for energy conversion. Based on the results of the proposed method for a photovoltaic potential analysis, the above question is answered and the main benefits of the direct integration of photovoltaic arrays are shown. The presented measurements of a 10kW prototype show that a high conversion efficiency can be achieved. - 192.S. Kratz, P. Hanses, B. Krüger, R. Wegener and S. Soter, "Integration of Second Life Batteries into a Smart Overhead Contact System based on SiC-Technology" in 2019 IEEE Transportation Electrification Conference and Expo (ITEC), 2019, pp. 1--5.
ISBN: 2377-5483
Abstract:
This paper presents the starting situation and some interim results of a research project with the aim of a fully electrified short-range public transportation in a German town called Solingen. It gives an insight to the existing trolleybus infrastructure and the benefits of second life battery usage. Following, the design configuration of a refurbished trolleybus battery system for stationary usage in substations is shown and evaluated. Based on this a new silicone carbide power electronic for a direct integration of stationary battery systems are proposed and evaluated. Available semiconductors for the prototype are specified and compared by measurements. The results show that the integration of trolleybus batteries can be done with high system efficiency. - 191.S. Kratz, B. Krüger, R. Wegener and S. Soter, "Integration of Photovoltaics into a Smart Trolley System Based on SiC-Technology" in 2018 IEEE 7th International Conference on Power and Energy (PECon), 2018, pp. 168--173.
Abstract:
This paper gives an insight to a research project with the aim of a fully electrified short-range public transportation in a German town called Solingen. It starts with an overview of the special characteristics of the existing fully isolated overhead contact system and then derives the projected system. A new silicone carbide power electronic and the necessary control algorithms for the direct integration of photovoltaic arrays are proposed and evaluated. The measurement of a first small volume 10kW prototype inverter shows that the integration can be done with high efficiency. - 190.A. Uphues, K. Nötzold, R. Wegener and S. Soter, "Crowbar-less ride through of asymmetrical gric faults with DFIG based WECS" in 2017 IEEE AFRICON, 2017, pp. 1026--1031.
Abstract:
Due to the increased renewable power penetration level renewable power plants have to provide low-voltage ride-through (LVRT) capability with simultaneous dynamic voltage support, to ensure the grid stability during grid faults. Concerning doubly fed induction generator (DFIG) based wind energy conversion systems (WECS) large electromotive forces and rotor currents, which may damage the rotor-side converter, or adversely affect the DFIG's controllability are induced into the rotor circuit in case of voltage dips. To handle and limit the rotor currents in case of asymmetrical voltage dips without crowbar triggering, a virtual resistance control approach based on the standard dq-control in the synchronous reference frame is discussed. The theoretical results are compared with those of more demanding virtual inductance control. The LVRT capability is verified with measurement results, recorded during a certification campaign at a 2.1 MW WECS concerning the Indian grid code.
