Projektarbeit

The measurement of the magnetic properties of electrical sheets is usually carried out according to standards. With the Epstein frame, the material is exposed to defined field strength by energizing a primary winding and the flux density is determined by measuring the induced voltage of a secondary winding. In order to quantitatively determine the field strength from the current, the sample must be fully enclosed by the primary winding and the coil geometry must be completely known. However, due to their design, some measuring devices do not have a continuous primary winding, which means that the field caused by the current cannot be quantified. At the interface between a sample and air, the boundary condition for the magnetic field is that the tangential component of the field strength does not change. By measuring the sample surface, conclusions can be drawn about the field in the sample. Hall effect sensors, sensors that are based on the magneto resistive (MR) effect and H-field coils are suitable for this purpose. The aim is to investigate which of the options are suitable for measuring the tangential field strength on the sheet metal surface. To do this, among other things, a circuit must be developed that processes the sensor signal. The results should be verified using the Epstein frame and a Teslameter.

PA 003

Auskunft und Betreuung:   M. Sc. Philipp Sisterhenn

Modulationsverfahren für 3-Level-Wechselrichter, insbesondere die Raumzeigermodulation, gehen von einer gleichmäßigen Verteilung der zur Verfügung stehenden Spannungslevel aus. Ist diese Spannungsverteilung gestört, verschieben sich die Raumzeiger der Schaltzustände auf komplexe Art und Weise, so dass sich die klassische Herangehensweise dermaßen komplex gestaltet, dass Sie umständlich und schwer zu beherrschen wird. In dieser Arbeit sollen Modulationsverfahren verwandter Topologien daraufhin untersucht werden, ob und inwieweit ihre Anpassung auf den 3-Level-Wechselrichter zu einem einfacheren und genaueren Modulationsverfahren führen kann. Bei den „verwandten Topologien“ handelt es sich um sogenannte Matrixumrichter. Moderne Modulationsverfahren für Matrixumrichter setzen keine Symmetrie der Spannungslevel voraus, weil sich diese Spannungslevel im Betrieb ohnehin ständig ändern.

Zur Erprobung der angepassten Modulationsverfahren soll ein einfaches Simulationsmodell in Matlab/Simulink erstellt werden. Das adaptierte Verfahren soll für den Fall einer symmetrischer Spannungsverteilung mit einem klassischen (z.B. Raumzeigermodulation) verglichen werden. Bei unsymmetrischer Spannungsverteilung ist zu überprüfen, ob sich Vorteile z.B. bezüglich des Oberwellengehalts der Ausgangsspannungen ergeben.

PA 005

Auskunft und Betreuung:   M. Sc. Marco Eckstein

Looking for bearing’s faults through the electrical machine’s signals using acceleration sensors is particularly the most common signal which is used in addition to the current signal, to find a relevant fault patterns. Based on the recent scientific publications and works, there should be noticeable changes in the harmonics’ amplitude at specific frequencies, namely, the so-called ‘natural frequencies’, which are defined based on the bearings rotation and its mechanical features like speed and dimensions.

However, processing the bearing’s acceleration signal from recently performed experiments, doesn’t confirm the theoretically derived natural frequencies. It means after processing the acceleration signals; not noticeable and somehow insignificant changes of the spectral amplitudes are seen at the natural frequencies, which can have multiple reasons, including low precision in the frequency’s equations.

The goal of this project work is to redefine the frequencies based on the fundamentals of mechanical rotation, model and simulate the bearings mechanically by the FEM software CREO under load to check out the acceleration and force signals and the validity of the new offered equations.

PA 004

Auskunft und Betreuung:   M. Sc. Shima Tavakoli

The operating behavior of electrical machines can be examined using special machine test benches. A machine test bench can be roughly divided into a mechanical structure, power components and the control part. For this work, the control unit for a three-phase inverter needs to be implemented on a STM32 microcontroller.

For an executable overall system, the hardware available is a Nucleo STM32F303RE evaluation board, the matching IHM08M1 inverter module and a PMSM as a test machine. The programming must be carried out using the STM32CubeIDE development environment. The aim is to make a technically sensible use of the hardware features available on the STM32 (timer, PWM, …) and to specifically divide the program’s timing in the software in order to have enough buffer of computing time for other tasks. Due to the existing hardware and the manufacturer’s sample software, some features are already known that can be used as a guide. In addition, a basic dashboard needs to be built using Node Red in the “STM32CubeMonitor” which will be used to control and monitor the system via a PC. In the end, there should be a functional inverter system that is controlled via a PC and is able to be expanded to include machine controls, measurements and other features in future works. Therefore, a detailed documentation must be prepared as part of the written elaboration.

Required Knowledge: Good experience in programming microcontrollers in the programming language C

PA 002

Auskunft und Betreuung: Dr.-Ing. Jens Igney / M. Sc. Philipp Sisterhenn

Classical modulation technique for power inverters use the triangular carrier signal modulation or the space vector modulation to generate the voltage pulse patterns. In general, these resulting voltage pulse patterns are non-optimal in view of the total harmonic distortion (THD) of the voltage pattern itself, but also non-optimal in view of the resulting current, even in steady state synchronized operation.

Because the voltage pulse patterns and the resulting currents are periodic in the steady state operation, the main tool for the analysis of the charactersitics is the Fourier series expansion. Therefore, the Fourier series expansion of the volage pattern can be used to analyse the spectral characteristics of the voltage pulse pattern, the THD of it and the THD of the resulting current.

This project aims to investgate the analytical description of different voltage pulse patterns in steady state operation of the power inverters. At first, voltage pulse patterns with quarter wave symmetry will be investigated, taking different numbers of pulses per half period into account. Secondly, pulse patterns with half wave symmetry will be constructed and analysed in view of their characteristics. Both types of pulse patterns with different numbers of pulses should be optimised to reach to least THD of the resulting current in different operation point, depending on the modulation index.

Besides single phase inverters, three phase inverters should be considered in the investigation. The power inverter switches will be modeled as ideal switches. The SicLab software environment will be used for building up the simulation models and to perform the analytic-numerical analyses. Theoretical derivations, the general and detailed findings and the developed software should be commented and documented precisely and in detail.

PA 001

Auskunft und Betreuung: Prof. Dr.-Ing. Ingo Hahn