Technologie TransferZentrum-Elektromobilität (TTZ-EMO)
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PyEMMO - a Python based software for the finite element modelling of electrical machines in ONELAB
(2023)
Multizieloptimierungen sind im Designprozess elektrischer Maschinen aufgrund stetig steigender Anforderungen an Wirkungsgrad und Leistungsdichte nahezu unabdingbar. Dabei bietet Open-Source Simulationssoftware die Möglichkeit lizenzkostenfrei Berechnungen zu parallelisieren und somit eine reduzierte Berechnungszeit zu erreichen. Dieser Beitrag stellt das hierfür initiierte Softwareprojekt PyEMMO (Python Electrical Machine Modeling in ONELAB) für die Finite-Elemente-Simulation elektrischer Maschinen im Open-Source-Programm ONELAB vor. Die objektorientierte Programmstruktur und die Ziele des Projekts stehen hierbei im Vordergrund. Des Weiteren wird auf den aktuellen Funktionsumfang eingegangen, welcher unter anderem die Geometriedefinition über ein Baukastensystem, das Simulationsdateninterface basierend auf dem JSON-Dateiformat und die Berechnung der Eisenverluste beinhaltet.
In lithium-ion batteries, depending on the requirements, many individual cells are connected in series and parallel. Despite very similar individual cell parameters after production, they can develop differently during the subsequent ageing process due to intrinsic and extrinsic influences. A pronounced parameter variation of the assembled cells ultimately leads to a reduced utilisation of the lithium-ion battery and thus also to a reduced lifetime. The aim of this work is therefore to gain a better understanding of the origin and development of parameter variation during the ageing process. The work is divided into three major parts. At the beginning, parameters such as capacity and internal resistance of 480 brand-new cells of one production batch are recorded. The obtained values allow the calculation of the production-related parameter variation of the cells. In order to investigate the development of the parameter variation during cell ageing, numerous ageing tests are carried out in this work. These are divided into single cell tests and module tests. With the help of single cell ageing tests, the development of the parameter variation of unconnected cells is investigated. Here, several cells are combined into groups and aged under identical conditions. In order to show the influence of different operating conditions on the parameter variation during single cell ageing, the cell groups are aged at different temperatures and different load currents. Finally, by ageing various self-built modules, the development of the parameter variation of cells connected in series and in parallel is investigated. By varying the load current and the number of cells connected in parallel, further dependencies are investigated. The measured data show that both the load on the cells and the ambient temperature have a decisive influence on the development of parameter variation. Operating conditions near the lithium plating boundary are particularly problematic. Since the onset of lithium plating varies slightly between the ageing cells, there are extreme differences in the ageing rate over a certain period of time. This ultimately leads to large parameter variations in the tests carried out. The cells used in this work are cylindrical cells in 18650 format with a nominal capacity of 2.6 Ah (Samsung ICR18650-26J). The high-energy cells consist of a NMC cathode and a graphite anode.
The production process of electrical machines is subject to manufacturing and material tolerances. These tolerances have an influence on both, the mean torque and the torque ripple. Consequently, they exert an active influence on the speed-torque map (operating points), as well as the equivalent circuit diagram parameters for a permanent magnet synchronous machine, and the operational behavior (efficiency, noise development) of the electrical machine. In addition to striving lower costs, there is a growing emphasis on achieving higher energy efficiency. Thus, an accurate prediction of machine parameters is still essential during the early development process, despite manufacturing-related deviations.
In this study, the prediction of machine parameters is demonstrated using the example of a PMSM.
In this work a new expansion measurement methodology for the detection of ageing mechanisms in lithium ion cells is described and evaluated. For this purpose, a polarization-optical homodyne Michelson interferometer with a resolution of approx. 10 nm was set up to allow measurements of different cell types, cell sizes, and cell chemistry within a Memmert IP55 climate chamber. The used interferometric measurement setup is ten times more accurate than measurement systems commonly used for battery measurements in the literature. The better spatial resolution of an interferometer setup enables the recording of the expansion response to short current pulses with low transferred charge. This offers the possibility to detect ageing mechanisms such as lithium plating within short measuring times. With this measurement setup, a lithium iron phosphate pouch cell from the company A123, with the model identification AMP20M1HD-A, is measured. First, an expansion measurement over a full charge and discharge cycle with a constant load of ± C 20 (b=1 A) is performed. Here, the cell undergoes an expansion of about 42 μm. Subsequently, the in this work proposed measurement methodology is presented to show the influence of effects such as the formation of overshooting graphite stages or lithium plating on cell expansion. For this purpose, at a residual capacitance of 50%, the cell is pulsed with current of different intensity I ∈ {±20A,±80A} for t = {240 s, 60 s}, at T = {10 ◦C, 20 ◦C, 30 ◦C}, respectively, and the mechanical response is recorded using the high accuracy interferometer setup. A mechanical relaxation of the cell after the pulses with a time constant in the range between 10 s and 20 s can be observed. It is shown that this relaxation behavior can be associated with effects of the anode known from the literature, such as the formation of overshooting graphite stages or lithium plating. These effects can be recorded by the very high-resolution measurement already with little transferred charge and within a short measurement time.
Verfahren zur phasenweisen Regelung der Schaltfrequenz bei Einsatz der Hysteresestromregelung SDHC
(2014)