Open Access

This paper presents a method of impedance analysis in power electronic systems during operation. The switching behavior of power electronic components causes harmonic excitation in a system. These harmonics in voltage and current are analyzed with a polyphase filter bank. Afterwards they are used to calculate the system’s frequency dependent impedance. The method is validated with simulations and verified by measurements of a real power converter. The results give incentive for further researches.

(English) When using voltage source converters (VSC) to control the load flow between the DC voltage circuit and n-phase AC consumers/generators, distortion currents/voltages occur due to the principle involved. These describe the deviation of the real, measurable signal from its ideal, desired course. The distortion voltages occurring at the AC-side connection points of the VSC correspond to the deviation from the specified set voltage. At the DC-side connection point strong distortion currents are superimposed on the direct current emitted or absorbed by the VSC. Within the scope of this work, the emergence of the DC-side distortion currents, caused by the switching mode of operation of the VSC, based on corresponding literature sources, is discussed. The consideration here is limited to the differential mode components of the currents mentioned, a common mode consideration is not carried out. Criteria for describing the DC-side distortion currents and factors for influencing these criteria are derived from the results of the investigations carried out. For a given system and operating range, the distortion current stress caused by the VSC can be varied by adapting the control method used. For this purpose, different control methods found in the literature are selected and the operating point-dependent distortion current stress caused by them is determined analytically. To verify the results, a simulation model is developed and tests are carried out on an experimental test setup. The VSC is operated with a modulator-based control method as well as with a direct current control method. The results are compared regarding the DC-side distortion current. Namely, the control methods used are Space Vector Modulation (SVM) and Scalar Hysteresis Control (SHC). The latter was developed at the Technical University of Applied Sciences Wuerzburg-Schweinfurt. If the DC-side distortion current stress caused by the VSC is known, a filter can be designed that reduces the interference emission of the VSC to a specified level. As a level for the remaining interference emission, the remaining voltage ripple at the DC-side connection point of the filter is usually used in regulative specifications. Passive filters consisting of one or more capacitors of the same or different type are usually used for this purpose. This filter structure is described below as conventional structure. The different variants are presented accordingly and the filter capacitor is designed analytically/numerically on a concrete example for the DUT operated with SHC as well as SVM. Concepts known from literature for reducing the passive filter effort are presented and their effects on the DC-side distortion current load are described analytically. The concepts presented are divided into the categories of horizontal and vertical extension of the VSC as well as extension by downstream active components. In the second part of the work, a non-linear hybrid filter consisting of an actively controlled four-quadrant controller and two passive filter stages is designed and a methodology for the design of the components is developed. Furthermore, a modulation scheme with superimposed control for the use of the four-quadrant controller as an active filter is developed. The methodology for designing the filter is applied to the DUT used in this work as an example. The verification of the calculated results is carried out using a simulation model and an experimental test setup. Finally, the presented and more detailed passive filter variants as well as the developed non-linear hybrid filter are compared with each other in terms of construction volume and interference immunity. This shows that the presented non-linear hybrid filter has a significantly better interference immunity and a lower tendency to oscillate compared to passive filters. As a result, a more stable filter effect can be expected, especially when used in dynamic systems or systems with unknown dynamic behaviour.

In speed control of permanent magnet synchronous motors, the measured position signal is usually used for motor commutation and speed calculation. Since the position and speed signals are fed back to the controller, a sensor fault during operation is a severe problem. This contribution proposes a simple linear estimation method that reconstructs rotor position and speed. A comparison between measured signals and estimates allows to detect faults during operation. Furthermore, the estimated signals are used for reconfiguration after the occurrence of a fault. The fault detection logic is based on an adaptive threshold facilitating an operating point-dependent compromise between robustness against uncertainties and sensitivity to faults. Measurement results show that no faults are detected during fault-free operation, whereas the proposed algorithm instantly recognizes the sudden supply voltage outage of the used incremental encoder. The investigated reconfiguration mechanism allows for the control of the motor at medium and high speeds after the detection of a fault. This can be used to decelerate the motor in a controlled manner.

Der Einsatz von elektrischen Maschinen in Hybrid- und Elektrofahrzeugen bedingt besonders hohe Anforderungen bezüglich Leistungsdichte und Wirkungsgrad bei gleichzeitig hohen zu produzierenden Stückzahlen. Im Bereich der elektrischen Traktionsmaschinen für Kraftfahrzeuge haben sich in den vergangenen Jahren Wicklungen aus Formspulen (z. B. in der Ausführung als Hairpin-Wicklung) gegenüber herkömmlichen Einzugswicklungen aufgrund einiger spezifischer Vorteile weitgehend durchgesetzt. Die Kombination aus vergleichsweise großem Leiterquerschnitt der Formspulen und hoher Grundfrequenz der elektrischen Speisung führt aber dazu, dass die Stromverdrängung in der Wicklung im Allgemeinen nicht mehr vernachlässigbar ist und zu einer deutlichen Erhöhung der Stromwärme führen kann. Das Ziel der vorliegenden Arbeit ist die Untersuchung der Stromverdrängung am Beispiel von Hairpin-Wicklungen und die Entwicklung einer hybriden Berechnungsmethode. Dazu werden zunächst die Ursachen der Stromverdrängung mit der eindimensionalen analytischen Berechnung betrachtet. Wie sich zeigen wird ist diese Methode bei den betrachteten, hochausgenutzten elektrischen Traktionsmaschinen jedoch nur eingeschränkt anwendbar, sodass die gewonnenen Erkenntnisse mit der 2D-FEM erweitert werden. Die entwickelte hybride Methode trennt die Berechnung der Stromwärme in den Spulenseiten der Nut von der Berechnung der Stromwärme in den Leitern des Wickelkopfes. Zur Berechnung der Stromverdrängung in den Spulenseiten der Nut wird zunächst die zeitveränderliche Längs- und Querkomponente des Nutstreufeldes mit einem magnetischen Ersatzschaltbild ermittelt und daraus die Stromverdrängung bzw. die zusätzliche Stromwärme in den Spulenseiten mit einem analytischen Ansatz berechnet. Die Stromverdrängung in den Leitern des Wickelkopfes wird mit der 3D-FEM untersucht und aus diesen Erkenntnissen wiederum eine hybride Berechnungsmethode entwickelt. In diesem Fall wird zur Berechnung des magnetischen Feldes im Stirnbereich das Gesetz von Biot-Savart numerisch gelöst und die Spiegelleitermethode angewendet. Die Wirbelstromdichte in den Leitern wird anschließend analytisch berechnet. Beide hybride Methoden werden in dieser Arbeit anhand von ungesehnten Hairpin-Wicklungen vorgestellt, sind aber grundsätzlich auf beliebige Anordnungen übertragbar. Den Abschluss der Arbeit bildet die Messung des magnetischen Feldes im Stirnbereich und die temperatur- und frequenzabhängige Messung des Stromverdrängungsfaktors bei einem Stator mit Hairpin-Wicklung.

(English) Lithium-Ion Batteries (LIBs) are being used in more and more areas of application. At the same time, their chemical composition and their designs are constantly evolving. Major developments are also taking place in the field of Battery Management Systems (BMSs), which are essential for the safe operation of LIBs. The focus is on intelligent charge redistribution between individual cells, called Active Balancing (AB). This thesis deals with the possibilities and limitations of AB. An empirical long-term experiment provides new insights into the ageing behaviour of batteries that are actively balanced during their entire service life. The main objective of this work is to to demonstrate influences on the ageing behaviour of batteries that are still unknown at present. A literature study shows that previous work in this area is often based on theoretical approaches and rarely has a functional proof through measurement results. Most significant statements from literature are examined. These include the increase in discharge capacity, energy efficiency and service life associated with AB, as well as lower parameter variation of the individual cells installed in the battery. Before starting the empirical experiment, the current state of the art is captured and a universal AB topology is selected from a large number of known systems. The operating behaviour as well as the balancing algorithms are explained in detail in order to be able to understand the influences occurring during the ageing of the batteries. The ageing experiment itself is a comparison test between commercial Passive Balancing (PB) and the novel AB. Two identical battery packs are aged under uniform conditions, but with the two different BMSs mentioned above. At the end of the ageing process, the battery packs are disassembled and the parameters of all individual cells are determined for further investigation. The main contribution of this work is the proof of effects through AB, especially with large battery loads. Both the increase in discharge capacity and the service life are demonstrated. The work shows how parameter variation of individual cells can be made visible during operation. It also presents diagnosis and calculation methods. The energetic efficiency of the batteries cannot be increased, since the self-consumption of the power electronics of the AB system is always higher than with PB. However, the overall efficiency of the battery increases due to an increase in capacity and an extension of the service life. The thesis also shows that with lower battery loads, the use of AB is not beneficial any more or may lead to negative effects. In such applications conventional PB is sufficient. The results obtained during pack ageing are additionally substantiated and extended by the measurement results of the individual cells. At the end of the thesis, all results and contributions are summarised. Suggestions for optimisation as well as further research ideas are presented as a possible starting point for further scientific studies. (Català) Les bateries d’ions de liti (Lithium Ion Batteries, en anglès) s’usen en més aplicacions. Al mateix temps, la seva composició química i dissenys estan en evolució constant. Els sistemes de gestió del bateries (Battery Management Systems, en anglès), que són essencials per l’operació de les LIB, també estan en constant evolució. El focus principal està en la distribució intel·ligent de càrrega elèctrica entre cel·les individuals, l’anomenat balanceig actiu (Active Balancing, en anglès). Un assaig empíric, de llarga durada, com el dut a terme en aquest treball, dona molt informació en el procés d’envelliment de les cel·les durant tota la seva vida. El principal objectiu d’aquest treball és demostrar les influències encara desconegudes en el procés d’envelliment de les cel·les. L’estudi de la literatura mostra que el treball previ en aquesta àrea està sovint basat en aproximacions teòriques i estranyament ensenya resultats empírics que ho corroborin. En aquest treball s’examinen la majoria de presumpcions que es poden trobar a la literatura. Aquestes inclouen l’increment en la capacitat, l’eficiència energètica i la vida útil associada a un balanceig actiu de les cel·les, així com la reducció de la variació dels paràmetres de cada cel·la en una bateria. Abans de procedir amb l’experiment empíric, es revisa l’estat de l’art en els aspectes fonamentals per aquest estudi. També se selecciona una tipologia de sistema de balanceig actiu per tal de realitzar l’experiment. El treball detalla el procediment d’operació així com l’algoritme de balanceig actiu implementat per tal d’entendre els fenòmens que influencien la degradació de les cel·les durant la seva vida. L’experiment d’envelliment és una comparació entre un sistema de balanceig passiu (Passive Balancing, en anglès) i un de balanceig actiu. Per això s’escullen dues bateries idèntiques, però gestionades diferentment per dos sistemes de gestió diferents. Al final de l’assaig, les bateries es desmunten i s’analitza cada cel·la de forma individual per tal de determinar-ne els seus paràmetres i el seu envelliment. La principal contribució d’aquest treball es el demostrar els efectes del balanceig actiu , sobretot en bateries amb una càrrega elevada. El treball demostra que el balanceig actiu millor gla capacitat de la bateria i la vida útil. El treball també mostra com la variació dels paràmetres de les cel·les es pot fer visible durant la seva operació. També presenta nous mètodes de diagnosi i càlcul d’aquests paràmetres. L’eficiència energètica de les bateries no es pot augmentar degut al consum propi i les pèrdues del sistema de balanceig actiu basat en electrònica de potencia. Si que augmenta l’eficiència global de la bateria, ja que augmenta la seva capacitat i la vida útil. El treball també mostra que en bateries sotmeses a baixa càrrega, el balanceig actiu no aporta cap avantatge respecte el balanceig passiu. Fins i tot en algunes situacions, els efectes del balanceig actiu són negatius. En aquestes aplicacions, es recomana l’ús d’un sistema de balanceig passiu. Els resultats obtinguts durant l’assaig de la bateria queden reforçats quan es fa l’anàlisi de cada cel·la de forma individual. Al final del treball, es resumeixen tots els resultats a més de proporcionar suggereixes per la optimització així com possibles línies de futures investigacions

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.

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.