05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Inductive electrically excited synchronous machine for electrical vehicles : design, optimization and measurement(2023) Müller, Samuel; Maier, David; Parspour, NejilaThe demand for electric machines has been rising steadily for several years-mainly due to the move away from the combustion engine. Synchronous motors with rare earth permanent magnets are widely used due to their high power densities. These magnets are cost-intensive, cost-sensitive and often environmentally harmful. In addition to dispensing with permanent magnets, electrically excited synchronous machines offer the advantage of an adjustable excitation and, thus, a higher efficiency in the partial load range in field weakening operation. Field weakening operation is relevant for the application of vehicle traction drive. The challenge of this machine type is the need for an electrical power transfer system, usually achieved with slip rings. Slip rings wear out, generate dust and are limited in power density and maximum speed due to vibrations. This article addresses an electrically excited synchronous machine with a wireless power transfer onto the rotor. From the outset, the machine is designed with a wireless power transfer system for use in a medium-sized electric vehicle. As an example, the requirements are derived from the BMW’s i3. The wireless power transfer system is integrated into the hollow shaft of the rotor. Unused space is thus utilized. The overall system is optimized for high efficiency, especially for partial load at medium speed, with an operation point-depending optimization method. The results are compared with the reference permanent magnet excited machine. A prototype of the machine is built and measured on the test bench. The measured efficiency of the inductive electrically excited synchronous machine is up to 4% higher than that of the reference machine of the Bayerische Motoren Werke AG (BMW) i3.Item Open Access Accelerated 3D FEA of an axial flux machine by exclusively using the magnetic scalar potential(2023) Schäfer, Adrian; Pecha, Urs; Kaiser, Benedikt; Schmid, Martin; Parspour, NejilaThis article focuses on increasing the computational efficiency of 3D multi-static magnetic finite element analysis (FEA) for electrical machines (EMs), which have a magnetic field evolving in 3D space. Although 3D FEA is crucial for analyzing these machines and their operational behavior, it is computationally expensive. A novel approach is proposed in order to solve the magnetic field equations by exclusively using the magnetic scalar potential. For this purpose, virtual variable permanent magnets (vPMs) are introduced to model the impact of the machine’s coils. The effect on which this approach is based is derived from and explained by Maxwell’s equations. To validate the new approach, an axial flux machine (AFM) is simulated using both 2D and 3D FEA with the magnetic vector potential and current-carrying coils as a reference. The results demonstrate a high level of agreement between the new approach and the reference simulations as well as an acceleration of the computation by a factor of 15 or even more. Additionally, the research provides valuable insights into meshing techniques and torque calculation for EMs in FEA.Item Open Access An easily scalable dynamic wireless power transfer system for electric vehicles(2023) Noeren, Jannis; Parspour, Nejila; Elbracht, LukasThis article deals with a LCC-LCC compensated dynamic wireless power transfer system for electric vehicle charging applications. The presented prototype system allows for a power transfer of about 10 kW at 20 cm coil copper to copper distance. With just one circular pickup coil and a very straightforward control scheme, a new coil arrangement enables a seamless power transfer. Furthermore, the system’s design power level is easily adjustable by the size of the the pickup coil. The hardware architecture as well as the software functionality are described in detail. A 20 m test track was built up according to the outlined principle. By measuring the transmitted power, the efficiency and the interference between the primary segments and its effect on the inverter currents are examined. The results show an effective DC to DC efficiency in the range of 91 to 92% and a power fluctuation of approximately 25%.Item Open Access A review of electromagnetic simulation and modelling approaches for the research on axial flux synchronous machines(2024) Schäfer, Adrian; Pecha, Urs; Parspour, Nejila; Kampker, Achim; Born, Henrik; Hartmann, Sebastian; Franke, Jörg; Baader, Marcel; Hahn, RomanExtensive electromagnetic (EMAG) studies are necessary to fully realize the potential of axial flux machines (AFMs). However, the disc-shaped air gap and the complex three-dimensional path of magnetic flux pose challenges in modelling AFMs compared to conventional radial flux machines. This study reviews current research on EMAG modelling and simulation of AFMs, highlighting the need for tools that address AFM-specific effects. Existing approaches are analysed based on the requirements composed by fundamental objectives of EMAG simulations and AFM-specific effects, revealing limitations in flexibility and the ability to capture emerging trends in the field of AFMs. While computationally expensive 3D finite element analysis (FEA) offers comprehensive flexibility in EMAG modelling, it lacks efficiency to carry out extensive studies on such trends. Therefore, there is a need to either further accelerate 3D FEA or to increase the flexibility of existing alternatives to facilitate and thereby promote research in the field of AFM and other 3D flux machines. While the integration of some production-specific effects, such as manufacturing tolerances, already is investigated for EMAG simulations of AFMs the future research on the early estimation of manufacturability based on EMAG simulations is crucial for evaluating designs and anticipating manufacturing influences.Item Open Access Voltage balancing of a Pi-type multilevel converter for charging electrocaloric capacitors(2025) Bennour, Ines; Mönch, StefanElectrocaloric solid state heat pumps provide a sustainable solution for cooling and heating systems powered by electricity. The electrocaloric effect is a reversible temperature change when the electric field changes in multilayer capacitors made of special dielectric functional materials. It can be transferred into an efficient solid-state heat pump system but requires highly efficient power electronics. High efficiency has already been achieved with multilevel converters with ideal capacitive loads. However, when operating with real, lossy and non-linear electrocaloric components as a load, the internal buffer voltages drift away due to uneven charge distribution across the capacitors. The main idea of this paper is to investigate and solve the unbalancing problem with a purely software-based control technique: Intentional unsymmetrical level-skipping can effectively charge or discharge the buffer voltage. The new balancing operation is experimentally demonstrated with a four-level Pi-type GaN-based multilevel converter, hysteretic current control for zero voltage switching, and an electrocaloric ceramic capacitive load (10µF, 120V, 0.5Hz system frequency). The 4 level balancing operation reduced the power loss by 24% (compared to 2 level), and enabled continuous operation with stabilized buffer voltages.Item Open Access A 2.3 mW 1 MHz digitally isolated hysteretic current control circuit with shunt-based current sense amplifier(2025) Öhrlein, Julius; Söllner, Adrian; Bennour, Ines; Mönch, StefanHysteretic current control (HCC) of the inductor current in switched-mode power converters enables fast and direct control and requires high bandwidth isolated current sensing. However, analog-isolated Hall or TMR sensors consume a high power (typ.: 15 mW at 1.5 MHz). This work presents a digitally isolated HCC circuit using a shunt resistor, differential amplifier and two comparators with selectable reference values. A 1 MHz bandwidth HCC circuit was built and applied to a half-bridge converter, consuming only 2.3 mW during operation (from which 1 mW are from an isolated 5 V power supply).Item Open Access Optimal transistor dimensioning in T-type topology for reduced quasi-2-level switching loss(2025) Söllner, Adrian; Jie, Chengcong; Mönch, StefanA quasi-2-level switching T-type topology reduces hard-switching loss compared to half-bridges, but requires more semiconductor area. This work shows that the middle transistor can be dimensioned smaller than the high/low-side transistors, which further reduces both the switch node capacitance and switching loss. The paper also presents a scalable transistor model, which is used in simulations of inductive-load hard-switching to determine switching losses and reveal a loss-optimal transistor dimensioning. Furthermore a double pulse setup (600 V-rated GaN HEMTs in a T-type topology) with 2 ground referenced shunts is proposed to determine switching energy of middle and low side transistors simultaneously. To verify the concept of loss-optimal transistor dimensioning in Q2L T-type topology, switching energy was measured at 200 V and 1 A, with the middle transistors area reduced by half compared to high/low side, resulting in a measured reduction from 4.44 µJ to 2.18 µJ (-51%) which is similar to the simulated reduction (2.39 µJ to 1.43 µJ, -40%). This method allows reduction of Q2L switching-loss with optimal transistor area and can be used for a wide range of applications.