Examensarbeten för masterexamen // Master Theses
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Browsar Examensarbeten för masterexamen // Master Theses efter Program "Electric power engineering (MPEPO), MSc"
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- PostAdvanced Cooling of Electric Machine in a Hybrid Vehicle Application(2014) Fr öb, Johan; Lykartsis, Odyssefs; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalTransportation sector is consuming a large portion of the total energy used by the humans. Today, most of the commercial vehicles are driven by internal combustion engines. Replacing them with electrical machine could have a large impact in the environment. But there is still room for improvement in the electric machines in order to replace the internal combustion engines. The electrical machines that are used in the automotive industry use permanent magnets in their rotors. They have a number of advantages such as very good efficiency and high power density. On the other hand, sensitivity of the magnets in high temperatures and their price is the major drawbacks of permanent magnet machines. The magnets cannot operate in high temperatures because they suffer from demagnetization. To deal with this problem, today, high temperature grade magnets with a lot of segments are used. In this thesis an oil spraying technique is used to cool the magnets in a safe operating temperature, increase their performance and also reducing their manufacturing cost. The analysis is based on theoretical calculations and experimental results from a test rig that was designed and constructed within the thesis. The oil-spraying cooling system, was designed to spray oil on the inside of the rotor of the electrical machine. Due to the high rotational speed the oil forms a thin film that absorbs the heat generated by the magnets. In the thesis a cylinder with an external heat source that simulated the actual rotor was used for evaluation. The actual losses of the magnets in an electrical machine was calculated for different operation points and segmentation of the magnets. Then the temperature of the magnets was calculated, by developing a thermal model, with and without oil spraying. The results showed significant drop in the temperature of the magnets as well as reduction in the number of segments.
- PostExperimental Characterization of Li-ion Battery cells for Thermal Management in Heavy Duty Hybrid Applications(2017) Lidbeck, Anton; Syed, Kazim; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalThe performance and lifetime of lithium ion (Li-ion) batteries are highly dependent on the internal operating temperature which makes thermal characterization of battery cells necessary. Therefore, the main focus of this thesis work was to characterize pouch and prismatic Li-ion cells by designing and conducting experiments to measure thermal parameters. The specific heat capacity was quantified as well as the heat conductivity in three dimensions. In addition, the heat generation from the cells was measured for different load cycles. Subsequently, the determined thermal parameters were inputs in a simulation model to determine the internal peak temperature of the cell during different load cycles. The experiments were carried out by using a custom-designed isothermal heat conduction calorimeter (IHC). This calorimeter was modified for measurement of individual thermal parameters. The modified setup was verified using available sample materials and subsequently applied for measurements on the Li-ion cells. The heat generated within the cells was measured for constant current rates and a dynamic operation cycle. The through-plane thermal conductivity for the provided pouch cell was measured to be lower than the in-plane (0.7Wm−1 K−1 compared to 20-30Wm−1 K−1). In addition, the specific heat capacity was measured to be 1100 J kg−1 K−1 for a pouch cell and a prismatic cell. Lastly, the heat generated by the cells was measured between 10mW to 30W. To conclude, the heat generation and specific heat capacity was measured successfully for both the pouch and prismatic Li-ion cell. The methods for thermal conductivity in through-plane and in-plane were utilized for the pouch cell. However, the proposed methods for thermal conductivities were found to be inapplicable for prismatic cells due to the conduction through the aluminum casing. Nevertheless, this opens up opportunities within the thermal characterization of Li-ion batteries.
- PostOn-board impedance diagnostics method of Li-ion traction batteries using pseudo-random binary sequences. Method evaluation and feasibility study of concept.(2015) Geng, Zeyang; Savvidis, Charalampos; Chalmers tekniska högskola / Extern; Chalmers University of Technology / ExternalThis thesis deals with the on-board impedance measurements of Li-ion batteries on hybrid electric vehicles/electric vehicles by using pseudo-random binary sequences (PRBSs). The impedance of the battery can be related to its state of charge but the accurate impedance measurements are difficult to perform in the vehicles. By using an excitation signal like PRBS, it is possible to extract the impedance information of the battery packs. Both experiments and simulations are performed with different set-ups to verify the PRBS method. A non-parametric method is used to process the data and extract the impedance measurement. Experiments in the laboratory at different SOC levels and temperatures are made to validate the PRBS method. In the simulations, the noise sensitivity is analyzed. It is shown that the PRBS method can produce a valid electrochemical impedance spectrum in a limited frequency range, similar to the result from a high accuracy laboratory impedance analyzer. The method is stable at different SOC levels and temperatures. However, the battery impedance at high frequency is difficult to obtain with the PRBS method in the experiments. A simulation of the excitation signal in the vehicle is performed where the electric motor is used as the load. It shows that it is possible to some extent to use the drive line in a hybrid electric vehicle/electric vehicle to perform an on-board battery impedance measurement.