Examensarbeten för masterexamen


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    The design and usability of an eHealth demonstrator aimed to facilitate the prevention and care of persons with diabetes at risk to develop diabetic foot ulcers
    (2023) Ravichandran, Shivani; Chalmers tekniska högskola / Institutionen för elektroteknik; Candefjord, Stefan
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    Design And Analysis Of Wireless Power Transfer Using High Frequency Resonant Inductive Coupling By Changing The Coil Geometry
    (2024) Gouthamas, Nagendra; Bandi, Adarsh; Chalmers tekniska högskola / Institutionen för elektroteknik; Thiringer, Torbjörn; Thiringer, Torbjörn; Larsson, Fredrik
    Abstract In this thesis, we have developed a wireless power transfer system for a space of dimensions (15cm x 15cm x 15cm), utilizing a series-connected transmitter (Tx) coil to generate an equally distributed electromagnetic field inside the space. This field can be picked up by a solenoid receiver (Rx) coil placed anywhere within the space to power a DC load. To develop the proposed system, we have studied a conventional wireless power transfer system fromWurth Electronics and investigated various coil geometries for both Tx and Rx. The conventional wireless power system has been examined regarding the influence of coil geometry, alignment between the transmitter (Tx) and receiver (Rx), as well as the coil parameters on efficiency. The wireless power system from Wurth Electronics is tested with different Rx coil geometries to evaluate interoperability between various Tx and Rx coil geometries, as well as to compare the coupling coefficient and magnetic field density of different Rx coil geometries with misalignment in order to evaluate most suitable Rx coil geometry for the proposed wireless power system. The different Rx coil geometries investigated are: concentric, solenoid, and center-tapped circular coil. The comparison is based on different alignment conditions between the transmitter and receiver coils. We find, from the results obtained by investigating different Rx coil geometries with the conventional system, that the solenoid coil geometry with a core provides a stable coupling coefficient under various misalignment conditions. Thus, the solenoid Rx geometry can be optimized to enhance coupling between the transmitter and receiver coils. Additionally, test results show that the use of center-tapped circular coils in wireless power power system helps in improving range from 30mm to 180mm compared to conventional wireless power system with concentric coils. However, the improved range is only achievable with significantly higher number of coil turns compared to concentric coils which reduces efficiency. Also, a unique BJT based automatically switching transmitter circuit is required for the center-tapped circular coils which makes it a non-viable solution due to inefficiency of the BJTs. Further a suitable transmitter coil geometry is investigated for use in combination with the solenoid receiver to demonstrate the proposed wireless power system within a space of dimensions (15 cm x 15 cm x 15 cm). Three different transmitter coils are investigated: the concentric coil, 2-series connected concentric coil, and 8-series connected concentric coil. A half-bridge transmitter circuit is designed to drive the various transmitter coils. The experimental and simulation results indicate that the concentric transmitter coil with a large diameter enhances high power transfer and better range due to a more effective distribution of the magnetic field. However, when using a solenoid receiver coil, the power transfer efficiency drops by 28% compared to the efficiency of 75% under aligned operation. Consequently, the concentric transmitter coil is designed with the coil turns distributed into smaller areas, forming a 2-series connected coil. Test results reveal that it was possible to transfer 10W of power at an efficiency of 75% when the coils were perfectly aligned. In contrast, when the coils were misaligned, power transfer efficiency of up to 48% was achieved. This is in contrast to the power transfer efficiency of 6% under misaligned conditions in the conventional wireless power system. The 2-series connected concentric Tx coil is then extended to an 8-series connected concentric Tx coil to form a space of dimensions (15 cm x 15 cm x 15 cm) in combination with a solenoid Rx coil. Simulation results indicate that the coupling coefficient between Tx & Rx improved by approximately 11% and measurement results show that power transfer efficiency improved by 4% compared to the 2-series connected concentric Tx coil. Similarly, when the solenoid Rx coil was rotated or misaligned with the Tx coil, the efficiency improved by approximately 33% compared to the 2-series connected concentric Tx coil. The increase in efficiency and coupling with Tx and Rx is mainly due to distribution of coil turns into smaller areas and then connecting them in series which improved the magnetic field distribution compared to other coil geometries. Hence, the 8-series connected concentric coil as Tx and solenoid as Rx are selected as the suitable Tx and Rx coils, respectively, for the proposed wireless power system. In comparison to the conventional wireless power system, the efficiency remains approximately the same at 80% when the coils were perfectly aligned and efficiency improved by more than 60% when the coils were misaligned.
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    Modelling and Simulation of DC/DC Converter-Based Active Cell Balancing for Battery Management Systems
    (2023) GANGAMAGALA MAHANTHAPPA, VIKAS; SOLLAPURA VASANNA, SRINIDHI; Chalmers tekniska högskola / Institutionen för elektroteknik; Zou, Changfu; Li, Yang
    Abstract The transition to sustainable transportation was initiated to mitigate the effects of global warming and decrease CO2 emissions. Electric vehicles are at the forefront of this revolution and rapid technological advancements have been made in the development of electric powertrain’s components, particularly lithium-ion (Li-ion) batteries. These breakthroughs have played a significant role in increasing vehicle performance and range, prompting automotive companies to accelerate their transition to more sustainable vehicles. Li-ion batteries are prominent in their specific energy and specific power while the battery pack comprises low-voltage battery cells connected in series and parallel to meet the voltage and current requirements of the electric vehicles. However, since the cells are limited by voltage and capacity, a serious inconsistency between the cell’s voltage and state of charge (SoC) is generated because of the manufacturing inconsistencies of the individual cells in the battery pack. This leads to growth over time after a number of charging and discharging cycles because of different self-discharge rates, internal resistance, and operating temperature, which will affect the efficiency and life of the entire battery pack. It has become inevitable to keep the cells balanced to achieve the effective usage of energy and to enhance the battery life. This thesis starts with a comprehensive literature study and investigation of different types of cell balancing techniques with a focus on converter-based active balancing. A choice has been made after evaluating the performance and suitability of different converters considering the balancing method, balancing speed, balancing time, and control complexity. In MATLAB/Simulink, a bi-directional buck-boost converter was designed and simulated by integrating with the battery string, performing energy exchange between cells with different SoCs using a state-space modeling approach and cascaded PID control. An easy-to-implement and effective algorithm has been developed, tested, and validated to perform the balancing action in various operating scenarios.
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    Comparison between two-level and three-level DC/DC converters
    (2024) Jiang, Tianche; Chen, Mingshan; Chalmers tekniska högskola / Institutionen för elektroteknik; Beza, Mebtu; Parastar, Amir
    Abstract As automotive industry is developing rapidly, electric vehicles (EVs) have became a popular idea for green transportation due to its zero tailpipe emissions. One of the key parts on the EV board is the step-down DC/DC converter which is used to transfer power from high-voltage side battery to low-voltage side battery. To protect batteries on both sides, this DC/DC converter is always selected as isolated buck converter. This thesis project simulates, analysis and compares two-level and three-level isolated topologies, which are phase-shifted full bridge (PSFB) and T-Type converters in terms losses, efficiency and cost. In addition, since semiconductor technology is also growing quite fast, the new switching technology is used in selected topologies to check the difference between new switching device technology and traditional switching devices. Firstly, the operation principles of different topologies with voltage, current waveform and parameter selection are presented, which is followed by the theoretical comparisons about transformer turns ratio, voltage stress, current waveform with rms current, MOSFET losses, transformer design and its losses calculation. In order to have more realistic results and a fair comparison, simulation of different topologies with same input and output voltage is done with PSpice. Then, the data exported from simulations are used to calculate MOSFET losses and efficiency while the transformer loss calculation is based on both simulation data and real model. The final results show that PSFB has high efficiency while all topologies are operating with the same switching techniques, but T-Type converter has potential to increase efficiency by replacing the middle bridge SiC MOSFETs with Si MOSFETs.
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    Second Life for Commercial Vehicles Onboard Charging Electrical Power System
    (2023) Voppu Muralikrishna, Ajay Krishna; Ganesh, Viswanathan; Chalmers tekniska högskola / Institutionen för elektroteknik; Liu, Yujing; Isaksson, Björn
    Abstract The study begins by analyzing market studies to gauge the demand for repurposed OCEPS and this evaluation aims to determine the market’s readiness for such a transition. Moreover, the research conducts a thorough examination of existing OCEPS designs and their limitations. This analysis is crucial for proposing improvements that enhance overall efficiency, calculate losses accurately, and optimize performance. The intention is to ensure that repurposed DC chargers not only match technical requirements but also surpass previous models in energy efficiency and reliability. The study begins by examining the state of onboard charger technology highlighting its crucial role in EV performance and the challenges it poses in terms of environmental impact and economic sustainability. Recognizing that onboard chargers often outlast the vehicle this investigation explores the potential for repurposing or reusing these chargers for purposes thereby contributing to a more circular and sustainable economy. A significant contribution of this study is the development of a sustainable business model tailored to the repurposing process. This model seeks to combine economic feasibility with circular economy principles by leveraging market opportunities and addressing environmental concerns through efficient resource utilization and waste reduction. It then delves into the evaluation of current designs and the suggested improvements, highlighting potential enhancements in technical efficiency. Lastly, the discourse revolves around the innovative sustainable business model, which harmonizes economic viability and ecological responsibility. The research findings not only reveal the potential of onboard chargers but also propose a systematic framework for identifying and implementing second life opportunities, within the electric mobility ecosystem. The study’s implications go beyond the concerns of EV technology. Provide insights, into broader sustainability practices and the circular economy. If stakeholders, in the electric vehicle industry embrace the idea of giving onboard chargers a life they can contribute to a sustainable future while tackling the challenges posed by electronic waste. In summary, this thesis explores the conversion of OCEPS into DC chargers through a circular economy lens. By evaluating market demand, improving designs, and proposing a sustainable business model, the study bridges technological advancement and sustainability, fostering economic growth while respecting environmental balance.