A mobile sensing station is aimed to be released to the market to various engineers. Leading up to this, three separate groups are each responsible for the design choices. This report shall expound on the design choices contributing to the power supply module along with the complete hardware structure. These design choices are bound to a program of requirements based on the group's final goal.

The design choices were justified through rudimentary circuit theory, mechanics and trigonometry. Programming of these design choices were done using C in adherence to using the ESP32-C3 chip. Theories such as numerical methods come into light briefly. Limitations were found to the design choices such as the prohibition to use Li-ion batteries due to safety precautions, which affected the design choices significantly.

We have assembled and tested the power supply PCB, added temperature sensing capabilities, taken various measurements (voltage, current, temperature and SoC) and integrated code with other subgroups. For the hardware, we have made made an enclosure for all the electronics along with a drivetrain system, mostly using 3D printing technology. A first full system integration was not realized at the time of this report. The results show that we have sufficed most of the points in the program of requirements for both the power supply and hardware design. In the end a driving demo version has been reliased. Because of this, a fully functional system integration has been left at a future implementation. ... Read more

As renewable energy sources and DC energy storage continue to increase in modern power systems, the power electronic converters required to interface them with existing power grids are also rapidly increasing. This is resulting in increasing amounts of the total power exchanged on the grids being converted between DC and AC. Additionally, the majority of today's grid loads ultimately convert their input power to some form of DC whether they are connected to an AC or DC grid. Therefore, the concept of DC grids is becoming more attractive for applications such as DC distribution systems and electric vehicle charging stations. However, the existing AC grids will continue to play a fundamental role in the power infrastructure. Therefore, it is, important to consider how LVDC distribution grids will be connected to, and exhange power with, the AC grid. A transformerless interface between LVDC distribution grids and the LV AC grid via a power electronic converter is an attractive option in terms of size and cost reduction. However, the challenge of ground leakage current is a major challenge for such an interface.

This thesis assesses the different possible three-phase DC-AC converter topologies for a transformerless interface between a bipolar DC microgrid and the LV AC grid. The DC-AC converter modulation is explored to understand the challenges of ground leakage current and determine the feasibility of a transformerless interface. A detailed analysis of the common-mode voltage, common-mode impedance and resulting circulating currents in a grid-tied DC-AC converter is performed. The effect of this circulating current on AC grid protection equipment is considered.

A survey of converter modulation methods for common-mode reduction and DC bus voltage balancing is conducted. Simulations are used to verify the performance of the different modulation methods in terms of common-mode reduction and DC balancing capabilities in the bipolar DC grid. A new modulation method is proposed for simultaneously mitigating ground leakage current and providing DC voltage balancing. The limitations of this method are analyzed and simulations are performed to evaluate its effectiveness. The developed modulation method is also shown to eliminate the low-frequency voltage ripple in the DC bus caused by the conventional modulation methods. An experimental hardware prototype DC-AC converter is designed and built for testing the different modulation methods. Finally, recommendations for future work are made.
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