LVDC Distribution systems are becoming popular due to the avenue of integrating renewable energy sources on a large scale. Predominant DC based power system architecture has been predicted to serve the needs of a sustainable society that holds the capability to self-generate, share, and trade power produced from renewable energy sources. Bottom - up approach beginning from development of products that run on DC till microgrids and integration of rural communities using LVDC distribution presents as a promising avenue for adoption of DC grids worldwide. Many areas in DC distribution system are yet to undergo rigorous study both theoretically and practically. Touch protection is one such area which is largely unexplored. Residual current devices (RCD) are traditionally implemented at the load side to trip at specific residual current levels ranging from few to hundreds of milli amperes. Current trip thresholds and time within which the fault must be isolated are different for DC. There is dearth of standards for DC RCD. In this thesis project we attempt to design a compact, reliable, and cost-effective RCD. The designed and developed prototype is tested at DC Low Voltage levels for various residual current magnitudes to determine important parameters like reaction time and accuracy.

An isolated bidirectional DC-DC converter is designed for a dual-output EV charger. Various DC-DC converter topologies are compared, including single-output converters and dual-output converters. Then one suitable topology is selected between the multiport CLLC converter and triple active bridge converter based on the simulation performances for the dual-output EV charger. Meanwhile, an investigation into the voltage regulation for a wide output voltage range is conducted with the research of interleaved buck converters. Finally, the system-level control of the EV charger is designed for different operation modes and the converter is modelled in PLEVS and simulated under different scenarios.

The use of DC microgrids in combination with photovoltaic (PV) energy generation sources results in higher efficiencies by avoiding AC to DC conversion. Moreover, bipolar DC grids allow for more system flexibility and increased reliability at the cost of an additional conductor when compared to unipolar DC. However, maximum power point tracking (MPPT) converters are still required in order to optimize the power delivered to the microgrid by PV systems. The development of more efficient and cost-effective DC-DC MPPT converters will be proven vital considering the expected growth in solar PV installation as a consequence of the relentlessly increasing global energy demand.

The objective of this thesis is to design a DC-DC MPPT converter for bipolar DC microgrids based on gallium nitride (GaN) high-electron-mobility transistors (HEMTs). GaN transistors are wide-bandgap semiconductor devices that can operate at very high switching frequencies due to their superior electron mobility compared to other semiconductor materials used in electronic switching. Increasing the operational frequency of an electronic converter allows for smaller passive components, which in turn has the potential to result in system size and cost reductions. A complete electrical and thermal analysis of the performance of these components is simulated and presented in this report, and the implications of employing these devices for the selected application are evaluated. The design overview of the DC-DC MPPT converter using these GaN HEMTs is also showcased in this work, as well as the results obtained from testing the assembled DC-DC MPPT converter for bipolar DC microgrids. The main conclusions of this work aim to clarify the advantages of GaN devices in MPPT applications, as well as demonstrate a design solution to the integration of MPPT converters to DC microgrids. The project was developed in collaboration with the company DC Opportunities, and the designed converter was assembled and tested in their laboratory.

Rural electrification remains a significant challenge for engineers, given its intricate relationship with multiple issues, including geographical constraints and underdeveloped infrastructural provisions. As a result, with the development of Solar Home Systems (SHS) and direct current (DC) microgrids, DC systems for energy access have emerged as a promising solution.

In this context, a bidirectional DC/DC converter serves as a bridge connecting the SHS and the grid. Thus, it is important to design a converter's control mechanism to ensure a smooth and efficient exchange of power in both directions. Beyond this aspect, the system perspective involves the coordination of photovoltaic (PV), battery storage, and grid power supply priorities within the SHS. Consequently, this thesis centers its attention on two objectives: the control of the bidirectional DC/DC converter and the system-level control of the DC microgrid.

To ensure high efficiency under variable loads and smooth transitions between two directional operations, this thesis proposes and evaluates a novel control methodology. Transfer functions are derived through mathematical modeling and PI parameters are determined by analyzing Bode-Plots. This work also shows the simulation and testing results. Both results demonstrate that the proposed control method achieves a high efficiency under light load conditions, maintaining a stable output voltage despite load power dramatic fluctuations.

Analysis of energy exchange between the DC microgrid and SHS involves a bipolar DC microgrid model based on an established grid in Matlab/Simulink. Employing droop control, which is a widely used decentralized strategy, for each converter within the grid. To ensure priority order of power supply in the system, a system-level decentralized control methodology is developed, assuming internal communication within the SHS. Through simulation, the priority order of PV, battery, and grid is verified, along with the impact of dynamic shifts between scenarios on the load. However, given the absence of communication devices in the existing SHS, an alternate decentralized coordinated control strategy is developed and simulated, without direct communication interfaces. Simulation results demonstrate that the SHS bus voltage remains stable even with power supply changes.

Recently, there have been numerous DC microgrids coming up in every sector. Some of these microgrids operate as independent entities with their own renewable energy sources, active loads, distribution networks and energy storage units. However, they are not highly reliable as the renewable energy sources are location and climate dependent. Having a large energy storage unit can be one possible solution, but that involves high expenditure and occupies a large amount of space. Thus, an alternative is to connect the independent DC microgrid to an established AC grid. With the advancements in power electronic technologies, such a connection can be established by a multi-stage converter known as Solid state transformer (SST).

Numerous studies have been conducted on SSTs for low-voltage levels, and there is a wide scope for research in the area of medium and high-voltage converters. Also, the scope of using Planar transformer (PT) as high-frequency transformers in DC-DC converters for medium and high-voltage applications is yet to be extensively explored. Hence, the main focus of this thesis would be to develop an isolated bidirectional DC-DC converter with a planar transformer that can be used in an SST which can potentially connect a low-voltage DC microgrid comprising a solar-based car parking system, to a medium-voltage AC grid.

Firstly, various DC-DC converter topologies have been investigated, and the single phase Dual active full bridge (DAFB) is chosen as the best suitable topology for this application. Secondly, various control strategies have been investigated, and single-phase shift control has been implemented due to its simple control techniques and low data transfer requirement across high isolation. Thereafter, a script is developed to identify the optimal parameters for the Dual active bridge (DAB) and PT design. Further, the planar transformer with high isolation is realized by considering various factors like shielding and termination into account. Finally, a single-cell prototype is developed and tested for DAB operation and isolation requirement of the designed planar transformer.

The result of the presented work is a single-cell isolated bidirectional DC-DC converter rated for 12 kW designed and developed with a PT rated for 16.3 kV isolation.

To tackle the effect of climate change while meeting the ever-growing demand of energy, a high scale of integration of renewable energy resources has been performed in the past decade. Solar Photovoltaics have played a monumental role in this process, thus contributing in the fulfillment of the energy demand. The scalability and the flexibility of use has led to a significant development in the technologies implemented for assimilation of Solar PV. In addition, the development in power electronics has made the process of integration seamless. Due to Solar PV's dependency on irradiation there is an ever growing need for establishment of an improved control on power converters.
The aim of this thesis is to implement Maximum Power Point Tracking and Droop control algorithms on PV powered DC-DC Converters while considering the dynamics of Solar PV. Mathematical modelling is used to model the PV generator to consider its dynamics along with the dynamics of the converters to establish control. The output of these converters is connected to a DC Microgrid. After completion of the modelling process, the internal control design was performed followed by the implementation of both the algorithms. The project was performed at the lab of the company DC-Opportunities.
The findings of this research are presented in the current document. Its goal is to outline the procedure taken from the start of the project and the literature review all the way through the design and testing of the power electronic converters. Finally, suggestions for the future are offered, which might serve as a roadmap for more advancements.

The increasing penetration of the distributed energy sources and the increasing load on the AC grid demands for integration of DC grids in AC distribution network. This has resulted in the requirement of power electronic converters such as DC/AC converters. For different operating conditions of the DC/AC converter it is not recommended for the converter to operate in open loop. Hence, while designing the control for the converter there are challenges such as the presence of unbalance on the grid leading to higher losses, offsetting of AC voltages at the output and grounding of the converter leading to higher common mode voltage and currents. This thesis explores the control strategy that can be implemented on the converter to mitigate the unbalance in different operating conditions and compares different modulation techniques to reduce the common mode voltage and currents.
To begin with the islanded operation is considered for the converter and the voltage control is implemented on this type of converter. Further a modification on this type of control is proposed for the operation of converter under overcurrent scenario. Subsequently the control strategy for grid connected operation is analyzed such that the issue of unbalanced currents on the grid is mitigated. Three different operating modes are considered under grid connected operation for validating the control strategy proposed. Following the controlled operation in islanded and grid connected scenario, the active methods for reducing the common mode voltage are reviewed by comparing different modulation techniques.
On the discussed control strategies for different operating conditions of the DC/AC converters, an optimized implementation of the control on the microcontroller is presented. Other functionalities such as protection of the converter against unwanted actions is investigated through implementation of state machine. The results of the controlled DC/AC converter operating in islanded operation is presented and modifications in the existing PCB are discussed to make it compatible to operate under grid connected condition. The operation of control strategies implemented is validated for the real time application of the converter with unbalanced load conditions.

The DC Optimal Power Flow (DC-OPF) problem is a widely-studied topic in the field of power systems. A solution to the problem consists of minimizing the running costs of the power system, through defining the optimal operating state for each entity in the system, while adhering to a set of physical constraints. A lot of research has been conducted on decentralized and distributed solutions to this problem, which, when compared to centralized solutions, offer benefits such as adaptability, reliability and scalability. Nevertheless, most of these solutions have only been evaluated through simulations, while physical applications of these algorithms introduce new challenges, such as noise, delays, and the regulation of physical variables like voltage and current. In this thesis, we focus on a decentralized DC-OPF algorithm based on the Consensus and Innovation method, where system entities utilize their physical measurements and communicate with their neighbouring entities in order to reach consensus on a solution. While previous implementations of the algorithm were tested on simulated environments, this thesis explores and proves the effectiveness of the algorithm implemented for a real DC unipolar microgrid, consisting of power supplies, loads and a Power Circuit Board attached to each, where each device's behavior is governed by its own, exclusive entity. The newly-introduced challenges of a physical environment are accounted for, and any negative effects of them are mitigated as much as possible. Furthermore, the algorithm is successfully modified and extended to handle region DC-OPF, something that has not been attempted before, where a single entity of the algorithm could be responsible for many devices in the network. Finally, it is known that the original algorithm has not been experimented on before on scenarios of islanding and de-islanding, which are of importance in OPF, because a power fault may occur and one area may wish to isolate itself from the faulty area, or perhaps a distributed energy resource should only be connected to the network during certain periods, e.g., during sunlight for solar panels. Hence, this thesis also proves the effectivess of the algorithm on scenarios of islanding and de-islanding, in an innovation site called the Green Village, where technologies in the field of sustainable energy provision are tested and applied in a real-life environment.

The optimal power flow (OPF) problem is a classic and widely-studied topic in the field of power systems.Its purpose is to minimize the running costs of a power system by determining the optimal operating points,while respecting a set of physical constraints. While most power systems are currently controlled by a centralcoordinator, there is significant interest in the research of decentralized schemes. By eliminating the need fora central coordinator, fully decentralized algorithms eliminate the single point of failure, thereby enhancingthe reliability of the overall system. Moreover, as communication and telemetry play a progressively vital rolein the power grid of the future, decentralized methods reduce the strain on the data infrastructure. In otherwords, the computational and communication load on the central computer is decreased, as it no longer hasto gather and process large amounts of information from all the nodes in the system. As a result, although newchallenges are introduced with distributed algorithms, the OPF becomes more scalable in some regards. Onefully decentralized method for performing OPF calculations is Consensus+Innovation (C+I). The C+I methodis based on the Karush-Kuhn-Tucker (KKT) Conditions class of optimization, where the solution is founditeratively using an update strategy. Moreover, communication is only required between directly connectednodes, or neighbors. This method has been applied in the cases of AC systems as well as unipolar DC systems,reporting promising results. However, until now, no decentralized algorithm existed for bipolar DC systems.Bipolar topologies, while they are more complex to model and optimize, possess numerous advantages overunipolar ones. By providing two voltage levels, larger loads can be connected directly between the two polesin order to provide double the power. This increased voltage level allows for the current to be halved for thesame amount of power, thereby significantly reducing the conductive losses. On the other hand, smaller loadsare connected between one of the poles and the neutral, meaning that power electronic devices with lowerratings can be used. Furthermore, generators and loads can be connected in parallel at the same location.This means that they must be modelled as controlled current sources which are connected between twophysical nodes. In other words, the optimization variables are altered from nodal voltages and powers tonode voltages and source currents. However, these changes in the modelling, optimization, and control of thegrid mean that the single line diagram (SLD) equivalent circuit, used by the algorithms for unipolar systems,is no longer valid for bipolar ones. Thus, the objective of this thesis was to develop a fully decentralized OPFalgorithm for bipolar DC grids. The algorithm is based on online optimization, meaning that measurementsfrom the physical grid are taken and used in every iteration of the OPF. Moreover, the algorithm is based onbipolar DC grids wherein the power electronic converters follow a droop control scheme, the effect of whichis directly accounted for in the newly developed update strategy. The algorithm is tested on four differentsimulated case studies with varying operational scenarios. These test cases include both fixed and variable-power loads and controllable generators. Furthermore, the algorithm is demonstrated to successfully achieveline congestion management using demand response. Finally, a case with unbalanced loading is simulatedsuccessfully, while respecting all of the physical limits of the system.