Despite of the technological advancements on renewable energies and integration of those into the grid, there are still around 800 million people who lack access to the electricity. In order to tackle this problem, solar home systems are being deployed especially in rural areas to create units for decentralized energy generation, based on DC microgrid premises. Integration of solar home systems, especially in developing countries, has great positive effects on communities' economic and social conditions.
In line with transition to cleaner energy resources and utilization of these, this thesis has been carried at DC Opportunities RD to facilitate the rural electrification project. Within this project, the thesis focuses on implementation of a general adaptable firmware based on USB Type-C power delivery protocol on several components of modular solar home system.
Firstly, the report analyses the existing solar home systems with their characteristics on power delivery and energy management. The limitations on the existing projects are studied and the main motivation on deploying the firmware is pointed out. The main objective of the thesis is hence is formulated as achieving and implementing the USB Type-C power delivery protocol with data acquisition layer on prototypes of charging station, power banks and charging hub, that is tailored to rural applications. The firmware design topology is followed to take into account the modularity, scalability and applicable to energy management.
The USB Type-C power delivery firmware is developed by studying and adapting two open source packages. Several adaptation layers are developed and the firmware is implemented using micro controllers, from STM32, that are capable of running operating system with no faults, deploying several layers of tasks and state machines. Power delivery library functions are tackled with layers of software architectures and data monitoring and transmission layer is deployed, in order to validate the system as well as the hardware.
Implemented firmware is developed on the prototypes and tests are run with the current editions of the prototype. The energy management layer and formulated test case will be run and tested on March 2020, in the field test in Ethiopia. This field test will provide results and data, thanks to the developed firmware and acquisition system, in order to achieve a step closer to the ultimate goal of the project, which is implementing low voltage DC microgrid in rural areas.

There are many methods for solving an optimal power flow (OPF) problem. Most of them employ one central unit to solve the problem (centralized) while in others, every node/area computes for its coverage and send information to its neighbor(s) every time. The mentioned method is called Distributed OPF. In this thesis, the Distributed OPF aims for a fast and resilient algorithm to solve a DC-OPF problem based on Consensus + Innovation (C+I) method.
The research focuses on developing a faster algorithm in solving an OPF problem for a DC distribution grid. The current C+I method has tuning parameters, all of which are determined by trial and error for every case. They are sensitive parameters that determine the speed of the iteration to converge to the solution. This thesis attempts to form adaptive tuning parameters by understanding their function in every equation for a variable update. By understanding the purpose of each tuning parameter and the physical interpretation, some parameters can be formulated while the other is still determined by estimating the value. The losses and congestion are also taken into account. In the results, by formulating these parameters, they are shown that the iteration number has dropped significantly compared to the previous research.

Regarding the resilience of the algorithm, the distributed approach relies on the information exchange between the nodes and delay on the information exchange will stall the whole iteration process. Therefore, an asynchronous algorithm is implemented to resolve the problem by setting a timeout duration. The timeout duration enables the algorithm to wait for the new information only for the desired duration, and therefore the calculation converges in faster.

Meshed LVDC distribution grid is considered to be more efficient and reliable than AC distribution network.
This applies in particular when there is a significant portion of DC sources, storage, and loads in the grid. Its
optimal operation, however, is not inherent. The power flow in distribution network can suffer from congestion
due to the line impedance of the system. Thus, a device that can regulate the power flow is regarded
important. Several works have proposed DC-DC transformer and series voltage source type of power flow
control device for HVDC application. DC-DC transformer, however, needs to be rated at full grid power.
Meanwhile, series voltage source type for HVDC requires an additional connection to either nearby AC network
or other lines. This thesis presents a function and requirements validation of a novel power flow control
converter (PFCC) which only requires partial power rating with respect to the grid rating, needs no additional
connection to other lines, and can regulate power flow in four V-I quadrants. The proposed topology able
to performs power regulation with a fraction of grid power in all of the quadrants both in simulation and
experiment.

DC Microgrids could play an important role in a renewable and sustainable future. Unfortunately, there are not enough standards or guidelines for the implementation of DC Microgrids or DC distribution grids in general. Nevertheless, reliability and security of such a system must be assured at all times. As a consequence, an important challenge lies in terms of protection.

This thesis project focuses on capacitive grounding and their respective ground fault detection and protection scheme for a general DC distribution grid. The protection scheme proposed aims to discriminate currents caused by load shifts from ground fault currents with as little communication between the protective relays as possible.

The safety requirements needed for a DC distribution system are analyzed and threshold values for current that may endanger the human body are derived from literature. A scheme using capacitive grounding is analyzed further through a sensitivity analysis for capacitor size. This analysis serves as a starting point to determine an important challenge for the discrimination of currents caused by load shifts and human faults. A detection scheme is proposed to differentiate these currents and demonstrated with Matlab Simulink.

An analysis showing the behavior of the system to increasing number of grounding points using this detection scheme is further discussed and studied by means of state space representation. This analysis helps as a starting point for the scalability of DC distribution systems with capacitive grounding.