Low voltage direct current (LVDC) networks used as electricity distribution systems for a community have the potential of operating at higher efficiencies and can integrate various distributed renewable energy sources and storage elements. However, their emergence is being hindered due to the lack of reliable fault protection techniques. DC faults exhibit extremely fast current rise rates as compared to faults in AC grids. Therefore, this research focuses on developing a fast fault detection and isolation technique applicable especially in LVDC networks. Fault isolation was achieved via solid state circuit breakers (SSCB) due to their fast functioning capability and high controllability levels. For quick fault detection two distinct techniques were selected. The first measured the distribution line’s rate of change of current while the second technique determined the current magnitude by measuring the on-state voltage across the SSCB’s semiconductor device. The complete design of the fault detection circuits leading to isolation has been presented in this research work. The performance of both the designed detection circuits and fault isolation via the SSCB have been validated through practical experiments. The results demonstrated that isolation of the fault subsequent to its occurrence is achievable in just a few microseconds. Hence, this implies that the fast rising DC fault currents can be detected and interrupted in adequate time prior to resulting in any hazardous consequences. ... Read more

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. ... Read more