Unbalanced and over current Fault protection in low voltage DC bus micro grid systems

Unlike traditional AC distribution systems, protection has been challenging for DC systems. Multi-terminal DC power systems do not have the years of practical experience and standards that AC power systems have. Also, the current power electronic devices cannot survive or sustain high magnitude faults. Converters will shut down to protect themselves under faulted conditions. This makes locating faults in DC system difficult, and causes the DC bus to de-energize. A fault protection algorithm and method for a low-voltage DC-bus micro grid system is presented in this thesis in order to revolve the above issues. The main goal of the protection method is to detect and isolate faults in the DC system without deenergizing the entire DC bus. In order to achieve this a ring bus was utilized for the main DC bus. The bus was then segmented into individual zones with solid state bi-directional switches used to isolate the zone in the event of a fault. Each zone is monitored and controlled by an individual Intelligent Electrical Device. A grounding resistor was added in order to limit the amount of ground current. The concepts have been verified in MATLAB. KeywordsDC Distribution, Fault Protection, Micro Grids, Power System Protection, Sold State