Research on ULFS Strategies with DGs in Isolated Distribution Systems

Under frequency load shedding (ULFS) is not a new problem. However, the wide penetration of distributed generators (DGs) in power systems especially in distribution systems, may result in new features into this traditional problem. DGs have extensive impacts on power system planning, operation and market management. Hence, it is necessary to examine the appropriate ULFS strategy for a power system especially a distribution system with DGs. On the other hand, one of the strong benefits of DGs is the ability to improve reliability by continuing operation of electrical islands when an event causes the separation from the main grid, hence the wide employment of DGs is helpful for the secure operation a microgrid. Given this background, research on ULFS Strategies with DGs in isolated distribution systems was firstly present to examine different dynamic responses in the microgrid subject to a disturbance. Secondly, with the effects of the developed UFLS strategy, many simulations for different scenarios in a microgrid with DGs ( i.e. a thermal unit and a wind unit) respectively, were carried out. Finally, conclusions on ULFS strategies with DGs in isolated distribution systems was present. It appears necessary to examine the ULFS strategy in an isolated distribution system/microgrid.