Frequency Support for Remote Microgrid Systems With Intermittent Distributed Energy Resources—A Two-Level Hierarchical Strategy

A two-level decentralized hierarchical control strategy is developed to cope with active power deficiencies in remote microgrid (MG) systems containing intermittent energy resources. The primary level consists of a multilayer droop-based scheme designed to dispatch the required loads to be shed amongst controllable loads (CLs). The dispatch is proportionally fulfilled through the appropriate assignment of each layer of the droop curves to its corresponding priority type of the CLs. If the primary level is unable to handle the shortfall, the secondary level of the scheme is invoked by coupling of the overloaded MG with a neighboring one. Appropriate criteria are accurately formulated to assure desirable interconnections and proper isolations of the MGs. By detecting an overloading condition, the primary level attempts to raise the frequency by managing the CLs, whereas the secondary level assesses the possibility of forming a system of coupled MGs (CMG). Depending on the level of support provided by the neighboring MG, the shed loads can be restored completely or partially once the system of CMG is formed. Implementation of the two levels is coordinated such that the power shortfall can be relieved with very low bandwidth communication systems. Validity of the proposed strategy is demonstrated through several PSCAD/EMTDC studies.