A Microgrid Multilayer Control Concept for Optimal Power Scheduling and Voltage Control

In this paper, a novel multilayer control structure for microgrids is proposed. A scheduling layer comprehends the minimization of the microgrid operating costs together with the CO2 emissions produced and provides a sequence of power references for the next 24 h. Subsequently, within the executive layer, an off line ac power flow calculation will be performed to obtain the initial values of the voltage magnitudes of the different microgrid buses. The adjustment layer, which is the scope of this paper, includes a control strategy to maintain the voltage in the network. The purpose of this third layer is to keep the voltage within a pre-specified tolerance band by adjusting the power provided by the microgrid distributed energy resources (DER). Depending on the voltage deviation, the location of the DER units in the network and their distance from the voltage deviation, an appropriate dynamic gain will be provided to the relevant DER units. The renewed settings are then fed back to the first layer, which performs a new optimization and redistributes the adjusted reference set points among the DER units. The performance and effectiveness of the proposed hierarchical multilayer control structure were evaluated and demonstrated by several case studies.