Hierarchical Control in Islanded DC Microgrids with Flexible Structures

Abstract

In this work, we propose a comprehensive three-layered hierarchical control architecture for islanded DC microgrids (DCmG) to achieve a well scheduled and balanced utilization of various resources. Unlike previous contributions, we discuss a top-to-bottom control scheme guaranteeing voltage stability and allowing for generic topologies. Our supervisory control layer comprises a secondary and a tertiary layer and it rests on top of a primary voltage layer. The tertiary layer is governed by an Energy Management System (EMS), which generates optimal power references and decision variables for generation units by solving an MPC problem at every sampling instant. In particular, the generated decision variables take decisions on turning ON/OFF of dispatchable generators, and operation modes of PV generators and batteries. The secondary layer receives power references from the EMS and translates them into appropriate voltage references for the primary layer by solving an optimization problem. We show that a simplified version of the secondary optimization problem is guaranteed to be always feasible. Moreover, since the voltages can only be enforced at the generator nodes, we provide a novel condition to guarantee the uniqueness of the solution for load voltages and power injection of the generation units.