Distribution Management System Coordination for the Optimal Operation of Medium and Low Voltage Distribution Networks

The worldwide impulse to the integration in the power system of a massive amount of Renewable Energy Sources (RES) for carbon neutrality, supported by new technologies (e.g., energy storage systems, fast communication, smart meters, etc.) are making flexibility not only a need but also a real opportunity to be explored in distribution system planning and operation. This is particularly true if high power – highly coincident demand (e.g., electric vehicle charging stations, heat pumps, induction cooking) and RES have to be accommodated on the system. Unfortunately, the distribution system was designed with minimum observability and controllability, privileging economy and simplicity of operation. Thus, Distribution System Operators are experiencing and facing issues caused by network exploitation non-coherent with the original design assumption (e.g., excessive voltage rises, sudden voltage variations, power congestions, reverse power flow on primary and secondary substation transformers, etc.), that, without resorting to expensive reinforcements, can be solved only with new flexibility services potentially provided by the increasing number of distributed energy resources hosted by their networks. Since many flexibility resources are connected to the low voltage (LV) system (e.g., small photovoltaic plants with and without batteries, customers qualified to potentially participate in demand response programs, slow EV charging points), both medium voltage (MV) and LV networks have to be jointly analysed to account for their mutual interactions. Although the simultaneous analysis of a detailed representation of both systems would be the better solution for optimally operating the networks, it may produce excessive computational burden drawback. For this reason, this paper proposes a procedure for coordinating the distribution management systems (DMSs) of the two voltage level networks. Such coordination, designed for MV and LV networks managed by the same DSO, attributes to the MV DMS the role of master in a hierarchical control that iteratively calls the LV DMS optimisation results. The approach applied to a representative case study demonstrates the opportunity of the involvement of the LV resources in the active management of the network.