## 4 RESOLVD Solution for Smart Grids  
Renewable penetration leveled by Efficient Low-Voltage Distribution grids (RE-SOLVD) is a low/medium Technology Readiness Level (TRL) project, funded under the European Union's Horizon 2020 scheme. The project has developed a complete solution to support DSOs to improve the efficiency and hosting capacity of distribution networks in a context of highly distributed renewable generation, by introducing flexibility and control into the low voltage grid [33]. The overall project's cognitive process can be understood from all the technologies functioning in an integrated way to improve LV grid performance. Phasor measurement units (PMU) and smart gateways measure power-related attributes to instantiate real-time grid observability. In the project, these elements were installed at key locations between primary and secondary substations of the distribution grid. All the data from the PMU andsmart gateways, together with the smart meters, went to a low-voltage distribution decision support tool (LVD-DST), which then provided actionable insights to the grid operator. The LVD-DST could also control certain grid elements directly to perform needed actions in an automated manner. A power electronic device (PED), developed in the project, is a grid element which gets signals from the LVD-DST to provide required grid services through multiple storage devices. The PED comprises of hardware and software components connecting multiple storage devices, and it contributed to achieving most of the value propositions (described later in this section). Through PED, it was also possible to isolate certain sections of the grid and operate them in an island mode. All of the new monitoring and control elements were integrated into a legacy system using a customized enterprise service bus (ESB) and data management platform. In addition to these technologies, a risk-based threat-modeling approach for smart grid technologies has been developed to ensure cybersecurity. Figure 3 shows the different layers of the DSO operation where the RESOLVD technologies fit. The technologies in more detail are:  
* Low-voltage distribution decision support tool (LVD-DST): A suite of web services that provides enhanced energy monitoring and scheduling capabilities. It has three key functionalities: (1) Demand and generation forecasting: uses smart meter data for day-ahead forecasts and prediction of congestion and voltage problems. (2) Fault detection and isolation provides enhanced monitoring of the grid based on multivariate statistics to automatically detect faults and other abnormalities in a statistical sense. (3) Optimal grid operation scheduling calculates the optimal grid operation schedules of active elements (switchgear/storage) in the grid to prevent critical events, reduce energy exchange at substation level and peak shaving. * Power electronics device (PED): This is an innovative power electronics cabinet that permits the integration and synergistic exploitation of various battery types. In the H2020 RESOLVD project, the PED integrated a lead-acid battery pack and a lithium-ion one. The PED was operated so that the main performance of each battery type could be maximized, i.e., the relatively low degradation of the lithium-ion battery in comparison to the lead-acid one under stringent power requirements and the possibility of allocating part of the total required energy storage capability to a low-cost lead-acid battery, thus reducing the cost of the overall solution. The PED was  
Figure 3: The H2020 RESOLVD solution comprised of technologies falling under four layer of DSO operation, as shown in the figure. connected to the LV side of a transformer of a secondary substation in a rural area, which served as the pilot location for the H2020 RESOLVD project.