Increasing the part of Renewable Energy Sources (RES) in modern power grids is of critical importance for the transformation of the global energy system. However, stability and participation to ancillary services issues related to RES limit their use. Indeed, the RES grid integration faces major limitations when high RE penetration is expected. A solution to overcome this is to increase the share of so-called dispatchable RES, i.e., the ones which have a natural storage capacity. The main objective in the POSYTYF project is to group several RES into a systemic object called Virtual Power Plant (VPP). VPP is a way to aggregate RES sources to form a portfolio of dispatchable/non-dispatchable RES able to optimally internally redispatch resources in case of meteorological and system variations in order to provide sufficient flexibility, reliable power output and grid services. The POSYTYF project will provide TSOs, DSOs and generators with knowledge, models and tools for synthesis of VPP controls both for local (production) and grid (ancillary services) objectives. New analysis (stability assessement) and control (centralized vs decentralized concepts) methods will be particularly proposed. Solutions will be immediately implementable in the actual grid and regulatory situation. Realistic (large-scale grids and concrete RES technologies) cases will be treated and full validations – both in simulation and hardware in the loop along with the codes for regulator’s implementation will be made available. Proposals for some main problems like stability will be formulated for next generation grids of massive RES penetration and low inertia systems. The interdisciplinary and ambitious POSYTYF project brings together 10 partners from 4 EU countries. They will bring the VPP technology from TRL 3-4 to TRL 4-5 by evaluating new stability issues, proposing new control algorithms.