In smart grids, grid inertia (typically provided by gas/steam turbine based synchronous generators) is a very important measure of power networks' stability. Low grid inertia will make power networks suffer from poor power quality and increased risk of blackouts. Massive offshore wind turbines however don't provide grid inertia due to the use of frequency converters between wind turbines and power networks. This becomes one of the most challenging barriers for integrating more offshore wind energy sources into power networks in the research field of smart grids. There are some existing works aiming for creating virtual grid inertia by using control strategies and wind turbine models. But these works didn't study virtual-physical systems' coupling/twinning, thus couldn't guarantee the convergence and the synchronisation of virtual and physical systems. Digital twin technologies aim to solve these problems by using seamless and real-time connections for enabling real-time data flow from physical systems to virtual models, and information flow from virtual models to physical systems, thus tightly twinning virtual and physical systems. This project aims to develop digital twin technologies for better coordinating wind turbines and energy storage units to provide virtual grid inertia, thus facilitating greater penetration of offshore wind in power networks.