The progressive inclusion of Renewable Energy Sources (RES) in power grids is causing a reduction of the overall system inertia, leading to a reduction of the system resiliency. A possible solution is equipping RES with synthetic inertia controllers so that additional power can be provided in case of severe frequency transients. This work reports the results of a research activity that aimed at improving the maturity of synthetic inertia controllers for wind turbine generators through the design and implementation of a controller prototype based on an advanced version of a synthetic inertia controller. Hardware-in-the-loop simulations are performed to validate the correct behavior of the prototype.