Frequency analysis of droop-controlled grid-forming inverter: introducing a current feed-forward control

The loss of inertia in the electrical energy supply network due to the shutdown of conventional power plants has to be replaced by control strategies of renewable energy converters. There are several control approaches of converters to emulate inertia as known from e.g. synchronous machines, such as the virtual synchronous machine (VSM) or the droop control. Even though they should behave similar to synchronous machines in theory, this paper shows which boundaries exist for these control strategies and how they can be modified to obtain the desired behaviour. To investigate the dynamic behaviour of a renewable energy source, a droop-controlled converter is operated in parallel with a synchronous machine as external grid. It is tested for different scenarios such as a load step and short circuit to obtain insights to the fast frequency response, which are then compared with a modified droop control.