A paradigm shift from Grid Following (GFL) to Grid Forming (GFM) converter control has been proposed by some transmission system operators (TSO) to address challenges around fast inertial response, not least during severe contingencies, and other stability problems that are observed in power systems with few remaining synchronous generators and large long-distance power flows. In Europe, requirements for GFM controls for Power Plant Modules (PPMs) are under consideration for upcoming European regulations (RfG 2.0, NC HVDC 2.0) and have been included as additional requirements in the German grid code for HVDC-connected PPMs, and as an optional service in the UK grid code.

Compared to GFL controls, GFM converter controls deviate more from a converter’s power setpoint , due to the dynamic reaction of the controls to, e.g. voltage phase jumps, frequency gradients and voltage events. In wind turbine generators (WTG), this introduces a stronger coupling between grid events and the mechanical system, which had previously been overcome in full-converter turbines. Implementation of GFM on WTGs therefore faces several obstacles that make the application of this control concept challenging:

- WTG converters are not designed with electrical energy storage and must satisfy active power requests by corresponding active power changes on the machine-side converter, and therefor onto the mechanical WTG components

- The only inherent energy storage of a WTG is the energy stored in its rotating masses.

- Access to this energy is limited by the dynamic limitations of WTG’s, e.g. on the rotor speed, as well as load limitations of drivetrain, bearings, and other mechanical structures.

A concept study is presented in this paper showing how GFM controls may be implemented on a WTG PPM while respecting the above limitations and also providing key GFM control functions, including the following:

- Instantaneous reserve / inertia power provision.

- Dynamic voltage control without reactive current specification / fast reactive power response.

- Temporary islanding of a High-Voltage Direct Current (HVDC)-connected PPM in case of blocking of the HVDC converter.

Electro-magnetic transient simulation results and full-scale converter test rig results are provided to illustrate the concept study.