Decoupled PQ Grid-Forming Control With Tunable Converter Frequency Behavior

Grid-forming (GFM) converters are a widely-accepted solution for the challenges arising from the decarbonisation of electrical power systems. Ideally, a GFM converter should act as a slow-varying voltage source behind a (tunable) RL impedance to guarantee setpoint tracking and grid support. However, the inherent coupling between active and reactive power greatly limits the selection of the impedance's parameters often leading to the need for additional controllers, for example to provide damping at the synchronous-frequency resonance. This paper proposes a decoupled power controller that combines a complex-power control loop with a virtual admittance to provide freely tunable parameters that provide damping at subsynchronous and synchronous frequency, decoupling of active and reactive power, as well as providing desired behavior over a wide range of frequency. The controller's performance is evaluated and compared to a conventional control approach both analytically and in a laboratory environment.