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This paper describes an enhanced droop-based grid forming control method for inverter based distributed energy resources. The important advantage of inverter control over traditional synchronous machine behavior in terms of independent control of frequency and phase is highlighted. This degree of freedom is used to give the inverter control an inherent damped reaction to grid events, like voltage jumps, frequency or phase changes. The control is analyzed in the state space for three essential applications, i.e. grid parallel operation, two weak coupled power resources and two area system with two resources per area. It is shown, that the suitable damping coefficient mainly depends on the parameters of the power resource itself, like short circuit impedance and filter time constants, and is fairly independent on the residual system parameters. Simulation results confirm the analytical design of the damping coefficient. Experimental results gained in a complex power system laboratory validate the behavior for typical grid events.
Klaes et al. (Mon,) studied this question.