Grid-Forming Converters: Sufficient Conditions For Rms Modeling

Time-domain simulations are a critical tool for power system operators. Depending on the instability mechanism under consideration and the system characteristics, such as the time constants of controllers, either phasor or Electro-Magnetic Transient (EMT) models should be employed. On the one hand, EMT models provide a detailedmodeling of the system dynamics, thus increase the reliability of stability analysis; on the other hand, using these models increase the computing time of simulations, slowing down the security assessment process. To decrease computational time, system operators could resort to phasor-mode simulations for a subset of disturbances. This paper investigates the appropriateness of phasor-approximation models on simulating events related to power supply and balance stability when grid-forming converters are employed for providing frequency support. Moreover, it provides sufficient conditions and bounds for the control parameters of a grid-forming converter under which the phase-approximation modeling of the component is still valid. The control design is carried out using a simple transfer function approach. Time-domain simulation are performed to validate the transfer function analysis using different control settings and different line impedance characteristics.