Three-Phase SRF PLL Model for System Frequency Response Studies in Low-Inertia Systems

This paper derives a small-signal model of a three-phase synchronous reference frame phase-locked loop for use in system frequency response studies assuming a system of balanced three-phase voltages. The small-signal model is described by a second-order transfer function which relates the actual to the estimated grid frequency. The small-signal model behaves identically to the large-signal model for small disturbances. Simulation results demonstrate that phase-locked loop dynamics can be neglected in the high-inertia scenarios, while in the low-inertia scenarios they have a significant impact on the grid frequency and should be included in models.