Power System Frequency Domain Characteristics for Inertia Estimation from Ambient PMU Data

Current inertia estimation methods aim at determining a mass or inertia parameter of an underlying power system model by using bus frequency and real power output from PMU time series data. However, this neglects the fact that t inertial response depends of other processes within the grid andhe the power plant control systems. This becomes especially important under the presence of governor dynamics and even more difficult during periods of automatic generation control (AGC) operation. However, due to the turbine governor's time constants being longer, it is hypothesized that the effect of certain low-frequency dynamics can be filtered out of the frequency domain in the ambient data to obtain an inertial response across a specific timescale. An investigation of this hypothesis is presented in this work, aiming to give insight on the frequency range where the filtering can be applied. Furthermore, this work aims to extend the concept of inertia as a constant parameter to a frequency domain inertial response when attempting to estimate the inertia of a power plant. Simulations are performed using a nonlinear model of a single-machine system under ambient load perturbations and comparisons drawn to estimates obtained from an event.