Impact of frequency estimation for VSC-based devices with primary frequency control

This paper presents a comparison of the performance of frequency control devices considering different techniques to estimate the frequency deviation signal. We consider three estimation techniques, namely the center of inertia (COI), the frequency divider (FD) formula, and the phase-locked loop (PLL). The first two are based on the measurement of synchronous machine rotor angles and are virtually exact measures, while the latter is based on an electronic device and is affected by noise and numerical errors. The goal of the paper is first to define whether the PLL estimation is closer to the COI or to the FD. Then, the dynamic response of VSC-based wind power plants and energy storage systems providing primary frequency regulation is studied and compared using the three aforementioned signals. A comprehensive set of scenarios based on the WSCC 9-bus test system is presented in the case study.