Linearized Frequency Deviation Based Frequency-Constrained Unit Commitment with Support from Wind Farm

Abstract

The frequency security is being challenged with the increase of renewable power penetration in the power system. The frequency response equation (FRE) of the system is a high-order differential equation about frequency deviation $(\Delta f)$, which makes it hard to obtain the analytical expression of $\Delta f$. This paper proposes a frequency-constrained unit commitment (FSC-UC) considering frequency support from wind farms. The maximum rate of change of frequency (RoCoF) constraint and quasi-steady-state (QSS) frequency constraint are derived based on the average system frequency (ASF) model. The sufficient condition of frequency nadir constraint is analytically derived with a linearized $\Delta f$ method, which takes into account that the system inertia changes with the combination of online units. The comparison between conventional unit commitment (C-UC) and FSC-UC demonstrates that the proposed FSC-UC can schedule sufficient system inertia and primary frequency response (PFR) resources to ensure the security of system frequency.