Single-Machine Frequency Model and Parameter Identification for Inertial Constraints in Unit Commitment

Abstract

In recent years, the need for generation mixes that consider the inertial constraints in unit commitment (UC) has increased because the inertia of these systems has decreased with the increased use of renewable energy. In these circumstances, single-machine models can calculate the minimum frequency and rate of change of frequency (RoCoF) at a high speed in terms of the characteristics of the changes in the generation mix, in order to identify the generation mixes that can satisfy inertial constraints. This study proposed methods to determine the parameters of the reduced frequency response (RFR) model, which is a single-machine model that considers the nonlinearity caused by restrictions on the generator’s output power, in order to apply inertial constraints to UC. The RFR models can include various forms of governor models and consider the nonlinear response characteristics of restrictions on the generator’s output power that change according to the scales of contingencies, system inertia, and changes in load characteristics through these parameters. From the simulations of real systems, it was observed that the parameters determined through the proposed methods achieved considerable accuracy in calculating the minimum frequency and RoCoF with the RFR model.

Modeling of Linearized Generator Inertia Constraints for Unit Commitment

“…This model, which is based on the basic concept of the swing equation, estimates the frequency of the system in response to power imbalances [26,27]. The RFR model uses the equivalent turbine-governor model as a general and simple first-order system and is illustrated in Figure 1 [28].…”

“…This model, which is based on the basic concept of the swing equation, estimates the frequency of the system in response to power imbalances [26,27]. The RFR model uses the equivalent turbine-governor model as a general and simple first-order system and is illustrated in Figure 1 [28]. Studies on inertia constraints have mainly used system frequency response (SFR) models [29,30] based on reheat steam turbines [20,22,24,25].…”

“…is as follows [28]: Studies on inertia constraints have mainly used system frequency response (SFR) models [29,30] based on reheat steam turbines [20,22,24,25]. The RFR model is advantageous as it can cover a wide range of generator types; this benefit is attributed to the usage of a simple turbine-governor model.…”

“…For the system presented in Figure 1, when the damping ratio ζ is in the range 0 < ζ < 1, the analytical expression of the frequency deviation ∆ω(t) is as follows [28]:…”

“…The analytical expression for the minimum frequency deviation ∆ω(t min ) in the RFR model is as follows [28]:…”