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.
Highlights
In recent years, there has been an increase in the generation of renewable energy that is asynchronously connected to electric power systems
This study suggests methods for determining time constants so that the minimum frequency that is calculated based on the reduced frequency response (RFR) model is the same as the one that is calculated by the system model that is based on a precise turbine-governor model
This study proposed a method for determining the parameters of the RFR model, which is a single-machine model that considers the nonlinearity due to the restrictions on the generator’s power output in order to apply the methods to inertial constraints in the unit commitment (UC)
Summary
There has been an increase in the generation of renewable energy that is asynchronously connected to electric power systems. In power systems with small inertia and limited PFR capacities, as in an isolated power system, it is necessary to secure additional inertia and primary frequency reserves through existing synchronous generators when there is a possibility of a lack of inertia For this purpose, a unit commitment (UC) must be conducted according to the inertial constraints of the system. This paper presents a method for determining the parameters of a single-machine model that considers the nonlinearity resulting from the restrictions on the generator output, for the inertial constraints in the UC. The proposed single-machine model is a reduced frequency response (RFR) model that uses a simple first-order type turbine-gover of 19 nor model to integrate the governor models of gas and hydropower generators.
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