Technical and Economic Impact of the Inertia Constraints on Power Plant Unit Commitment

Abstract

The whole interconnected European network is involved in the energy transition towards power systems based on renewable power electronics interfaced generation. In this context, the major concerns for both network planning and operation are the inertia reduction and the frequency control due to the progressive decommissioning of thermal power plants with synchronous generators. This paper investigates the impact of different frequency control constraints on the unit commitment of power plants resulting from market simulations. The market outputs are compared in terms of system costs, and of frequency stability performance evaluated on the basis of the rate of change of frequency and the maximum frequency excursion. The best compromise solution is found using a multiple-criteria decision analysis method, depending on the choice of the decision maker's weighting factors. The proposed approach is tested on a real case taken from one of the most relevant future scenarios of the Italian transmission system operator. The results show how the best compromise solution that can be found depends on the decision maker preference towards cost-based or frequency stability-based criteria. Index Terms-frequency stability, inertia constraints, multiple-criteria decision analysis, power system inertia, rate of change of frequency, unit commitment.

Modeling of Linearized Generator Inertia Constraints for Unit Commitment

“…As the inertia of the power system decreases, frequency changes in response to supply and demand imbalances increase in intensity, and thus, maintaining the frequency stability of the system is challenging [2]. Currently, the inertia of power systems is gradually decreasing with the rising share of power supplied from asynchronous sources, such as wind or solar power [3][4][5][6][7][8][9]. To maintain frequency stability in these power systems, sufficient system inertia and primary frequency response (PFR) must be ensured.…”

“…In this regard, studies have explored methods to secure the system inertia directly through synchronous condensers or to support the system inertia through power electronics such as the battery energy storage system [6,10]; however, the system inertia is fundamentally secured through synchronous generators. Thus, to maintain frequency stability, methods are needed to secure the system inertia in the unit commitment (UC) [9][10][11].…”

A feasibility study of using MV and LV distributed energy resources flexibility in a TSO/DSO coordination perspective: the case study of Milan, Italy

“…Given the DERs priority in the future energy system, operational actions must be optimized to support the necessary market framework while maximizing costefficiency and supply security [18][19] [20][21] [22]. As an increasing share of generation connects to DSO grids, in particular, the majority of RES is connected at low and medium voltage levels, one of the most operational challenges for TSOs is maintaining overall system security.…”

Multi-area Frequency-constrained Unit Commitment for Power Systems with High Penetration of Renewable Energy Sources and Induction Machine Load

“…Considering the highly nonlinear calculations of frequency security indices of power systems, the FCUC is mostly modeled with mixed-integer nonlinear programming (MINLP), which cannot be solved efficiently by commercial solvers. In [9] and [10], the complicated frequency index constraints are substituted with constraints, such as inertia, kinetic energy, and available synchronous capacity. These constraints can be represented in a simple form.…”