The increase of renewable energy sources has favored the connection of new non-conventional generation technologies in electrical power systems. Many of these technologies are connected to the network by means of power electronics causing, among other problems, reduction of the inertia constant of the power system, to the detriment of frequency stability. There are different alternatives to improve the inertial response, but an instantaneous power reserve is always needed. The adequate instantaneous power reserve depends on the mix of dispatched generators. Thus, a flexible tool for determining the required instantaneous power reserve for the day-ahead operation is developed in this work. Obtained results show that the developed tool calculates the required power reserve with great accuracy and speed. Therefore, it serves as support for decision-making regarding instantaneous power reserve dispatch.

Frequency stability analysis of large power systems are extremely time consuming, laborious and may even exceed the computational capacity of modern computers. Hence, simplified power system models have being developed in the literature. These models are usually called System Frequency Response (SFR). In SFR models, generators are represented by transfer functions, nonlinearities are generally neglected and the grid is not taken into account. Conventional SFR models only contemplate the mechanical behavior of speed governors, turbines and synchronous machines of generators. This is because, a common simplification is to consider that frequency and voltage can be controlled independently. However, it is demonstrated that there is an interaction between them, so frequency can be affected by the effect of power system stabilizers (PSSs) over excitation system controllers. In this work, a modified SFR model is proposed, considering the influence of generators excitation control on frequency. Simulation results show an improvement of the accuracy in the estimation of frequency response of the power system.

Instantaneous power contribution is an intrinsic behavior of conventional Electrical Power Systems (EPS). Immediately after a disturbance, whole set of generators and motors deliver their kinetic energy stored in their rotating masses (inertial response). However, incorporation of distributed generation imposes new challenges related to reliability and stability of EPS. Replacement of conventional generators by those connected by power electronics leads to a decrease of system's rotational inertia. Reduction of the Inertia Constant (IC) mainly influences on frequency stability, resulting in faster and less damped frequency deviations than in conventional networks that could lead to EPS collapse. One way to counteract this issue is by providing virtual inertia controlling the DC / AC converters of the non-conventional generators. For covering the initial lack of power it is necessary to provide an instantaneous power reserve, generally coming from Energy Storage Systems (ESS). For dimensioning both, the power reserve and the ESS capacity, it is essential to know the system's IC and estimate how much additional inertia should be provided to prevent the system from collapsing in the face of future contingencies. This paper reviews different existing methodologies for estimation of IC of electrical networks, studying their characteristics and accuracy of their results. This analysis is aimed at having the bases to establish a methodology for sizing the necessary power reserve.