Evaluation of the influence of equivalent inertia variations on power systems using stochastic simulations

Abstract

It is well-know that several aspects are involved in the changing nature of the energy matrix throughout the world, including environmental concerns and the reduction of costs of new power generation technologies, which explain the push for an increasing usage of renewable energy sources (such as wind and sunlight, for example) to generate electrical power in large-scale systems. On the other hand, challenges are still faced for a massive integration of these power sources into the system. Among them, the one that is addressed in this research project is the reduction of frequency support caused by the inception of these power sources. Since the Rate of Change of Frequency (RoCoF) in a system is dictated by the difference between power generation and consumption, a variation in the consumption must be followed by a proper response by the generation, in such a way that a match between these two is established (after a small variation of the RoCoF during the transient period). For rotating machines directly connected to the system, due to their mechanical inertia, energy can be quickly released from or absorbed by their rotors to counteract the effects of a change in power consumption. On the other hand, some of the fastest growing renewable power sources (particularly wind farms and solar photovoltaic plants) do not behave as previously described, mainly because they are connected to the grid though power electronics devices. This type of connection creates a parcial decoupling of the dynamics of the primary energy source from the ones of the electrical grid, making these sources less sensitive to the RoCoF. This effect is often viewed as a reduction of the equivalent inertia of the system. In this context, the main objective of this project is to investigate the relation between the RoCoF and the equivalent inertia of the system through simulations of the system response to a change in its operating conditions. The focus is on cases where the value of the equivalent inertia is very low and vary in a stochastic manner during the simulation, since this scenario is becoming increasingly probable in practice given the previously established context. The results of the project can shed light on problems already faced by system operators around the world and contribute to the proposal of solutions for these problems, enabling a better use of the potential of the mentioned types of renewable energies for electrical power generation. (AU)