Virtual Power Plants and Virtual Inertia

Abstract

In a general way, the electrical network is the set of lines, transformers and infrastructures that carry electricity from generation centers to final consumers. The current networks were designed and are in operation since the mid-twentieth century and were conceived to cover a situation in which the main generation centers were far from the populations. The new energy model is totally different and is transforming the current system into a distributed system, in which any agent that is connected to the network has the possibility of providing energy, enabling the creation of microgenerators, so that there is no such direct dependence as with the current energy generation. Thanks to this type of network, it is possible to drastically reduce losses due to energy transport, facilitate the connection to the network of all types of renewable energies and support energy storage capacities. But this structure requires management systems and integration of the microgenerators in the electrical system and it is in this moment when the concept of Virtual Power Plant (VPP) appears, which arises from the grouping of a series of small generators acting as a unit. Taking value from the energy microgeneration concept and the microgrids, a VPP connects many of these microgenerators to work together as a traditional plant through a centralized control system. A VPP achieves to interlink multiple concentrated sources in one area: wind, solar, storage batteries, biomass plants and conventional generation sources, and coordinate them through remote software. A Virtual Power Plant is one of the main functions of the smart grids. Through it, various distributed generation resources are brought together, dispersed throughout the network, with the capacity to respond intelligently to demand control and turn them into positions of active resources that function as a single centralized generating plant. In this way, the capacity of the virtual plant would be the sum of the powers of all the elements that make it up. We can say that VPPs use the Intelligent Network to enter the system and this can represent a reduction in demand and therefore affects the offer. It is called Virtual because it is in the digital world where, through telecommunications and control networks, it can be linked to physical elements through software. For the virtual power plant, sensors are used to collect data that are collected through a secure telecommunications infrastructure to convert them into information and be controlled by the system operator. The VPP is then a technical, operational and economic concept that is located in the digital part of the electrical network and provides facilities that allow greater flexibility of the electrical system. On the other hand, in recent years, within the electrical generation system, wind power has taken on great importance and has significantly increased its share of space in the generation market. This has implied an increasing value in the number of wind turbines connected to the network. This growing penetration of wind generation involves new factors to be taken into account in aspects such as frequency control, where the inertia of the system plays a determining role. The inertia of the system determines how the frequency will vary when a change occurs in the generation or in the power demand. The doubly-fed induction generator wind turbines, the preferred choice for extensive wind farms, can reduce the effective inertia of the system. These variable speed wind turbines can emulate inertia by fast active power control. This virtual inertia can be taken as an important way for the control of the frequency.