1 Department of Electrical Engineering, Technical University of Denmark2 Center for Electric Power and Energy, Department of Electrical Engineering, Technical University of Denmark
In many countries in the EU and in the United States, coil and nuclear plants provide the majority of energy production [2, 3], while peak absorption is matched by regulation plants and power exchange between grids. Throughout the last two decades, factors, such as increased global energy demand, speculation of fossil fuels, and global warming have generated a high interest in renewable energy sources. Nevertheless, energy sources, such as wind and solar power, have an intrinsic variability that can seriously affect the power grid stability if they account for a high percentage of the total generation. To face these challenges, the scientific community, as well as many industrial sectors, are taking steps to upgrade electrical network infrastructures and related technologies to ensure energy production and deliverance through the next century. The Smart Grid is a new paradigm for electric energy systems, which can intelligently integrate the actions of such actors as: generators, consumers and those that do both, in order to efficiently deliver sustainable, economic and secure electricity supplies . Such scenario requires from consumers (and also producers) a certain flexibility, referred as the capability of a device or cluster of devices to change the power consumption or production in time and magnitude. This behavior can be granted by local controllers or supervisory controllers who are able to operate under the direct or indirect control paradigm . Typical devices that offer flexibility are thermal and electrical storages, whose internal temperature or state of charge (SOC) is to be kept within specific comfort bounds. Alternatively, also PV plants can offer flexibility as soon as the controlling inverters are capable of controlling the power output.