Content for  TS 22.104  Word version:  19.1.0

The energy sector is currently subject to a fundamental change, which is caused by the evolution towards renewable energy, i.e. an increasing number of power plants based on solar and wind power. These changes lead to bi-directional electricity flows and increased dynamics of the power system. New sensors and actuators are being deployed in the power system to efficiently monitor and control the volatile conditions of the grid, requiring real-time information exchange [11]  [12]. The emerging electric-power distribution grid is also referred to as Smart Grid. The smartness enhances insight into both the grid as a power network and the grid as a system of systems. Enhanced insight improves controllability and predictability, both of which drive improved operation and economic performance and both of which are prerequisites for the sustainable and scalable integration of renewables into the grid and the potential transition to new grid architectures. Smart Grid benefits spread across a broad spectrum but generally include improvements in: power reliability and quality; grid resiliency; power usage optimisation; operational insights; renewable integration; insight into energy usage; and safety and security. Overviews of (future) electric-power distribution can be found elsewhere in the literature [13]  [14].

Primary frequency control is among the most challenging and demanding control applications in the utility sector. A primary frequency control system is responsible for controlling the energy supply injected and withheld to ensure that the frequency is not deviating more than 0.02 % from the nominal value (e.g., 50 Hz in Europe). Frequency control is based on having sensors for measuring the features in all parts of the network at all points where energy generation or storage units are connected to the grid. At these points, electronic power converters, also known as inverters, are equipped with communication units to send measurement values to other points in the grid such as a frequency control unit, or receive control commands to inject more, or less, energy into the local network. With the widespread deployment of local generation units, i.e. solar power units, or wind turbines, hundreds of thousands of such units, and their inverters, may have to be connected in a larger power distribution network. Primary frequency control is carried out in one of three ways:

1. Centralised control, all data analysis and corrective actions are determined by a central frequency control unit.
2. Decentralised control, the automatic routine frequency control is performed by the individual local inverter based on local frequency values. Statistics and other information is communicated to the central frequency control unit.
3. Distributed control, the automatic routine frequency control is performed by the individual local inverter based on local and neighbouring frequency values. Statistics and other information are communicated to the central frequency control unit.

  Periodic communication service supporting message exchange for primary frequency control.

In the evolution towards 100 % renewable electric power production, the objective of voltage control is to balance the voltage in future low voltage distribution grids connecting local loads and prosumers, as well as energy storage facilities. The aim is to stabilise the voltage as locally as possible, so that decisions and control commands can be issued as quickly as possible. Distributed voltage control is a challenging and demanding control application. Consumer devices rely on having stable voltage levels to operate successfully. When future energy networks rely on thousands of local energy generation units relying mostly on solar and wind power, then it is crucial to stabilise the voltage levels in all segments of the distribution grid. Inverters, or electronic power converters, measure the voltage and power and change the amount of power injected into the grid, and they connect and disconnect end points from the distribution network. Distributed control means that the automated voltage control shall be performed by the local voltage control units based on local and neighbouring voltage and impedance values. Statistics and other information shall be communicated to the central distribution management system, though.

  Periodic communication service supporting message exchange for distributed voltage control.