Content for  TR 22.867  Word version:  18.2.0

The SE service relies as input on the information of the electric grid topology, the electric line parameters and the real-time measurements provided by the instrumentation deployed on the field. Given this set of inputs, the SE service processes the received data to provide the most likely operating state of the network at the considered instant of time (the same time at which the measurements are collected). Finally, the results of the SE service are sent to the control centre (or whatever data concentrator) to give situational awareness to the DSO and, if needed, are made available for other control functions requiring this information. SE results are usually also stored in a database for possible a posteriori analysis. For its operation, the SE service thus needs as input some important information of the grid characteristics, the deployed measurement infrastructure, as well as the real-time measurement data collected from the measurement units in the field. In addition, if the electric grid is reconfigurable (i.e. topology changes can be applied), the status of the switches and breakers should be also provided in input to the SE tool to make sure that the service is always considering the correct topology of the grid. Beyond the grid data, which can be determined by the DSOs with a different degree of accuracy as the information of low voltage grids may be incomplete and inaccurate, the key point for enabling the SE service is the availability of measurement devices with real-time communication capabilities. Different from the transmission system, where a large coverage of devices is often available, the instrumentation penetration at the distribution level is usually poor with only few devices installed in specific points, like primary substations (high/medium voltage substations). As a matter of fact, the main power system requirement to enable the grid monitoring via SE is thus the deployment of devices providing the needed measurement data. Due to the large size of the distribution grids and obvious economic constraints, guaranteeing a full observability of the grid is mostly impractical and hardly achievable. The SE solution duly takes into account this aspect and aims at enabling the SE service using only few low-cost measurement devices deployed at strategic points of the grid (chosen by means of ad hoc meter placement strategies). Moreover, the conceived SE solutions are designed to maximize the accuracy performance even in presence of few measurement units in the field. However, it is worth noting that the accuracy of the estimation results strongly depends on the number of available measurements.

Needed components in the field: Information about the electrical grid: Type of measurements: Measurements number: Measurement accuracy: Measurement synchronization: Additional data needed from the field: Real-time communication capability: Bi-directional communication: Use of edge cloud:

The developed PC service is based on the operating conditions of the grid and processes this information to determine the optimal setting of active and reactive power generation for the distributed generation or, when available, of storage units. Different goals can be pursued to enhance the operation of the distribution grid, such as: the reduction of power losses during the operation with normal conditions; the minimization of voltage unbalance in case of high differences in the status of the three phases of the system; the minimization of possible active power generation curtailments during circumstances with over-voltage issues in the grid. The output of the PC service is a list of set points of active and reactive power (PQ set points) for the converter-based components connected to the grid. Consequently, the service needs bi-directional communication with the field to ensure proper delivery of the generated control commands. The design of the PC service is coupled with the State Estimation service. According to this idea, the PC service takes as input the results of the State Estimation service, namely the voltage profile at the different buses and the information about the branch power flows and the power consumption (or injection) at the nodes. Together with this information, the service needs as input also the model of the electric grid, expressed in terms of network topology and line characteristics. More specifically, the list of inputs needed to enable the PC service includes the following data. Static grid data:

• Electric grid topology (information about the nodes and the connection among the different nodes in the grid).
• Electric component parameters (e.g. impedances of the lines, impedances of transformers, etc.).

Real-time data:

• Estimation of the bus voltages, power flows in the branches, power consumption or injection at the nodes (as provided by the State Estimation service).
• Real-time notification of a change in a switch or breaker status.

The output of the PC service is the pair of active and reactive power set points for each converter-based component in the grid. The output of the power control service has to be sent to the converters in the field through communication technologies available in the field for control commands. Results can also be sent to the control room of the Distribution System Operator (DSO) for monitoring and can be stored in the database for possible a posteriori analysis. Since the PC service relies on the results of the State Estimation service, some of the power system requirements for this service are in common with the State Estimation service. First, measurement devices with real-time communication capabilities are needed to guarantee meaningful monitoring of the electric grid. The accuracy of the estimated results provided by the State Estimation service can also affect the performance of the PC service. Similar to the case of the State Estimation service, a critical challenge for the application of PC at distribution level is the large size of the distribution grids. This calls for the design of distributed approaches where PC services act on small areas, possibly sharing some data with an upper level controller to ensure the coordination of the power control strategy in the whole grid. Due to the active nature of this service, a bi-directional communication is needed with the field. Data are collected from the grid to enable the State Estimation service, while the output of the PC service is sent to the converter-based components for the control of their power generation (or consumption). This also implies the need to have converters able to communicate remotely, both for sending measurement data (if available) and for receiving the actuation commands. While converters available today do not always guarantee this behaviour, this requirement can be considered as realistic in future scenarios where the availability of communication capabilities is essential to enable the Smart Grid. The PC service runs continuously and synchronously with the State Estimation service. In particular, a new iteration of the service is triggered by the collection of a new set of estimation results provide by the State Estimation service. Similar to the case of State Estimation service, there are not strict requirements on the reporting rate for the PC service. However, due to the highly intermittent behaviour of renewable energy sources and the possibility of sudden changes in the operating conditions of the distribution grid, it is recommended to run the PC service with at intervals shorter than one minute and possibly close to a few seconds.

Needed components in the field: Information about the electrical grid: Type of measurements: Measurement number: Data volume: Measurement accuracy: Measurement synchronization: Additional data needed from the field: Real-time communication capability: Bi-directional communication: Communication reliability and security: