As the penetration of Converter-Interfaced Dis-tributed Renewable Energy Sources (CI-DRES) increases, several problems are revealed in electric power systems, e.g., power quality issues, reverse power flows and frequency instability. A solution to tackle these issues is the mitigation of high CI-DRES active power ramp-rates (RRs) by utilizing energy storage systems (ESS). In many grid-codes at transmission system (TS) level, it is specified that the CI-DRES limit their RRs, while also the utilization of a central ESS has been proposed to limit the RRs. Nevertheless, this approach involves only large energy market players. Although various RRL methods have been proposed for CI-DRES, a remaining gap is the evaluation of the RR of a Distribution Network (DN) containing CI-DRES and loads together with the influence of distributed ESS in the DN. Towards this direction, in this paper, this evaluation is performed in order to study the RRL capability of a low-voltage (LV) DN considering both central and distributed ESS. The analysis is conducted in the LV CIGRE DN via quasi-steady-state and RMS simulations in PowerFactory considering several techno-economic parameters, e.g., ESS size, type, per unit cost. This evaluation will help towards the integration of the RRL control in the grid codes in DNs so that it can be considered as a new ancillary service to be remunerated in respective markets where also small CI-DRES owners will be able to participate.@en

This paper deals with a systematic assessment of the power system frequency dynamics under high penetration of converter-interfaced renewable energy sources (CI-RESs). Specifically, the concept of the virtual synchronous generator (VSG) is implemented in the CI-RESs located at the transmission system (TS) side and/or the distribution network (DN) side. Dynamic RMS simulations are performed on a testbed consisting of the IEEE 9-bus TS grid and the CIGRE medium-voltage DN grid under different CI-RES penetration levels and VSG control parameters to assess the VSG impact on the power system frequency dynamics. It is shown that the decommissioning of conventional power plants coupled via synchronous generators can be safely performed in case the VSG concept is adopted correctly.@en

The increasing penetration of renewable energy sources is strongly linked to the development of voltage source converters used in their connection to the grid. As a result, in the near future of an inverter-dominated power system it will be a requirement for renewable generation to provide ancillary services in order to compensate for the absence of synchronous generation. In this scenario, the use of energy storage systems along with advanced control algorithms mimicking the dynamic behaviour of the traditional generators will be of utmost importance. This paper deals with a renewable energy source interfaced with a voltage source converter and comprising an energy storage system in the DC bus. Particularly, a new energy management algorithm for the DC-bus based on a three levels hierarchical control is proposed, which is able to simultaneously provide ancillary services, maintain the state of charge of the storage system within the permissible limits and use it to control the DC bus voltage. The control strategy is validated experimentally using a prototype with results evidencing a reliable and stable operation.@en