Ancillary Service in Active Distribution Systems from Renewable Energy Sources: Control Methodologies and Trends investigates suggested solutions for providing new ancillary services from distributed renewable energy sources in distribution grids. The book explores the control strategies of converter- interfaced renewable energy sources in the new electricity markets of active distribution networks. It describes how renewable energy resources can be utilized to provide primary control to the grid in reliable and secure ways. Useful for grid operators, regulators, and power system researchers, this book serves as a unique reference on auxiliary services for distribution networks. The stability and security of existing electricity power systems is largely based on the inherent characteristics of synchronous generators, such as grid-forming capability, inertia, damping of transients and large current contribution during grid faults. The increasing penetration of converter-interfaced renewable energy sources in the distribution grids is gradually replacing the dispatchable synchronous generators, increasing power volatility and causing large frequency deviations and voltage regulation problems. Therefore, new sophisticated control strategies for converter-interfaced sources combined with energy storage systems have emerged, enabling the operation similar to synchronous generators, which can be provided as ancillary services to active distribution systems.