Maza Ortega, José MaríaBarragán-Villarejo, ManuelMatas Díaz, Francisco Jesús2025-03-312025-03-312024-12-17Matas Díaz, F.J. (2024). Control of Voltage Source Converters for Enabling Grid-forming Capability and Ancillary Services in Power Systems. (Tesis Doctoral Inédita). Universidad de Sevilla, Sevilla.https://hdl.handle.net/11441/171181Political and industrial efforts are focused on the decarbonization of the electrical system. To do this, conventional synchronous generators are being replaced by new renewable energy sources connected through converter-interfaced generators. Consequently, the new power system is mainly characterized by a reduced inertia, among other issues. The massive penetration of renewable energy sources at all levels of the distribution system is causing new challenges such as bidirectional power flows, voltage issues and unexpected overloads. Moreover, the exponential increase of power electronics is also occurring on the demand side, along with other types of non-linear loads. The proliferation of this type of devices in a progressively weaker grid has caused a generalized empourishment of the waveform quality in the power system, leading to more distorted nodal voltages, harmonic pollution, increased imbalance, neutral wire saturations and a general augment of power losses at transmission lines and electrical machines. In this scenario, the converter-interfaced generators, characterized for their fast response and control versatility, will have the titanic endeavour of providing a set of new functionalities, the so-called ancillary services, as solutions to these newcoming challenges. Virtual inertia must be provided to reinforce the frequency stability, the volatility of the renewable primary resources need to be smoothed, and the voltage levels and harmonic generation must be kept under control. Futhermore, the reduction of inertia in the power system and the proliferation of islanded systems have inevitably led to a new paradigm in voltage source converter control, where new advanced grid-forming control strategies are being deployed along with the traditional grid-following converters. This thesis provides contributions to address all the exposed issues. First, for the islanded mode of operation, an alternative methodology based on a virtual conductance is proposed for designing the classical free-running cascade voltage controller. As a continuation of this work, the outer control loops based on a virtual synchronous generator are implemented. The final solution is also extended from three-phase to single-phase systems. Second, for the grid-connected mode of operation, a full state-space model of a total of six combinations of the most extended outer and inner control loops for grid-forming converters has been developed. An analysis of the synchronization stability and dynamic performance of these schemes, as well as their suitability for different ranges of grid impedance is provided. Additionally, following this methodology, the critical control parameters are identified and re-tuned to extend its stability range. Furthermore, a complete sensitivity analysis of the control parameters for one of the combinations is provided. Finally, this thesis contributes to the research on ancillary services concerning power quality. An active harmonic filtering functionality, which incorporates a selective overcurrent limitation, is proposed for the grid-forming converter in both islanded and grid-connected modes. The state space model has been extended to include this ancillary service and its interaction with the virtual synchronous generator has been deeply studied. As an additional contribution, this thesis provide some insights into the interaction between the provision of ancillary services which require of a fast response of the active power as virtual inertia and the management of a low-capacity energy storage system.application/pdf205 p.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/info:eu-repo/semantics/doctoralThesisinfo:eu-repo/semantics/openAccess