Resumen de Control of distributed renewable energy generation systems in converter-dominated microgrid applications
There is a growing interest in the use of renewable Distributed Energy Resources (DERs) that increase the efficiency of the transmission system and reduce the ecological impact of Renewable Energy infrastructures. At the same time, they reduce the associated capital requirements, thus increasing the potential installation of renewable energy.
Microgrids have been proposed as a solution to improve the integration of DERs. By the use of advanced control techniques, they provide a reliable frame for DERs to support the power system operation. As such, Microgrids can be a promising solution to increase renewable energy penetration. However, since renewable DERs are usually interfaced by Power Electronic Converters (PECs), they do not provide the common stabilization characteristics of traditional generation interfaced by Synchronous Generators (SGs). Therefore, there are concerns about the stability of converter-dominated Microgrids.
This Thesis focus on the specific requirements of PEC-interfaced renewable DERs operating in Microgrids. A general overview of current the control systems show that for PECs to support the Microgrid operation in both grid-connected and islanded modes, they require a synchronization system that does not rely on the measurement of an external frequency. A promising alternative is to replicate the behavior of traditional SGs in the PEC control system with the so-call Virtual Synchronous Machine (VSM) solutions. The synchronization system underlying to these proposals is analyzed. A comparison with the use of traditional frequency measurement systems, namely Phase-Locked Loops (PLLs), in the support of the Microgrid power balance is addressed, showing that the PEC synchronization system has a direct effect on the Microgrid stability.
The Thesis includes a new proposal for synchronization based on the use reactive power, instead of active power as in VSMs, that does not require frequency measurements. By the use of reactive power, the PEC active power can be controlled independently of the synchronization system. This Reactive Power Synchronization system is used to propose a solution for the black-start of Wind Energy Conversion Systems (WECSs), so that they can contribute to the restoration of the power system following a blackout.
