Advanced Control and Coordination Methods for Power Electronic Converters in Microgrids

Environmental considerations are driving the development of modern power systems, leading to an increasing presence of renewable energy sources and power electronics converters that interface them with the electrical grid. The inherent variability and unpredictability of renewables motivates their clustering into microgrids, which can provide local energy storage and smart load management. In this scenario, proper control of power converters is crucial to enable the required orchestration of the distributed energy resources. This dissertation addresses critical challenges in terms of functionalities and power control capabilities of distributed power converters, which form the basis of the effective integration of distributed energy resources. Its contributions can be conceptually divided into two parts: the first one tackles classic limitations of grid-forming converters in terms of control flexibility compared to their grid-following counterparts; the second one studies the coordination of multiple converters in a microgrid, leveraging the newly unlocked degrees of freedom to improve its operation and to provide ancillary services to the upstream grid. More specifically, in the first part two novel control approaches based on droop-control are proposed to provide grid-forming converters with unbalanced operation capabilities, allowing the compensation of non-balanced load conditions or the tracking of unbalanced references. A low-voltage ride through technique is then proposed for flexible grid-forming converters that enables them to withstand balanced and unbalanced faults, still retaining the introduced enhanced control capabilities. In the second part a coordination algorithm is proposed for converters to optimize their operation in microgrid scenarios. This method minimizes the power losses due to reactive and unbalanced currents, optionally offering their total compensation at the point of common coupling with the upstream grid. The method perfectly integrates with energy managing techniques, as it does not modify the active power exchange. Finally, an experimental setup is developed for the validation of microgrid control methods. The setup employs 10 power electronic devices and a communication network to offer a holistic validation approach, encompassing hardware aspects and all the control layers. It is used to experimentally validate the microgrid coordination approach while integrating the developed local control techniques for the converters. As power systems undergo fundamental transformation toward power-electronics-dominated, highly distributed architectures, the conducted studies aim to provide critical building blocks for more resilient, efficient, and economically viable distributed energy systems that will help achieve the electrification and environmental goals driving modern power grid development.