Manuel Barragán-Villarejo

Distribution grids are facing a great transformation in recent years with the advent of smart grid technologies. Particularly, more and more controllable devices, based on power electronics, are being deployed in this part of the power system. These interfacing devices are in charge of the active power management of many resources ranging from renewable energy sources to energy storage systems. For this reason, it has to be considered that power electronics may provide valuable ancillary services for improving the operation of distribution networks. With this regard, it is important to stress that low-voltage distribution systems and microgrids are by nature unbalanced due to single-phase loads. Consequently, the flexibility requirements and control capacities of converters interfacing distributed resources have to be greater with respect to those of balanced systems. This work proposes independent power control for each phase of a three-phase, four-wire virtual synchronous generator specially suited for these unbalanced environments. The technical feasibility of the control approach has been successfully validated through several Control Hardware-in-the-Loop tests analyzing both steady-state and transient responses as well as the performance on a microgrid scenario. In this last scenario, the performance of the proposal has been also compared to a virtual synchronous generator based on symmetric components decomposition.

Real-time optimisation of microgrids is essential to unlock the flexibility provided by distributed energy resources while keeping operating costs low. This paper proposes a lightweight Artificial Neural Network (ANN) controller that emulates an Optimal Power Flow (OPF) solver and delivers set-points to controllable generators, according to real-time conditions. A systematic workflow for (i) synthetic data generation, (ii) ANN architecture design and training, and (iii) the integration of trained ANN within hardware-in-the-Ioop (HIL) simulation setup using the OP AL-RT real-time platform is presented. Experiments on the benchmark CIGRE medium-voltage network demonstrate that the ANN achieves a low mean-squared error, enabling true real-time deployment. Compared with conventional OPF execution, the proposed ANN approach reduces CPU utilisation by more than 99 %, while preserving optimality within 0.52 %.

Climate change has expedited the integration of converter-interfaced renewable energy sources (CIRESs) in distribution systems. Nevertheless, the active power volatility of CIRESs and the resulting high ramp rates are known to downgrade the voltage quality of distribution systems, causing rapid voltage changes (RVCs). In this context, the operation of CIRESs under ramp-rate limitation (RRL) schemes, employing an energy storage system, could serve as a preventive action against RVCs, thereby restoring voltage quality. To this end, this paper provides insights into the deployment of RRL control against RVCs in two stages. Firstly, the aptness of RRL as a preventive action is experimentally evaluated in a scaled-down laboratory testbed of the CIGRE European benchmark medium-voltage feeder, hosting CIRES prototypes. The RVCs are defined as per the IEEE 1547:2018 and IEC 61000-4-30:2015 Standards. The experimental results demonstrate that the operation of CIRESs under RRL control can enhance voltage quality by suppressing RVCs. Subsequently, a novel, system-level strategy for the coordinated mitigation of RVCs is developed. For a given distribution system, the proposed strategy allocates the RRL functionalities among CIRES units, to achieve the elimination of RVCs under minimal CIRES engagement and energy storage requirements. The effectiveness of the strategy is tested via dynamic rms simulations on the IEEE European Low Voltage test feeder.

The high penetration of renewable energy sources (RES) interfaced with power electronics together with new nonlinear loads pose new challenges in the grid operation. In fact, power systems with reduced inertia and high harmonic distortion will be common in a near future. Recently, the grid-forming operation of voltage source converters (VSCs) has emerged to address these challenges, mimicking the contribution of synchronous generators to the system inertia. In addition, these grid-connected VSCs can be used at the same time for reducing the harmonic distortion by applying active filtering techniques. However, these harmonic compensation algorithms can generate VSC overloading. This paper proposes a method for dynamically adjusting the individual virtual impedance of the filtered harmonics to prevent the power converter overcurrent. For this purpose, the value of each harmonic virtual impedance is modified according to a priority which can be set by the final user according to the established power quality standard. The paper includes a theoretical stability analysis of the controller and experimental results to validate the proposed algorithm.

The massive integration of distributed renewable energy resources is a reality in the current power system. In this new context with a greater volatility on the generation side it is required to incorporate new assets to provide additional flexibility to the system to accommodate as much renewable resources as possible. Among these new assets, DC or AC flexible links could play a key role in managing the power flows within radial distribution systems. These connected between distribution feeders may regulate the active power flow in a controlled manner and contribute to the network voltage support. However, the power losses of these devices can be a limiting factor of some functionalities. This paper integrates a detailed power loss model of several flexible link topologies for Optimal Power Flow algorithms with the aim of evaluating its impact on the functionalities of these devices. In this way, it is possible to benchmark the performance of different DC and AC flexible links in a quantitative manner by means of some key performance indexes. The paper proposes a case study based on the European MV benchmark with a high penetration of renewable energy sources to evidence the benefits and limitations that flexible links may provide.