Abstract
In this paper a real-time laboratorial experiment is presented, intended to validate a 'grey-box' equivalent model for medium voltage active distribution networks with high presence of converter-connected generation, considering the latest European grid codes requirements, in response to severe faults at the transmission network side. A hybrid setup was implemented at INESC TEC's laboratory (Porto, Portugal), relying on a real-time digital simulator to provide the interface between simulation and physical assets available at the laboratory, in a power-hardware-in-the-loop configuration. The study considered the laboratory's internal network to be operating (virtually) as a medium voltage distribution network with converter-connected generation (fault ride through compliant), connected to a fully-detailed transmission network model. The aggregated reactive power response of the laboratory's network was fitted by the dynamic equivalent model, recurring to an evolutionary particle swarm optimization algorithm. The methodology adopted, testing conditions and respective results are presented. © 2019 IEEE.

Abstract
Smart Transformers (STs) are being envisioned as a key element for the controllability of distribution networks in a future context of Renewable Energy Source (RES), Energy Storage System (ESS) and Electric Vehicle (EV) massification. Additionally, STs enable the deployment of hybrid AC/DC networks, which offer important advantages in this context. In addition to offering further degrees of controllability, hybrid AC/DC networks are more suited to integrate DC resources such as DC loads, PV generation, ESS and EV chargers. The purpose of the work developed in this paper is to address the feasibility of exploiting STs to actively coordinate a fleet of resources existing in a hybrid AC/DC network supplied by the ST aiming to provide active power-frequency regulation services to the upstream AC grid. The feasibility of the ST to coordinate the resources available in the hybrid distribution AC/DC network in order to provide active power-frequency regulation services is demonstrated in this paper through computational simulation. It is demonstrated that the aforementioned goal can be achieved using droop-based controllers that can modulate controlled variables in the ST.

Abstract
Large horsepower induction motors play a critical role as industrial drives in production facilities. The operational safety of distribution networks during the starting transients of these motor loads is a critical concern for the operators. In this paper, an analytical and convex optimization model is derived representing the starting transients of the induction motor in a semi-static fashion. This model is used to find the optimal energization sequence of different loads (static and motor loads) following an outage in a distribution network. The optimization problem includes the optimal control of the converter-based DGs and autotransformers that are used for the induction motor starting. These models together with the semi-static model of the induction motor are integrated into a relaxed power flow formulation resulting in a Mixed-Integer Second Order Cone Programming (SOCP) problem. This formulation represents the transient operational limits that are imposed by different protection devices both in the motor side and network side. The functionality of the proposed optimization problem is evaluated in the case of a large-scale test study and under different simulation scenarios. The feasibility and accuracy of the optimization results are validated using I) off-line time-domain simulations, and II) a Power Hardware-In-the-Loop experiment.

Abstract
The development of future HVDC grids for transnational interconnections and offshore wind farms development should be compliant with specific requirements regarding frequency support and inertia emulation. Therefore, this paper presents the development of communication-free control solutions capable of dealing with these control requirements. The proposed solution exploit a coordinated control approach between offshore wind turbines and VSC-HVDC converter stations based on the DC grid voltage modulation. The effectiveness of the proposed control solutions are demonstrated to be of utmost importance for improving future grids frequency regulation capabilities. Recognizing that numerical simulations provide valuable knowledge regarding HVDC grids operation and control, this paper introduces a further step encompassing the development of a reduced scale laboratorial prototype of a DC grid making possible the demonstration of key frequency control functionalities. Following the theoretical/conceptual background that is demonstrated through numerical simulation, laboratorial tests were then performed in order to test and demonstrate the performance and effectiveness of the proposed control mechanisms that future HVDC grids will provide to frequency control in mainland AC grids.

Abstract
The integration of distributed Battery Energy Storage Systems (BESS) at the Medium Voltage (MV) and Low Voltage (LV) networks increases the distribution grid flexibility to deal with high penetration of Renewable Energy Sources (RES). In addition, it also enables the deployment of key self-healing functionalities, which allow the islanded operation of small sections of the distribution network. However, new planning and real-time operation strategies are required to allow the BESS coordinated control, as well as a cost-effective and stable operation. This paper presents new tools developed for the planning and real-time operation of distribution networks integrating BESS, particularly when operating islanding. For real-time operation, a short-term emergency operation-planning tool assesses the feasibility of islanded operation of a small section of the distribution network. The long-term impact of a BESS control strategy for islanded operation is assessed through a Life Cycle Analysis (LCA) tool. The results and implementation experience in real distribution network are also discussed.

Abstract
Large horsepower induction motors play a critical role in the operation of industrial facilities. In this respect, the distribution network operators dedicate a high priority to the operational safety of these motor loads. In this paper, the induction motor starting is modeled analytically and in a semi-static fashion. This model is imbedded in a convex distribution system restoration problem. In this optimization problem, it is aimed to determine the optimal status of static loads and the optimal dispatch of distributed generators such that: a) the induction motors can be reaccelerated in a safe way and, b) the total power of static loads that cannot be supplied before the motor energization, is minimized. The proposed optimization problem is applied in the case of a distribution network under different simulation scenarios. The feasibility and accuracy of the obtained results are validated using a) off-line time-domain simulations, and b) Power Hardware-In-the-Loop experiments.