Abstract
The content of this paper aims to assist in the development and implementation of microgrids by addressing the challenges and possible solutions for their protection systems. Therefore, an overview of some protection methods available in the literature that can be implemented to ensure a safe and reliable microgrid operation is presented, including the most common protection devices and earthing schemes that can be adopted in low voltage distribution systems. In addition, this paper also presents a brief fault analysis of internal faults at three different locations in an industrial microgrid with centralized and decentralized deployment of energy sources, as well as a short-circuit analysis of symmetric and asymmetric faults at these faulty locations. An approximate method based on the calculation of the equivalent impedance seen from the fault location is used to determine the fault currents. This study is made to observe how microgrids with different configurations perform in the event of internal faults. It is demonstrated in this work that setting a specific protection strategy to allow the microgrid to operate effectively during both operation modes can be problematic and expensive in most situations. With this in mind, additional effort is necessary to engineer and implement new protection approaches that can overcome the limitations of protection systems in future microgrids.

Abstract

Abstract
European governments' targets for renewable energy by 2020 will lead to large offshore wind power integration in the existing Power System. High-Voltage Direct Current (HVDC) provides the most suitable technology to enable massive integration of offshore wind farms into AC onshore grids over long distances, with great control on transmitted power. More specifically, DC Grids (DCG) based on Voltage Source Converters (VSC) are being widely investigated to integrate multiple offshore wind farms dispersed over wide areas into AC onshore networks. For three and a half years, the « DC GRID » demo within the TWENTIES European project was focussed on a wide range of challenging issues related to the DC grid benefits for connecting offshore intermittent power: offshore DCGs economic assessment and likely layouts; DCG control and protection; ancillary services provided by such grids to the mainland AC network. This paper presents major achievements of the TWENTIES project in these domains. In addition, two major outcomes of the « DC GRID » demo are physical demonstrators. One of them is a low scale DCG mock-up, on which some of the above controls, as well as DC grid protection algorithms were successfully tested. Last, a highly innovative DC Circuit Breaker (DCCB) prototype was developed to overcome a strong technological barrier: this new equipment was successfully tested in presence of an independent expert to establish the qualification of this technology in the HV domain.

Abstract
In the decades to come spatial limitation poses a major challenge for islands, especially where tourism dominates and many heritage and natural conservation sites exist. Simultaneously, alternatives to lower energy import dependency are sought. Since onshore technologies are confronted by spatial limitation, the focus might shift towards integrating offshore technologies. Although most of those technologies lack market maturity, the benefit to be installed (far) off the coast is immense. Yet, it is a challenge to select the most appropriate technology for any given site location. Thereby, it is not pre-dominantly a matter of economic and environmental concerns, rather than an assessment of site conditions and resource characteristics. A set of indicators for, both, conditions and characteristics has been established that allows pre-selecting and comparing the suitability of various offshore technologies. Hence, energy planners will be able to select from the most appropriate technologies when planning for a sustainable future. © 2015 Taylor & Francis Group, London.

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 micro-generation (µG) in distribution networks faces new challenges concerning the technical as well as commercial management. The µG integration in the Low and medium voltage distribution networks has many advantages for the grid operation, such as voltage profiles improvement, power losses reduction, and branches congestion levels reduction. This paper presents a method for guiding continuation power flow simulation of integrating µG on distribution feeders. A base model is designed with variable capacitor bank, µG unit such as PV and Wind generation are integrated. A control method is used to improve the voltage level of each node as well as improving power factor of the systems. The electricity consumption of a university's substation area where commercial, residential and municipal load are presented are modeled using actual data collected from each single residential hall and commercial buildings. This model allows analyzing the power flow and voltage profile along each distribution feeders on continuing fashion for a 24- hour period at hour-by-hour formulation. By dividing the feeder into load zones based on distance from each load node to distribution feeder head, the impact of integration of different µG operation in different condition has been discussed. © 2019 IEEE.