One of the challenges faced by Brazilian distribution utilities to enable the connection and operation of microgrids (MGs) is the absence of a solid set of technical standards in the country. An alternative has been to use and adapt existing standards applied to micro- and mini-distributed generation. In this context, this paper presents an analysis of the development status of norms, standards, and general requirements for the connection and operation of microgrids, as well as a proposal for the regulation and structuring of technical and operational requirements related to the implementation of microgrid projects. Some critical points highlighted in the paper include: the modes of operation, the minimum requirements for the different modes of operation, interoperability of systems, a conceptual model with attribution of responsible actors for the decentralized management of microgrids adapted to the institutional standards of the Brazilian sectorial model, a proposal for a standard connection structure considering the point of connection (PoC) implanted using multifunctional relay and recloser, procedures for technical feasibility assessment (operational studies) of MGs connection, and, finally, a discussion of operational issues of storage systems in a microgrid environment.

This article reports the conception and design of a mission critical microgrid to serve a critical infrastructure application, namely, the Alcântara Space Launch Center, a government military facility in Brazil. The assumptions, general characteristics, requirements and particularities arising from the application are established and discussed in detail. High resilience and energy security are required in critical periods of operation, demanding a power supply infrastructure composed of redundant and dispachable sources capable of supporting $n-1$ generation contingencies. Whereas, in the remaining time, economic and environmental aspects take place as main requests. Operation scenarios, on both grid-connected (on-grid) and isolated (off-grid) modes, are formulated as optimization problems and simulations have been performed to analyze these scenarios, which are reported and analyzed here. The off-grid operation, which is clearly more complex, is preferentially addressed, especially in scenarios with contingencies. In this context, the proposed microgrid is conceived to satisfactorily balance requirements such as the economy, pollutant emission reduction, high reliability, resilience and operational security, which are requested by this critical infrastructure application.

Blade Element Momentum Theory (BEMT) is the most used method to design horizontal-axis wind turbines worldwide. This is because BEMT has a low computational cost and easy numerical implementation. Additionally, it is demonstrated in the literature that the prediction of output power using BEMT agrees well with experimental data. Another important feature of the BEMT is its applicability to small, medium, and large-sized turbines. However, BEMT models are usually implemented and adjusted for a specific power range turbine, and they are not applied in a more general form. Thus, this article presents an analysis of additional correction methods for tip and root losses, high values of the axial induction factor, and high angle of attack to better represent horizontal-axis turbines in terms of numerical stability. The approach has the intention of combining several complementary correction methods strategically inserted in the BEMT in order to compile an algorithm that is more general, stable, and workable for any turbine size. The main contribution of this work is to propose a stable BEMT numerical algorithm through the assessment of the combination of the correction methods available in the literature, i.e., classical and modern ones. The algorithm ensures applicability for small, medium, and large-sized wind turbines, as well as being fast and easy to implement in any computer and extendable even to turbines with a diffuser. This approach is validated by comparing the results with experimental data from four turbines of different power ranges (1.9 kW to 7.3 MW). The results show the best approximations for performance power curves against the measured values of all turbines. Moreover, it is effective, less complex, and quick in analyzing the performance of those turbines. Furthermore, the need for high-performance computers to analyze the performance of horizontal-axis turbines is avoided.

Isolated microgrids need dispatchable energy sources to ensure continuity of service during lack of the renewable energy sources. One common source is the diesel generator which is used as a backup and for battery charges. Practical experiences have shown that microgrids have operation problems when diesel generators and rectifiers work together to charge battery banks. This is because of resulting diesel generator voltage distortions caused by the interaction of line currents harmonics with equivalent series reactance of the AC source and the notches introduced during the current commutation between 2 SCRs of the bridge rectifier. These distortions eventually inhibit the rectifier operation, causing malfunctioning of the system. One solution is to use generators with rated power greater than the rectifiers, which results in oversized installation and high operating costs. This work proposes a solution to avoid generator oversizing by using resonant filters, notch filter and a capacitive reactive compensation circuit to avoid self-excitation of the generator. Soft-start operation of the rectifier, and disturbance decoupling in the generator are also proposed. The design allows the use of generators and rectifiers of similar power, reducing the installation and operation costs of microgrids. It has been used successfully in two real-life microgrids.

Around the word a significant number of villages may never have access to electricity due to their remoteness. For the people living in these isolated communities, access to renewable energy sources is the only solution to meet their energy needs. In these communes the electricity is mainly used for household purposes such as lighting. One of the main problems of such systems, located in isolated areas of difficult access, is the reliability. The coordination protection and operation, distribution network, inverters, control strategies, and maintenance are aspects that must be well designed to get a reliable system. Furthermore, in these applications the system should have the following features: expansion flexibility and robustness, high efficiency, and adequacy to operate in adverse environmental conditions. The results presented in this paper will address these problems with special attention to the control strategies, and system operation. The paper will present experimental results showing the robustness and viability of a pilot renewable hybrid electrical generation system in the Lençóis´s Island, northeast of Brazil.