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Grid-connected ac microgrids (MG) are commonly exposed to voltage quality deterioration due to the presence of voltage imbalance. This article presents a control strategy that enables MG grid-feeding inverters (interfacing distributed generation units) to compensate for the voltage unbalance at a given remote node of the MG where for example a sensitive load is likely to be damaged. Each inverter is equipped with a new controller whose operation 1) allows to contribute in the control of the imbalance by only using a measure of the negative-sequence voltage at the remote node while 2) ensuring a fairly redistribution of the control effort among the participating inverters in terms of an inherent negative-sequence current sharing functionality. Since both control objectives are achieved without requiring the collaboration among the participating inverters, the presented solution offers an inherent robustness not found in previous state-of-the-art voltage unbalance control strategies. The new control strategy is accompanied by a controller parameter design receipt, and it is complemented by a formal analysis that permits evaluating how MG modeling errors and uncertainties affect stability and performance. Laboratory experimental results corroborate the properties of the presented control.

Unbalanced loads in islanded inverter-based microgrids induce voltage and current imbalances, posing significant challenges to the operation of critical equipment and sensitive loads. To address this issue, conventional circuit breakers, strategically placed between microgrids, play a key role in fault isolation during unbalanced conditions. However, they exhibit weaknesses in effectively addressing power quality issues, frequency variations, and power supply interruptions to specific loads. To solve these limitations, this article introduces the new concept of a negative-sequence virtual circuit breaker. Microgrid inverters are responsible for implementing this concept, which consists of eliminating negative-sequence voltages and currents at the point of-common-coupling between microgrids without altering positive-sequence voltages and currents. This last issue allows the entire electrical system to operate on a single frequency, guaranteeing the loads’ supply. The compensators responsible for implementing the proposed concept are unilateral bandpass filters with complex coefficients. The primary advantage of these compensators over conventional integral compensators is their ability to offer plug-and-play operation. The effectiveness of the proposed concept has been verified through experimental tests in a laboratory setup.

During voltage sags, three-phase three-wire power inverters can provide voltage support with several current injection strategies. In general, good results are obtained, except in overvoltage situations when one or more phase voltages exceed the allowed limit in grid codes. In three-wire inverters, this is a challenging problem because phase voltages are coupled. In this article, we present a strategy that performs independent reactive current injection for each phase, which solves the overvoltage problem. This approach also includes a current-limiting technique that guarantees the injection of the maximum active power under safe current conditions. A stability analysis is carried out based on the small-gain theorem. The properties of the proposed control are experimentally validated with selected tests in a laboratory setup. A performance comparison with state-of-the-art control strategies is also included in the experimental validation.

While most of the research work in the field of electrical engineering was aroused by the scientific challenges to be overcome, it is fair to recognize that the practical importance of engineering hinges on its economic impact on the market, the whole society and the environment. Thus, nowadays economic modeling, analysis and optimization of the electricity market is of the utmost significance. This work presents an aggregated economic analysis of the Brazilian electricity distribution companies using an economic model of a regulated market. The fundamental agents (consumer, power utility, government, society) are represented in the TAROT—Optimized Tariff Model, which is applied to the majority of the distribution companies in Brazil, based on public real data available from ANEEL—the Brazilian electrical energy regulatory agency. This reveals the economic flows in the regulated market of each company and also presents their financial status in terms of over-investments or under-investments compared to optimal investments and positive, negative or zero economic value added of each company. Moreover, the model analysis shows the socioeconomic welfare added to society in face of different optimization objectives.