Flexibility and reliability of ac microgrids are enhanced by reducing the dependence on communications in multilayer hierarchical control. In this sense, this paper presents a secondary control with no communications for islanded microgrids. It is based on a control scheme that switches between two configurations according to a time-dependent protocol. With this proposal, an excellent performance in terms of transient response and frequency restoration in steady state is achieved. This paper also presents design considerations for the control parameters. In addition, the theoretical predictions are validated by experimental results from a laboratory microgrid.

This paper presents a distributed strategy for the optimal dispatch of islanded microgrids, modeled as unbalanced three-phase electrical distribution systems (EDS). To set the dispatch of the distributed generation (DG) units, an optimal generation problem is stated and solved distributively based on primal-dual constrained decomposition and a first-order consensus protocol, where units can communicate only with their neighbors. Thus, convergence is guaranteed under the common convexity assumptions. The islanded microgrid operates with the standard hierarchical control scheme, where two control modes are considered for the DG units: a voltage control mode (VCM), with an active droop control loop, and a power control mode (PCM), which allows setting the output power in advance. To assess the effectiveness and flexibility of the proposed approach, simulations were performed in a 25-bus unbalanced three-phase microgrid. According to the obtained results, the proposed strategy achieves a lower cost solution when compared with a centralized approach based on a static droop framework, with a considerable reduction on the communication system complexity. Additionally, it corrects the mismatch between generation and consumption even during the execution of the optimization process, responding to changes in the load consumption, renewable generation and unexpected faults in units.

In this paper, a new and generalized model for the optimal operation of microgrids is presented. The proposed mathematical model considers both operational modes, either grid-connected (GC) and islanded (IS) modes. First, a mixed integer non-linear programming (MINLP) formulation is introduced, modeling the microgrid as an unbalanced ac three-phase electrical distribution system (EDS), comprising distributed generator (DG) units, battery systems (BSs) and wind turbines (WTs). In GC mode, the frequency and the voltage magnitude references are imposed by the main grid at the point of common couple (PCC), while in IS mode, it is assumed that the DG units operate with droop control. Additionally, a set of convexification procedures are introduced in order to approximate the original MINLP model into a new convex formulation that can be solved using commercial solvers. The proposed model has been tested in a 25-bus microgrid for different scenarios, including one where a degradation of the voltage magnitude reference is observed. Results shows that the proposed model is able to properly define the operational mode of the microgrid, based on the technical constraints of the system.

In recent years, microgrids have gained attention as a technological alternative to face the energy transition and universal sustainable electrification challenges. Its versatility to operate in grid-connected or isolated mode allows adapting the microgrid concept to several urban and rural applications. This has motivated industry and academia to develop experimental projects, prototypes, and application pilots worldwide. This paper presents a review of some laboratories and test systems of microgrids in Latin America. A brief description of the general information of each microgrid and its main characteristics and components are presented. Also, a discussion of the main advances in distributed generation in Latin America is included