Microgrids should satisfy a number of demands and expectations of various stakeholders and customers in the electrical energy chain. Their heterogeneity demands the identification of a microgrid’s operation policy in a bid to address a number of targets related to efficiency, resiliency, power quality, and affordability. The operation policy should consider the presence of distributed energy sources including generating units, storage systems and responsive loads, which can pose positive effects in view of efficiency as well as sustainability of the system, but also pose negative effects to be carefully taken into consideration in view of power quality and reliability.
The uncertainties of some generating units and of loads are focal for line overloading as well as critical voltage profiles. In addition, unexpected peak power in demand or in generation can result in problems of matching loads and generations. The problems of power quality are even more pronounced for low voltage microgrids characterized by unbalanced lines as well as uneven distribution of single phase loads and generators. .
Unbalance in phase voltages along with the consequent flow of large unbalanced currents may increase losses as well as heating effects, therefore, compromising power electronic converters and motors. For the case of low voltage microgrids, the presence of characteristic and non-characteristic harmonics and zero-sequence components in the currents flowing through the neutral conductors lead to overloading of transformers and distribution feeders.
Guido Carpinelli and colleagues at the University of Naples Federico II and University of Cassino and Southern Lazio in Italy proposed a detailed strategy for the scheduling of unbalanced microgrids. They characterized the microgrids by the presence of a number of distributed resources such as plug-in electric vehicles, distributed generation systems, and data centers. Their research work is published in Applied Energy.
The operation of the proposed approach was founded on the solution of a multiobjective optimization problem, whose primary objective functions were related to particular services and needs of the microgrid, which included power quality improvements, energy savings, and cost optimization. The authors paid particular attention to the unbalance presence in the microgrid aiming at outlining how the proposed optimization method would be able to considerably reduce them and to satisfy other economic and technical aspects.
The authors, therefore, proposed an analysis of possible objectives related to various operational perspectives. This allowed for the exploitation of the effectiveness of the multi-objective approach.
The multiobjective approach for the scheduling of unbalanced microgrid was developed taking into account a number of distributed resources. The aim of the proposed strategy was to reduce unbalances effects, unavoidably present in low voltage microgrids and to consider other critical technical and economic objectives. An evaluation of the outcomes of the numerical applications indicated the effects of the considered strategy in view of achievable technical and economic benefits.
The research team observed that a considerable contribution to the unbalances also could be given by the microgrid’s resources such as data centers and plug-in electric vehicles. This displayed the importance of a coordinated control in a bid to exploit the potential of the resources while maintaining the satisfaction of power quality and of other microgrid’s operation necessities. The proposed scheduling provided advantages in terms of efficiency and savings even when focused on power quality issues including voltage deviation and unbalances.
Carpinelli, F. Mottola, D. Proto, and P. Varilone. Minimizing unbalances in low-voltage microgrids: Optimal scheduling of distributed resources. Applied Energy, volume 191 (2017), pages 170–182.Go To Applied Energy