## 3 Energy Management System in Islanded Microgrids under Communication Constraints  
Real-time communication supports grid smartness, but with high energy consumption. In islanded conditions, this situation may be trouble since the energy availability is time limited. To ensure the maximum supply time, the hybrid energy management system defines a rank of priority loads connected to the system. The loads are classified according to the supply voltage, and also according to economic and social criteria. The rank is composed by residential, rural, commercial and essential loads.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Communications Requirements** & **Latency (time)** \\ \hline Distribution Management & 100 ms–2 s \\ Demand Response & 500 ms–several minutes \\ Advanced metering infrastructure (AMI) & 2 s \\ Transmission Line Monitoring & 15 ms–200 ms \\ Wide-Area Situational Awareness & 15 ms–200 ms \\ Substation Automation & 2 s–4 s \\ In-Home Communications & 2 s–15 s \\ Meter Reads & 2 s–15 s \\ Fault Location, Isolation, & 1 ms–10 ms \\ and Restoration for Distribution & 1 ms–10 ms \\ Outage Management & 1 ms–10 ms \\ Synchrophasor & 20 ms–200 ms \\ Site Surveillance & few seconds \\ \hline \hline \end{tabular}
\end{table}
Table 1: Communication requirements for a microgrid scenario.  
The highest grade load is the essential one, which includes survival services. When absent, it may bring danger to the health and safety of people. However, different from the previous approach [24; 25], the telecommunications loads are no longer considered a priority rank load, as the EMS adjust the need of communications load according to the grid operation status. The load classification is determined according to the Brazilian Electrical Energy Regulatory Agency and Table 2 illustrates each operating mode.  
The work conducted here deals with the adjust of communication network load according to different microgrid operation modes, determined by the current load, energy stored, and environmental conditions. Three different operation modes are proposed: normal, emergency and critical. Each of these operating modes has a list of predefined actions.  
In normal conditions, the microgrid is supplied by the main grid and the distributed energy resources. The MGCC receives and gathers all necessary information to evaluate the system's balance. During any fault or an outage, the microgrid is disconnected and supply loads using its distributed resources.  
Operating in islanded manner requires strict needs to ensure power availability for a longer time. The grid's primary goal is to supply the essential services for as long as possible. Thus, the EMS must consider maximizing the amount of provided customers during a minimum period, considering mainly the highest priority loads to ensure safer balancing conditions and lower frequency variations.  
Since it is not possible to determine the duration of the grid unavailability in the islanded operation, it is of paramount importance to supply the high-rank loads for the longest available time. This goal may be accomplished applying the energy management approach to maximize the time of power supply with the least possible cost while meeting the priority classes. The EMS determines the best grid operation mode according to the information gathered from the system and organized into different control variables used for decision-making. These operation modes have predefined schedule actions including load shedding of lower and medium priority customers and demand response steps to assure the best timing operation. The proposed hybrid method approach for application in microgrid's islanded operation is described in the next sections.