Page 120 - Hybrid-Renewable Energy Systems in Microgrids

104 Hybrid-Renewable Energy Systems in Microgrids

and frequency, plug and play capability in DERs, avoiding the flow of circulating cur-
rent and islanding detection with the ability to work both connected to the network and
disconnected from the network [40,41].

4 Dynamic security of microgrids

The first step for saving the dynamic security of the microgrids is deciding the effec-
tive components, which steer microgrids toward the instability. These elements incor-
porate a low inertia constant, frequency fault occurrence, and deficiency of existing
protection plans [42]. With respect to the issue of frequent fault occurrences, there
exist two reasons that strengthen the probability of phase-to-phase and three-phase
fault occurrence in microgrids [43]:
• Low clearance between conductors of the overhead lines;
• High probability of inter-circuit and developing deficiency event because of the ionization of
the air resulting to the phase to ground faults.
• Attendance of uncontrolled outside reasons, for example, the human activities
The execution of the protection system is one the most significant factors, which
risk the dynamic security of the microgrids. Participation of a reliable protection sys-
tem is of essential significance to keep away from dynamic instability [44]. For con-
ventional distributed systems, current-based protection relays were sufficient, because
of the radial structure of the system. In the microgrids, current-based relays might be
wrong for a few reasons [45]:
• Bidirectional power flows forced by DERs;
• Continual fault level variety caused by different working modes, that is, grid associated or
• islanded;
• Low fault currents forced by the establishing systems of DERs; and
• Constrained blame ride-through capacity of the inverter based distributed energy sources
The protection challenges of the microgrid were classified into the sensitivity mat-
ter, sympathetic tripping issue, and reclosing difficulties. Among these challenges, the
sensitivity matter and reclosing issue have direct bearing on the dynamic security of
microgrids.

4.1 Challenges in microgrid
Notwithstanding the various examinations done in this field, none of the proposed
control strategies can be favored as an ideal solution for remunerating all the power
quality prerequisites in the meantime. Future research ought to in this manner focus
on the novel power electronic control technique to fulfill all the said necessities in
the meantime. Also, the proper investigation is needed in the energy services such as
demand response, optimal power flow, market participation, and storage management.
The future patterns in control strategies for islanded microgrid are basically identified
with the following points such as cyber security improvement, Droop schemes based