Page 60 - Hybrid-Renewable Energy Systems in Microgrids

44 Hybrid-Renewable Energy Systems in Microgrids

networks are generated. The decoupled AC network configuration is connected to
the AC-DC converter then it is connected to the DC-AC inverter operation, which is
directly linked to the power grid. On comparing these two network configurations,
coupled AC microgrid is less expensive [23].
A typical AC microgrid systems interconnected with medium voltage system at
the PCC is shown in Fig. 3.4. Solar panel, wind turbines, and ESS units are con-
nected to the AC bus through the DC–AC converter or AC–AC converter. Generally,
the RES units and load can form a small isolated AC electric power system called an
AC microgrid. Under normal operating mode, the AC coupled and decoupled net-
works are connected at the PCC, although the loads are supplied from the RES. If the
load demand power is smaller than the ability of power production of DG units, then
the large amount of power is often exported to the utility grid. Voltage and frequency
standards of the AC microgrid have been applied in conventional distributed power
systems.
In the distribution system, AC microgrids can be divided into single phase AC
and three phase AC - with and without neutral lines. The stability of the microgrid is
investigated under both the generation and load dynamics of the system. The stability
analysis of AC microgrid is generally damaged by the frequency droop coefficient
and it is developed by the dynamical manner of droop control. Small signal stability,

Figure 3.4 AC micro grid.