Page 149 - Hybrid-Renewable Energy Systems in Microgrids

Study of control strategies of power electronics during faults in microgrids 133

Figure 7.7 (Continued)

inner current controllers to provide a voltage reference to the islanded microgrid.
Furthermore, the angle for Park Transformation is no longer provided by PLL in
islanded mode. To provide frequency regulation for an islanded microgrid, this
angle is typically generated through the voltage formation loop, which can be
designed in different ways.
Three typical control structures of the voltage formation loop are presented in
Fig. 7.9. In Fig. 7.9A, the voltage formation is directly decided by the desired voltage
amplitude and frequency references. The converter works like an ideal AC source
with a low-output impedance. If there is more than one converter being controlled