Page 148 - Hybrid-Renewable Energy Systems in Microgrids

132 Hybrid-Renewable Energy Systems in Microgrids

Figure 7.7 Short-circuit response of VSI with flexible oscillating power control (current
limited). (A) Constant active power control (k p = − k q = − 1). (B) Balanced current control
(k p = − k q = 0). (C) Constant reactive power control (k p = − k q = 1). (Voltage: V; Current: A;
Power: kW/kvar).
4.1 Basic control structure

Fig. 7.8 gives the basic control structure of a VSI that provides voltage and fre-
quency regulation in islanded mode. In contrast with Fig. 7.1, a voltage control
loop is added before the inner current control loop and the references of the
voltage control loop are generated by a voltage formation loop. The responsi-
bility of the voltage control loop is to regulate the voltage at the PCC through