Page 134 - Hybrid-Renewable Energy Systems in Microgrids

118 Hybrid-Renewable Energy Systems in Microgrids

be nullified with two extreme cases k = − 1 and k = 1. When k = 0, the output current
from VSI is completely balanced under unbalanced faults. It is worth mentioning
here that the flexible scalars k and k can also have other values or relationships. In
q
p
Fig. 7.4, the short-circuit response of the VSI subject to a phase A-B fault with 0.1 Ω
is given and only three most representative scenarios are illustrated for brevity.

3.2 Flexible positive- and negative-sequence power control
According to Eqs. (7.22) and (7.23), the constant power components consist of pos-
itive-sequence and negative-sequence power terms. With the objective to flexibly

Figure 7.4 Short-circuit response of VSI with flexible oscillating power control. (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).