Control and Design of Microgrid Components - Power Systems ...

Figure 5.6 Unit 2- Two Units in Parallel. [50ms/div]
Figure 5.7 shows the 120Hz ripple at the measured quantities of the microsource when this unit
is connected to the grid and the unbalance is created by the opening of one phase. In this case the
voltage unbalance measured at the terminals of the unit is of 2.82%. This is because of the stiff
Thevenin impedance of the utility system being in parallel to the unbalanced load at the source.
The oscillations on P and Q have a very low magnitude, while the oscillations on V have nearly
completely disappeared. This allows to conclude that the source does not require any active
action to compensate for negative sequences, as it has been shown that it can safely operate
under the voltage unbalances below the threshold of tripping.
70