Control and Operation of islanded AC microgrid

Full description

There are basically two kinds of line faults that occur in the conventional power system. (i) Symmetrical and (ii) unsymmetrical faults. Out of the line faults, LLL (Line-Line-Line) fault is considered as symmetrical and the rest such as LG (Line-Ground), LL (Line-Line), and LLG (Line-Line-Ground) are considered as unsymmetrical faults. The percentage of occurrence of each fault in a power system transmission line is shown in Figure 3.

In islanded microgrid also, the micro-sources are connected to load through distribution lines (single/three phases). So, the occurrence of the fault on these lines might be a possibility. The occurrence of these faults may lead to frequency and voltage instability issues as there is no support from the utility grid. An early identification of these faults would help resolve such issues.

For each type of line fault, the load current was simulated before fault, during fault and post-fault. The plots are shown in Figure 4. A clear transition and magnitude variation can be observed during the fault duration. For some of the line faults, the magnitude is found to be more while for others it is less. This magnitude depends on the impedance (positive, negative and zero sequences) calculated from the corresponding sequence networks in each fault case. Here, the load current is observed to be more for LG and LLG faults, compared to LL and LLL faults. However, a clear distinction between the faults cannot be identified with just plotting the fault currents

Notes

Use of MATLAB/SIMULINK