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TECHNICAL

Location Bus No. Index II Index IV Units
I 828 0.15 0.062 rad / p.u. power
II 862 0.22 0.0675 p.u. volts / p.u. power
III 848 0.22 0.0675 rad / p.u. R1 power
IV 858 0.215 0.0663 p.u. volts / p.u. R1 power
Table 2: Values of index II and IV for nominal loading condition

solar PV, energy storage devices and diesel generators. The main
advantage of using PSCAD is that a real-time simulation result can
be obtained to assess the effects of storage in different locations
with consideration to the controls and operations of the system.
The microgrid operation was tested and analysed in four
Figure 4: Curve of index II for four locations in the microgrid different operation modes, defined as island mode, grid-
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connected mode, transition from grid-connected to island
mode, and transition from island mode to grid-connected mode.
Each one of these modes has its own power quality issues that
affect the stability of the system, and primarily the voltage
stability. Discharging at 300 kW for a low voltage scenario in
island mode First, a 300 kW discharging for energy storage
system at four locations in island mode is studied. The one-
line diagram of the microgrid and four candidate locations are
shown in Figure 6.
A 1,4 MW nominal load is considered during simulation. No
renewable generations are providing power to the system, as this
test focuses on a low voltage scenario. A 500 kW ZBB battery,
equipped with an inverter, interfaces to the microgrid at four
Figure 5: Curve of index IV for four locations in the microgrid
different locations. The voltage values are monitored across all
three-phase buses of the system, before and after the battery is
According to Index II, as shown in Figure 4, the average discharged. These voltage results are captured once the steady
voltage changes per MW at four locations follow the curve in state has been achieved. Figure 7 shows the three-phase average
different system loading conditions. Obviously, locations II and IV voltage change per unit, when the battery is discharging at 300
are the best. The same results are observed for Index IV in Figure kW (60% of the rated power). From the three-dimensional figure,
5. By comparing Indices II and IV, one can easily find and conclude it can be observed that location I has the lowest increase in
that active power has a bigger impact on voltage magnitude voltage throughout all buses. Locations II, III and IV have a bigger
than reactive power in the proposed microgrid. This is caused increase in voltage as the battery is discharged.
by a significant resistance component in the cable used in the Locations II, III and IV have similar performances. An average
microgrid. For instance, the impedance of a commonly used cable of all bus voltage changes is computed to determine which
in the system is 1,93+j1.41 ohm/mile. The values of Indices II and location is better and more effective. The results are shown and
IV for nominal loading condition are given in Table 2. compared in Figure 8, where locations II and IV are the best
One of the main consequences of finding possible candidates choices.
for the storage location by using the proposed methodology
opens the possibility of determining which possible locations for
storage placement are in larger systems, and as the microgrid
concept expands upstream in the system.

Results from modelling the case in PSCAD
In order to examine and evaluate the selected candidates
obtained from the proposed methodology, various simulations
and tests are conducted. The system is modelled in PSCAD.
The detailed system configuration and transmission line
information are described in [7 to 9]. The model offers a
7-9
wide variety of detailed models, such as voltage regulators,
unbalanced transmission lines, different types of loads, and
various generations and their controls, including wind power, Figure 6: One-line diagram of the microgrid with four selected locations

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