Page 51 - Energize May 2022

TECHNICAL

Figure 7: 3D chart of nodal voltage changes when battery is discharging at Figure 9: 3D chart of nodal voltage changes when battery is charging at
300 kW in island mode at selected locations 400 kW in grid-connect mode at selected locations

Figure 8: Average changes per node when battery is discharging at 300 kW Figure 10: Average changes per node when battery is charging at 400 kW in
in island mode at selected four locations grid-connected mode at selected four locations

Charging at 400 kW for a high voltage scenario in grid- defined and calculated to illustrate the voltage performance and
connected mode storage effectiveness for 24-hour operation.
A 400 kW charging scenario is tested in grid-connected mode.
The objective of this test is to evaluate the ability of decreasing • Number of high voltage violations (HVV) during a 24-hour period.
system voltages by charging the battery so that a higher A high voltage violation is defined as voltage above 1,05 p.u. that
renewable penetration can be achieved in a light load condition. remains above this value before the system controls react to set it
The procedure is similar to Case A. Figure 9 shows that all 26 down.
three-phase bus voltages change when a battery is placed at four • Number of low voltage violations (LVV) during a 24-hour period. A
selected locations charging at 400 kW. Again, location I exhibits the low voltage violation is defined as the decrease of voltage below
lowest decrease in voltage throughout the three-phase nodes of 0,92 p.u. that remains below this value before the system controls
the system. Also, as expected from the voltage sensitivity analysis, react to push it up.
the effects of charging a battery placed at locations II, III and IV • Time duration for HVV and LVV during a 24-hour period. Time in
are much higher. In order to quantify the effect per node, an minutes where the voltage stays above 1,05 p.u. and below 0,92 p.u.
arithmetical average is computed. The result is shown in Figure 10. • Index of storage charging effectiveness (SCE)

Real-time scenario
From Cases A and B, one can conclude that locations II, III, and IV are
the best potential candidates. However, these two tests are steady • Index of storage discharging effectiveness (SDE)
state analysis. It is necessary to run a time sequence simulation to
evaluate and find out which location is the most effective for system
voltage management. Therefore, a more realistic simulation has
been done in this case by importing a typical daily wind profile and
a typical sunny solar irradiation profile for the city of Milwaukee into The results of these five indexes are shown in Table 3. It is worth
the complete system model in PSCAD. noticing that location III is not a valid place to install energy storage
A 24-hour simulation was run for all four locations. The power devices, because on the same bus there is 750 kW wind power
management and controls, as well as load shedding criteria, generation, and the parallel of two generations without any impedance
have been stated in [9]. The following energy quality indexes are inbetween causes a dramatic voltage variation during transient.
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