Impact of Drivetrain on Wind Farm VAR Control - Upwind

UPWIND
Magnitude (dB)
Phase (deg)
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
0
-45
-90
-135
10 -2
-180
10 -1
10 0
Bode Diagram
Frequency (rad/sec)
Figure 4-3. Closed loop Bode diagram <strong>of</strong> the static excitation system.
The excitation system performance was examined by switching a capacitive load impedance
at the POI at Bus 1 <strong>of</strong> the considered test system in this report. This was performed with
different system SCRs. The capacitive impedances were 0.5, 2 and 3.5 pu based on an
arbitrary 100 MVA base with system SCRs <strong>of</strong> 20, 5, and 3 respectively to have almost the
same step voltage change at the POI, and at the same time having the excitation system
operating within the limits <strong>of</strong> its field voltage. Two different cases <strong>of</strong> wind farm power levels
were considered. The first one was full power with all WTGs in service, and the second one
was half power with half <strong>of</strong> the WTGs in service. The system response is shown in Figure 4-4
for full power and in Figure 4-5 for the half power case. The left plots depict the WTG
terminal voltage (blue line) and field voltage (red line) as well as the POI voltage (green
line). The right plots show the WTG active (blue line) and reactive power (red line).
It can be inferred how the excitation system could provide a smooth response in regulating
the WTG terminal voltage with a rough time constant <strong>of</strong> 2 seconds for system SCR <strong>of</strong> 20 and
about 1 second for systems SCRs <strong>of</strong> 5 and 3. With half <strong>of</strong> the WTGs in service, the excitation
time response is a little bit longer than that in the case with all WTGs in service. However,
the difference is not noticeable. This shows that the system SCR has a more pronounced
impact on the excitation system than that due to the number <strong>of</strong> connected WTGs.
Deliverable D5.9.1 33
10 1
10 2
10 3