ABB UNITROL 1020 - Page 81

 Chapter 3 - Device Overview
UNITROL 1020 User Manual 3BHS335648 E82 73

+
Ks3

+
+
-
USTmax
USTmin
1
1
4
3


sT
sT
1
1
2
1


sT
sT
1
1
11
10


sT
sT
1S
K
1
1
1

W
W
sT
sT
2
2
1
W
W
sT
sT 
3
3
1
W
W
sT
sT 
4
4
1
W
W
sT
sT 
2
7
1
S
K
sT 
8
9
1
( 1)
N
M
sT
sT





PID
(AUTO)
VSTmax
VSTmin
UST_PWM
Lead lag injection
Scaling: ±0.1% to ±1.0%
WASH-OUTS
Delta P
Integrator
RAMP-TRACKING
Filter
PSS-Gain
LEAD-LAGS
+

+
+
Frequency injection
Scaling: ±0.1% to ±1.0%
Synthesized
rotor speed ω
[delta pu]
Power
P [delta pu]

+
+
Power injection
Scaling: ±1.0% to ±10.0%
TP
+
TP
+
TP
+
TP
+
TP
TP
+
TP
+
TP TP
TP
TP
TPTP
TP
TP
PSS TP output 1: Free configurable (blue dots)
PSS TP ouptut 2: Free configurable (blue dots)
Remark:
Settings of PID are interlinked to AUTO-PID (Voltage regulator)
UST_PWM is added to the AVR output
1
1
13
12


sT
sT
Figure 3-17 PSS model.
Figure 3-18 shows a simplified diagram of the PSS and related functions
V1
V2
Frequency
Calc
Power
Calc
U
M
I
M2
PSS
PSS
f
Pe
Figure 3-18. Simplified diagram of PSS.
The frequency input is based on synthesized frequency measurement taking into account
terminal voltage as well as machine current.
Due to the PSS function implementation and structure of UNITROL 1020 AVR, there are
some points to be noticed when using this PSS. The following elements limit the
maximum performance of the PSS:
 Brushless excitation system,
 Positive field voltage (only) can be supplied.
PSS Parameters
The PSS function can be activated by the PSS_SELECT configuration and by digital input
or over Modbus.
If digital input “PSS Enable” is activated, PSS activation only depends on the status of the
digital input. Otherwise PSS activation is defined by the parameter PSS-Select or the
Modbus control bit.
PSS is blocked in case the machine voltage is below 0.8 p.u., above 1.2 p.u. or active
power is below the defined threshold. In addition, the PSS can be blocked by configurable
frequency gradients.
The PSS feature is only functional if the PSS SW Option is released on the unit.
The PSS signal comes either from the internal PSS or from the analog input ‘External
PSS’. The switch is controlled by a checkbox in the PSS setup.
When the switch is set to external PSS, the internal PSS calculation can be skipped.