Poster Presentation at the IEEE PES General Meeting. A feature of an Excitation Control System (ECS) for synchronous generators is to enable power system stabilization by providing an additional input to the Automatic Voltage Regulator (AVR) for external stabilization signals. This paper explores this feature by externally generating stabilization signals which are fed as an analog input to a commercial ECS. This allows bypassing the built-in PSS function in the ECS and gives more freedom to the end-user to utilize custom stabilizer models. ABB’s Unitrol 1020 Excitation Control System is coupled with Opal-RT’s eMEGAsim Real-Time simulator to perform Hardware-in-the-Loop simulation of the ECS. The output of several stabilizer models is fed to the ABB’s Unitrol 1020 ECS as external power system stabilization signals to analyze their performance for small signal stability enhancement.

1. RT-HIL Testing of an Excitation Control System for Oscillation Damping using External Stabilizing Signals
M. Shoaib Almas* and Dr. Luigi Vanfretti*~
*Electric Power Systems Division, KTH Royal Institute of Technology, Stockholm, Sweden, Email: {msalmas, luigiv}@kth.se
~R&D Department, Statnett SF, Oslo, Norway, Email: luigi.vanfretti@statnett.no
Utilization of external damping signals in a commercial ECS enables to utilize any local or wide-area measurement to
damp local or inter-area oscillation
· Excitation Control System (ECS) provides direct current to the synchronous machine field winding in order to regulate
the generator's terminal voltage.
· ECS also have integrated PSS functionality that provides adequate damping to the power system when small or large
disturbances may result in undamped oscillations in an interconnected power system.
· Different vendors have implemented different PSS types in their ECS unit to provide power system oscillation damping.
However, this restricts the end-user to rely on the built-in PSS algorithms and limited input signals for PSS.
Primary and Supplementary Functions of an Excitation Control System
ABB Unitrol 1020 Excitation Control System
Test Case Modeling and Real-Time Hardware-in-the-Loop Setup Conclusion
RT-HIL Assessment with External Damping Signals
· The PSS feature available in Unitrol 1020 ECS is
defined by the IEEE Std. 421.5-2005 PSS 2A/2B
model.
· The PSS2B has dual structures that use two signals
of angular velocity "ω " and power "P"
· In this study, external damping signals are
provided from different PSS and POD algorithms
(from Simulator) to the AVR of the ECS
Frequency
Calculation
Power
Calculation
Terminal
Voltage
Stator
Current
UM
IM
Washout
Filter
Lead-Lag
Compensator PSS Gain
Washout
Filter
Power
System
Stabilizer
(PSS)
f
V2
V1
Pe
ΔVPSS
To AVR
of ECS
External
Damping
Signals
Built-in PSS: Type IEEE PSS 2B
Klein-Rogers-Kundur's Power System showing only one
Area. Only generator G1 is equipped with Unitrol 1020
ECS
· Connection Diagram for interfacing Opal-RT with Unitrol
1020 ECS.
· The output of PSS/POD models being executed in real-
time in Opal-RT is fed to the ABB's Unitrol 1020 through
its analog input configured for receiving external damping
signals.
80 90 100 110
1.5
1.6
1.7
1.8
1.9
2
Rotor Field Current Input to Unitrol 1020 ECS
Time (sec)
FieldCurrent(pu)
80 90 100 110
0
1
2
3
4
Field Voltage Output from Unitrol 1020 ECS to Generator
Time (sec)
FieldVoltage(pu)
80 90 100 110
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
External Damping Signal Input to Unitrol 1020 ECS
Time (sec)
DampingSignal(pu)
80 90 100 110
400
450
500
550
Power Transfer from Area 1 to Area 2
Time (sec)
Power(MW)
No External PSS Signal
MB-PSS External Signal
dw-PSS External Signal
dPa-PSS External Signal
POD External Signal
· RT-HIL results show
that the external
damping signals
from different
stabilizer models can
be fed to the
commercial ECS to
provide adequate
damping.
· This liberates the
users from the
restriction of relying
only on the built-in
PSS implementation
of the ECS.
G2
Area 1
Local
Loads
900 MVA
900 MVA
900 MVA
20 kV / 230 kV
25 Km10 Km
900 MVA
20 kV / 230 kV
967 MW
100 MVAR (Inductive)
-387 MVAR (Capacitive)
Bus1
Voltage
Metering
Mechanical
Power (Pm)
Pm
Vfield
G1
Rotor
Field Current
TURBINE
PSS-MB
PSS-dω
PSS-dPa
POD
Stator
Current
Δ
Rotor Speed Deviation
ΔPa= Pm-Pe
Accelerating Power
ActivePower, PMU signals
Local/ RemoteSignals
Δ
Rotor Speed Deviation
Terminal
Voltage
External PSS
Damping Signals
Real-Time Simulation
(Executed within Opal-RT)
ABB Unitrol 1020 Executed
as RT-HIL