Presentation at the IEEE PES General Meeting 2015. 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
E-mail: msalmas@kth.se
Associate Professor, Docent
Electric Power Systems
Department
KTH Royal Institute of
Technology
Stockholm, Sweden
Special Advisor in
Strategy and Public
Affairs
R&D Department (FoU)
Statnett SF
Oslo, Norway
PhD Candidate
Electric Power Systems
Department
KTH Royal Institute of
Technology
Stockholm, Sweden
Dr. Luigi Vanfretti
E-mail: luigiv@kth.se
Paper No: 15PESGM1279

2. Background
One of the supplementary features of commercial Excitation Control Systems
(ECS) is to enable power oscillation damping through their built-in PSS
• Restricts the end-user to rely on the built-in PSS algorithms and limited
input signals for PSS.
– What did you do?
1. External damping signals are provided from different PSS and POD algorithms to the
AVR of the ECS (ABB Unitrol 1020)
2. Real-Time Hardware-in-the-Loop Simulation approach is used to explore the possibility
of power oscillation damping using external damping signals
– Expectation?
1. External damping signals based on local or wide-area measurements contain more
observability of the oscillatory mode.
2. Therefore, external signals can provide better damping as compared to the built-in PSS
models in PSS which rely on local measurements (mostly frequency and active power)
2

3. RT-HIL Setup
3

4. Results
• What did you discover/find out?
4
ABB Unitrol 1020 ECS is provided withe external damping signals from 4
different stabilizer models to provide oscillation damping
• Multi-Band PSS (IEEE type PSS4B PSS)
• Conventional Delta-ω PSS
• Acceleration Power PSS (IEEE type PSS 2A/2B)
• Phasor-based Power Oscillation Damping (POD) algorithm
80 90 100 110
1.5
1.6
1.7
1.8
Time (sec)
FieldCurre
80 90 100 110
0
1
2
Time (sec)
FieldVolta
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

5. Conclusions/Recommendations
• Conclusion
– The RT-HIL results have shown that the external damping signals from different stabilizer
models can be fed to the commercial ECS to provide adequate damping
– Thus liberating the users from the restriction of relying only on the built-in PSS
implementation of the ECS.
• Further Research
• Using different types of real PMU signals from an RT-HIL setup as input to an external
hardware-based stabilizer implementation
• Experimental proof of the theoretical results in previous publication.
• Noticeable Deviations from Expected Results
• Phasor based Power Oscillation Damping algorithm resulted in a slower response in
damping 0.64 Hz inter-area oscillation.
• Lower operational limits of hardware ECS to avoid any mis-operation
• Issues due to scalings which cannot be avoided and results in the small variation in the
field voltage output by Unitrol 1020 even in steady-state
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