RT-HIL Testing of an Excitation Control System for Oscillation Damping using External Stabilizing SignalsM. 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

PowerSystem

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 1101.5

1.6

1.7

1.8

1.9

2

Rotor Field Current Input to Unitrol 1020 ECS

Time (sec)

Fie

ld C

urr

en

t (p

u)

80 90 100 1100

1

2

3

4

Field Voltage Output from Unitrol 1020 ECS to Generator

Time (sec)

Fie

ld V

olt

ag

e (

pu

)

80 90 100 110-0.04

-0.03

-0.02

-0.01

0

0.01

0.02External Damping Signal Input to Unitrol 1020 ECS

Time (sec)

Dam

pin

g S

ign

al (p

u)

80 90 100 110

400

450

500

550Power Transfer from Area 1 to Area 2

Time (sec)

Po

wer

(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 MVA20 kV / 230 kV

25 Km 10 Km

900 MVA20 kV / 230 kV

967 MW100 MVAR (Inductive)

-387 MVAR (Capacitive )

Bus1

Voltage Metering

MechanicalPower (Pm)

Pm

Vfield

G1Rotor

Field Current

TURBINE

PSS-MB

PSS-dω

PSS-dPa

POD

Stator Current

Δ Rotor Speed Deviation

ΔPa= Pm-PeAccelerating Power

Active Power, PMU signalsLocal / Remote Signals

Δ Rotor Speed Deviation

Terminal Voltage

External PSS Damping Signals

Real-Time Simulation

(Executed within Opal-RT)

ABB Unitrol 1020 Executed

as RT-HIL