Wide-Area Stability Controls - Carson Taylor

8/15/2019 Wide-Area Stability Controls - Carson Taylor

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Wide-Area Stability Controls

Carson W. TaylorBonneville Power Administration (retired)

[email protected]

Wide Area Measurement, Monitoring and Controlin Power SystemsImperial College, London

16–17 March 2006


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Power System Stability Controls Local continuous feedback controls:

• Generator AVR/PSS, turbine governor

• SVC, other power electronic devices

Wide-area stability controls:

• Event-based or response (feedback) based• Continuous or discontinuous

• Angle stability or long-term voltage stability


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Power System Stability Controls

Δ y

response detection

switch capacitor/reactor banks

directdetection(SPS) trip generators/loads

Power System

Disturbances

Discontinuous

Controls

Power

SystemDynamics

ContinuousFeedback

Controls(generators)

Local and Wide-Area

(WACS)


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Event-Based Wide-Area Stability Controls

Emergency controls: Special Protection Systems(SPS)/Remedial Action Schemes (RAS)

Direct detection of pre-selected outages:• Signal to central logic, then signal to power plant or

substation for action• Generator/load tripping, reactive power compensation

switching

Many schemes in service, fast and reliable Complex: e.g., BPA 24/7 RAS dispatcher for arming

and supervision

Expensive (high redundancy required) Discontinuous control for pre-determined outages

only


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BPA Remedial Action Schemes (RAS)

Many schemes, many added after 8/10 Line loss detection logic on most 500-kV lines Generator tripping and/or 500-kV series/shunt

capacitor and reactor bank switching for singleline, 2 line, 3 line, 4 line outage combinations

Controlled islanding for Pacific ac intertie outage:• For outage signals sent to Colorado/New Mexico/Utah/Arizona to separate into north and south islands

PLC binary logic computers, including fault tolerant

two out three voting computers, redundant at twocontrol centers:• Transfer trip signals from line loss logic to control

centers, and from control centers to power plants andsubstations


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Western NorthAmericanInterconnection


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Example RAS Logic (one of many sheets)


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Wide-Area Response-Based Discontinuous

Controls BPA has one scheme for transient stability control

based on voltage magnitude measurements at a

Oregon–California border substation with transfertrip signals to nearby substations for seriescapacitor and shunt capacitor/reactor switching:

• Undervoltage relays and timers

“Wide-Area stability and voltage Control System”(WACS) described later


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Wide-Area Response-Based Discontinuous

Controls for Long-Term Voltage Stability Utilities have implemented wide-area response

based controls for voltage stability:

• Combination of voltage magnitudes and generatorreactive power or overexcitation limiter outputs atseveral locations

• Transfer trip or SCADA signals and binary logic

• Certain load level or generator MW output may berequired• Load tripping and capacitor/reactor bank switching• More sensitive and intelligent than local undervoltage

load shedding

BC Hydro, Entergy, TEPCO, Sydkraft, …


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Entergy Load Shedding in East Texas [1,2]

Source: Sharma Kolluri


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Discontinuous Wide-Area Stability Controls

(WACS) Response-based to stabilize large disturbances:

• First swing stabilization

• Reduce stress for improved damping• Establish post-disturbance equilibrium

Generator/load tripping, series capacitor and

shunt capacitor/reactor bank switching Single switching action, or

True feedback—observe response, take action,observe effect, take further action if necessary

SAFER than continuous control


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Continuous Wide-Area Stability Controls

BPA Pacific HVDC intertie early example [3,4]:• Remote input signal from ac intertie, multiple outputs• Analog sensors, communications, controller

• Digital control proposed but not accepted by management• In service 1976 – late 1980s

Design based on system transfer functionmeasurement (bode plots) rather than simulation:• AC intertie power or current used for input; for two area

system, signal is proportional to rotor angle difference• Current transducer was diode three-phase bridge rectifier

with 360 Hz notch filter and 40 Hz low pass filters—verysimple and fast!

• Later work indicated ac intertie apparent resistance lessprone to NMP behavior [7]


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Negatively Damped Oscillation, 2 August 1974

P O W E R

I N M W

10080 12060400 20

1400

1600

1700

1500

1800

TIME IN SECONDS

jfh

Time - seconds

A C I n t e r t i e p

o w e r - M W


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Pacific HVDC Intertie Modulation


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Pacific HVDC Intertie Modulation

60-Hz Notch 120-Hz Notch Low pass


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Western NorthAmericanInterconnection

Pacific HVDC Intertie

Modulation


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Continuous Wide-Area Stability Controls

Difficult and DANGEROUS:• Especially for HVDC, TCSC, SVC

• Sensor speed versus filtering, including anti-aliasing filtering• Latencies (pure time delays) in digital sensors, communication,

and control— unlimited phase lag for high frequencies


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Signal Delay - PMU to Controller (Ken Martin) Combined communications time delay: PMU to PDC

to PDC PDC adds 5-6 ms

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

50

51

52

53

54

55

56

57

58

59Delay - Slat/BE230 PMUs

M i l l i s e c o n d s

Data Points

Async interface to Sonet53 ms overall Direct async into Sonet24 ms overall

0 10 20 30 40 50 60 70 80 90 100

21.5

22

22.5

23

23.5

24

24.5

25

25.5Delay - Slatt PMU, sample 1300-1400

M

i l l l i s e c o n d s

Data Points

Source: Ken Martin


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CONTROL

LAW controller input ym(t)

load noise uL(t)

external inputs uE(t) unmeasured response y'(t)

input u(t)measured response y(t)

extraneousinputs

measurement

noise

nonlinear interactions

ACTUATOR

Sensors&

Transducers

POWER

SYSTEM

Operating Environment for Feedback Control

linear response

nonlinear response

actuator noise

command

Source: John Hauer


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Impediments to Wide-Area Damping Control

(Dr. John Hauer) Dynamics mimicking interarea oscillations

• RMS sensor processing artifacts

• Network resonances and harmonics, hydraulic oscillations

Abrupt changes in system structure

Intermittent nonminimum-phase behavior

Sparse monitoring of controller effects

Models not sufficiently realistic

High potential for adverse controller interactions


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jfh

MEXICO

SUNDANCE

KEMANO

MICA

COLSTRIP

PALO

VERDE

HOOVER

GRAND

COULEE

MEADFOUR

CORNERS

SHASTA

Major interaction path

"Index" generator

Key Interactions & Index Machines forWestern Power System Dynamics

Western North America Oscillatory Dynamics

Source: John Hauer


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Digital Sensors/Communications in Wide-

Area Control (Hauer) Communication delays (latencies) range from 20 to

100 ms

PMU, controller, output communications latencies? Pure time delays can be lethal source of instability

in feedback controls:• Delay of 50 ms causes 180° of phase lag at 10 Hz, 45° at

2.5 Hz• 45° of uncompensated lag annihilates the 45° of phase

margin typically required in feedback control.Compensate lag or reduce controller bandwidth (and

performance)• Latency cannot be exactly compensated

General issue: Digital networks suitable forfeedback control?


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On the other hand …


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Response-Based Wide-Area Stability Controls

Facilitated by IT:• Digital sensors, communications, controllers• Fiber optic communications

Greater observability and controllability

Time delays/latencies pose challenges:• But control feasible for interarea oscillations

Example—low frequency mode with 3 second period:• Need first swing stabilization

• Impulse (short circuit) response peak at 0.75 second• Step (line/generator outage) response peak at 1.5 second• 50 ms latency causes 6° lag at 0.33 Hz

WACS examples later


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Step Response of Second Order System


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Wide-Area Continuous Stability Controls

Several organizations have investigated wide-areacontrols: universities, ABB, Hydro Quebec, ….

• “Wide-area PSS” (power system stabilizer)• PSS applied to generators, synchronous condensers, SVCs,TCSCs, etc.

Work of Innocent Kamwa and colleagues at Hydro

Quebec notable [5,6]:• “Overall, wide-area control is consistently three to 20times more efficient technically than the competing localcontrol…” [6]

• “More efficient” implies lower gain needed than for localcontrol

• Voltage phase angles from PMUs used as inputs• Fuzzy logic PSS with inputs θ , dθ /dt


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Future of Digital Controls

Many digital controls based on traditionalcontinuous analog control concepts

Discontinuous controls have advantages:• Control deadband, or detection of need for control• Control mode shifting, e.g., small signal damping mode

versus large signal transient stability stabilization mode• PLL techniques [8]• Walk before run

Heuristics (HNN) versus theoretical approaches:• Heuristic approaches for large-scale, large disturbance,

nonlinear systems?• Complementary approaches including AI


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References

1. S. Kolluri and T. He, “Design and Operating Experience with Fast Acting Load Shedding Scheme in the

Entergy System to Prevent Voltage Collapse,” Proceedings of IEEE/PES 2004 General Meeting.

2. S. Kolluri, K. Tinnium and M. Stephens, “Design and Operating Experience with Fast Acting Load

Shedding Scheme in the Entergy System to Prevent Voltage Collapse,” Proceedings of IEEE/PES 2000

Winter Meeting.3. R. L. Cresap, D. N. Scott, W. A. Mittelstadt, and C. W. Taylor, “Damping of Pacific AC Intertie Oscillations

via Modulation of the Parallel Pacific HVDC Intertie,” CIGRE 14-05, 1978.

4. R. L. Cresap, D. N. Scott, W. A. Mittelstadt, and C. W. Taylor, “Operating Experience with Modulation of

the Pacific HVDC Intertie,” IEEE Transactions on Power Apparatus and Systems, Vol. PAS-98, pp. 1053–

1059, July/August 1978.

5. I. Kamwa, R. Grondin, and Y. Hebert, “Wide-area measurement based stabilizing control of large power

systems-a decentralized/hierarchical approach,” IEEE Transactions on Power Systems, Vol. 16, No. 1,pp. 136–153, February 2001.

6. I. Kamwa, A. Heniche, G. Trudel, M. Dobrescu, R. Grondin, and D. Lefebvre, “Assessing the Technical

Value of FACTS-Based Wide-Area Damping Control Loops,” Proceedings of IEEE/PES 2005 General

Meeting.

7. J. F. Hauer, “Reactive Power Control as a Means for Enhanced Interarea Damping in the Western U.S.

Power System—a Frequency-Domain Perspective Considering Robustness Needs,” Application of Static

Var Systems for System Dynamic Performance, IEEE/PES 87TH0187-5-PWR.8. C. Gama, “Brazilian North–South Interconnection — Control Application and Operating Experience with a

TCSC,” Proceedings of 1999 IEEE/PES Summer Meeting, July 1999.


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Wide-Area Stability Controls - Carson Taylor