Abb Power System Voltage Stability

Test Case: Power System Voltage Stability Mats Larsson

ABB Corporate Research Mats Larsson / 2002-02-18 / 1

 2002 ABB Corporate Research Ltd, Baden, Switzerland

Preview
The People from ABB


Characteristics of Power Systems
Voltage Stability


Corrective Measures


The ABB Platform for Corrective Control
What do we need from CC ?


The ABB Power Grid Test Case
Conclusion

ABB Corporate Research Mats Larsson / 07.10.2001 / 2

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

People Involved From ABB


Eduardo Gallestey




Mats Larsson




PhD in Mathemathics 1998




PhD Industrial Automation 2001

ABB


University of Bremen
Lund University
Optimal and robust control,
Control and stability of power  2001 ABB Corporate Research Ltd, Baden, Switzerland Corporate Research optimization etc. systems

Mats Larsson / 07.10.2001 / 3

ABB

Characteristics of Power Systems









Large-scale Substantial nonlinearity Wide span of time-scales Uncertainty Changing operating point Mix of continuous and discrete control variables Embedded Controllers System model has differentialalgebraic structure


A good example of a ”complex” system !

ABB Corporate Research Mats Larsson / 07.10.2001 / 4

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Control of Power Systems



Global control problem extremely difficult Decomposition, Controller hierarchies




Some stability concerns in PS





Frequency stability – Simple linear decentralized control Transient stability -- Energy functions, Lyapunov Small-disturbance stability – Linear analysis, H_inf etc. Voltage stability – Model Predictive Control etc.

ABB Corporate Research Mats Larsson / 07.10.2001 / 5

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

System collapse due to Voltage Instability Date

Location

Time to Collapse

860413

Winnipeg, Canada, Nelson River HVDC link

1s

861130

SE Brazil, Paraguay, Itaipu HVDC link

2s

850517

S Florida, USA

4s

870822

W Tennessee, USA

10 s

960702

Western USA

35 s

831227

Sweden

55 s

820902

Florida, USA

1-3 min

821126

Florida, USA

1-3 min

821228

Florida, USA

1-3 min

821230

Florida, USA

1-3 min

770922

Jacksonville, Florida

minutes

820804

Belgium

4-5 min

870112

Western France

6-7 min

651209

Bretagne, France

minutes

761110

Bretagne, France

minutes

870723

Tokyo, Japan

20 min

781219 France Research ABB Corporate Mats Larsson / 07.10.2001 / 6

700822

Japan

26Switzerland min  2001 ABB Corporate Research Ltd, Baden, 30 min

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Voltage Stability 1 p.u

j1

j1 p.u. =>

I + VL

1

R

−

R 1 1 ⇒ VL = RI = = R + j1 R + j1 1 + jg 1 v = VL = 1+ g 2 I=

1

v

v = load voltage p = load power g = load admittance

g↑

vcrit

p = gv 2 pmax


Maximum transfer: p = pmax at v = vcrit  2001 ABB Corporate Research Ltd, Baden, Switzerland ABB Corporate Research Mats Larsson / 07.10.2001 / 7

p

ABB

Stability analyis
Load constant power behavior:

 dg 2 = − p gv T 0  dt   1 v =  1+ g 2

(increase g if consumption too low)


Stationary points given by: f ( g ) = 0 => g * =

v

1 1 ± −1 2 2 p0 4 p0

=>

f (g) =

g dg 1 = ( p0 − ) dt T 1+ g 2

p0 < 0.5 - two equilibrium points p0 = 0.5 - the two equilibrium points coalesce

p0 > 0.5 - no equilibrium points

g↑

vcrit

p

p0 Research pmax ABB Corporate Mats Larsson / 07.10.2001 / 8

Unstable if: p0 > pmax or v < vcrit  2001 ABB Corporate Research Ltd, Baden, Switzerland

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Simulation Results


Small Step in p0 (a) – stable case, (b) unstable case

ABB Corporate Research Mats Larsson / 07.10.2001 / 9

 2001 ABB Corporate Research Ltd, Baden, Switzerland

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Tap Changer Control

R

transmission

generation

130/50 kV

R

50/20 kV

130 kV Voltage




50 kV Voltage

1.08 1.04 1 0.96

0

6

12

ABB Corporate Research Mats Larsson / 07.10.2001 / 10

18

24 hours

R

20/10 kV





Used to control customer voltage Relay control Time delay + Deadband





Uses a local viewpoint Bad for System Stability !

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Generator Overload Limits
Generators normally under terminal voltage control


If the generator is overloaded, voltage control is lost

1.05

Tap Controlled Load

Generator Voltage

Overload limit reached

1

0.95 Tap Changer Control

0.9 0 100 ABB Corporate Research Mats Larsson / 07.10.2001 / 11

200

300

400

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Typical Instability Scenario 1. 2. 3. 4.

Line or generator outage reduces the voltage in an area Temporary load reduction Transfer capacity to the area is reduced Load demand recovers (distribution voltage control, inherent dynamics) 5. Voltage is further reduced 6. Generator overload protection activated 7. Collapse ! Time scale: seconds to several minutes

ABB Corporate Research Mats Larsson / 07.10.2001 / 12

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Countermeasures against Voltage Instability

Time (seconds)







Load shedding Tap locking Capacitor switching Generator voltage setpoints

ABB Corporate Research Mats Larsson / 07.10.2001 / 13

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Countermeasures (ctd.)

ABB Corporate Research Mats Larsson / 07.10.2001 / 14

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Wide-area Protection GPS Satellite

SPC PMU

WAN

Transmission Network

PMU




PMU

PMU

PMU

Snapshot of power system topology and state every 50-250 ms


Sophisticated control possible  2001 ABB Corporate Research Ltd, Baden, Switzerland ABB Corporate Research Mats Larsson / 07.10.2001 / 15

ABB

The ABB Power Grid Test Case
Small-scale example
Discrete Step Controls
Tap locking


Load Shedding


Capacitor Switching


Hybrid Behaviour


Generator overload protection
Transformer Relay Control

ABB Corporate Research Mats Larsson / 07.10.2001 / 16

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Collapse Scenario


Line tripping (L3) after 100 s





1.05

Inherent Load Recovery Tap Changer Tries to Restore Voltage Generator field limit activated at 286 s Collapse

Tap Controlled Load

Generator Voltage

Overload limit reached

1 0.95 Tap Changer

0.9

0 100 ABB Corporate Research Mats Larsson / 07.10.2001 / 17

Control

200

300

400

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

What Do We Need from CC ?


Optimal Control Problem




Observability Analysis




Controllability




Reachability Analysis


Find optimal switching sequences for our controls


Select a minimum but sufficient number of measurement points


Select a minimum but sufficient number of control points


Which are the safe operating regions ?
When is the last time to stabilize the system, given some set of available controls ?


.... and other things ? ABB Corporate Research Mats Larsson / 07.10.2001 / 18

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB

Conclusion


Industrially highly relevant problem




We are dealing with transmission – not distribution




A challenging test case:


Nonlinearity
Load behaviour is uncertain
Hybrid behaviour
Embedded relay controls
Limiter logic


Large Scale




Present Status




Later on, medium and large scale examples will be available


Now available in Modelica language, SIMULINK SimStruc
T. Geyer at ETH currently works on a PWA model

ABB Corporate Research Mats Larsson / 07.10.2001 / 19

 2001 ABB Corporate Research Ltd, Baden, Switzerland

ABB