PSERC
Real Time Control of Power Grids
Anjan Bose
Kevin Tomsovic
Mani Venkatasubramanian
Washington State University
Pacific Gas & Electric Co.
June 20, 2003
PSERC
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Control of the Power Grid
PSERC
• Load Following – Frequency Control
• Area-wise
• Slow (secs)
• Voltage Control
• Local
• Slow to fast
• Protection
• Local (but remote tripping possible)
• Fast
• Stability Control
• Local machine stabilizers
• Remote special protection schemes
• Fast
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Communication for Power System
PSERC
Third Party
•Analog measurements
•Digital states
Control Center
RTU
RTU
RTU
Monitoring the Power Grid
PSERC
• Alarms
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•
•
•
Check for overloaded lines
Check for out-of-limit voltages
Loss of equipment (lines, generators, feeders)
Loss of communication channels
• State estimator
• Security alerts
• Contingencies (loading, voltage, dynamic limits)
• Corrective or preventive actions
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Substation Automation
PSERC
• Many substations have
•
•
•
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Data acquisition systems at faster rates
Intelligent electronic devices (IED)
Coordinated protection and control systems
Remote setting capabilities
• Data can be time-stamped by satellite
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Evolution of Communication
System
Control Center
RTU
RTU
PSERC
•Utilizing existing system
•Building a new one
RTU
Networks
Communication for Power System
(future)
Control Center
Substation
Substation
Networks
Third Party
Substation
PSERC
WSU Real Time Control Project
PSERC
• Study feasibility of different levels of area-wide
real time controls for the restructured power
system
• Slow controls
• Automatic Generation Control (AGC)
• Voltage control
• Adapting special protective schemes (SPS) or
remedial action schemes (RAS) for stability
• Real time stability control using soft-computing –
neural networks, pattern recognition, etc.
• Real time stability control (the holy grail)
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Slow Controls
PSERC
• Load Frequency Control (Load Following)
• Present method adequate
• Single-buyer or Bilateral
• Who pays for control performance?
• Voltage Control
• Only local control in No America
• Do we need area-wide control?
• Again, who pays?
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Example System - AGC
PSERC
20s delay
CA1
G2
CA2
G1
G3
20s delay
G4
CA3
10s, 0.1pu load deviation
50s delay
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Example AGC Results
PSERC
Simulations for three control areas various configurations
S c e n a rio
T ra d itio n a l A G C
B ila te ra l
M ix e d A G C a n d
B ila te ra l
U n s ta b le in
c e rta in s itu a tio n s
w ith ra n d o m
d e la y in a ll
Random
d e la y
g e n e ra to rs .
N o a d v e rs e
a ffe c ts fro m
F a il to m e e t
c u s to m e r
demand and
m ay becom e
u n s ta b le .
S y s te m n o t a d v e rs e ly
a ffe c te d if in b ila te ra l
u n its o n ly b u t th o s e
p a rtie s c a n n o t m e e t
th e c o n tra c tu a l
s c h e d u le .
ra n d o m d e la y in
s in g le g e n e ra to r.
B o th fix e d
and
ra n d o m
d e la ys
S y s te m m a y b e c o m e
--
--
u n s ta b le fo r s h o rt
d e la y s .
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Area Voltage Control Framework
PSERC
MEASUREMENTS
EMS
SCADA
DEVICE
SWITCHING
STATUS
SLOW
COMMANDS
ALARMS
VOLTAGE
STATE
ESTIMATOR
MODEL
OPERATOR
CONTROLLER
STATE
ALARMS
LOAD
FOECASTING
LOAD
TREND
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New scheme for Voltage Control
PSERC
An automatic voltage control scheme would
dynamically manage the reactive power available in
a certain geographic region called Voltage Control
Area (VCA).
A local ancillary service market for reactive power
can consequently be developed in that specific
VCA, granted that generation-based voltage control
is the only voltage control recognized as an
ancillary service by NERC.
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IEEE 39bus system divided in VCAs
PSERC
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RAS/SPS
PSERC
• Present Day State-of-the-Art
•
•
•
•
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Hard-wired
Parameters set by off-line studies
Armed in real time according to system condition
Mainly activates switching (circuit breakers)
Can activate FACTS controllers
• Possibilities
• Soft-wired (set according to system condition)
• Parameters set by on-line computation
• Continuous control
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Real Time Control for Stability
PSERC
• Oscillatory Stability
• Number of modes finite and detectable
• Possible control in hundreds of ms
• Possible area-wide control of system stabilizers
• Transient Stability
• Control needed in tens of ms
• Fast detection is difficult
• Soft-computing
• Use ANNs, pattern recognizers, etc instead of modelbased computation
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Oscillation Damping Controller
PSERC
PSDC STATUS
From From
Area 1 Area 2
From
Area n
EXTERNAL
TRIGGERS
WIDE AREA
MEASUREMENTS
Multi-input
Prony Analysis
INTERAREA
FFT Analysis
AND LOCAL
MODES
To Area 1
Trigger
Coordination
To Area 2
To Area n
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Proportional Voltage Controller
PSERC
• Real-time switching of remote
generation, shunt and series capacitor
banks coordinated by the controller.
• Control actions typically during the first
swing of large disturbances.
• Improved version of the controller being
implemented at BPA – Wide Area
Control System.
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Some Research Issues
PSERC
• Theoretical basis for control issues that
incorporate communication and computation
• Simulation tools that incorporate control,
communication and computation
• What is a reasonable framework of the
communication system for the power grid
• What controllers (FACTS) will be readily
available to consider in such wide-area control
• We should be ready with practical control
schemes in anticipation of the technology
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