Impact of Wind Fluctuations on Frequency Dynamics and Robust Control for Ensuring Frequency Specifications
Robust Control for Ensuring Frequency Specifications
Juhua Liu, Bruce Krogh, Marija
Juhua
Liu Bruce Krogh Marija Ilic
Electrical and Computer Engineering
Carnegie Mellon University
March 11, 2009
http://en.wikipedia.org/wiki/File:50Hz60Hz.svg
Accommodating Wind Generation
Accommodating Wind Generation
ƒ
ƒ
ƒ
ƒ
ƒ
Variability, Intermittency
Less forecast accuracy
In general not dispatchable
Reduces system inertia
y
Creates burden on the traditional p
plants to maintain system y
performance
http://windturbine‐corp.com
What is the impact
p
of wind g
generation on p
primary
y frequency
q
y
control (seconds to 1 min)?
2
Frequency Performance Specifications
Frequency Performance Specifications
ƒ Normal Conditions: 59.95Hz – 60.05Hz [1]
ƒ Load used as a resource
ƒ ERCOT threshold: 59.7Hz for 20 cycles
Under‐frequency
frequency load shedding (for contingency)
load shedding (for contingency)
ƒ Under
ƒ ERCOT threshold: 59.4Hz, shed 5% load
ƒ Future performance criteria may be different
[1] B. Kirby et al., Frequency Control Concerns In The North American Electric Power System, Dec 2002.
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Motivating Example
Motivating Example
[ ]
ƒ Modified WSCC 9‐Bus System[2]
[2] P. W. Sauer and M. A. Pai, Power System Dynamics and Stability. Prentice Hall, New Jersey, 1998.
4
50% Wind Penetration
50% Wind Penetration
ƒ Same amount of load; half of the traditional generation is replaced by wind generation
5
Load wind generation scenario
Load‐wind generation scenario
Power (MW)
350
300
Total Load Power
Total Load Power
250
200
150
Total Wind Power
100
50
0
0
2
4
6
8
10
12
Time (Sec)
14
16
18
20
6
Impact of Wind Generation
Impact of Wind Generation
Frequency
q
y ((Hz))
60 4
60.4
60.2
60
0% wind penetration
59.8
59.6
50% wind penetration
59.4
0
2
4
6
8
10
12
Time (Sec)
14
16
18
20
7
Robust Control for Frequency Regulation
Robust Control for Frequency Regulation
ƒ M
Measures must be taken to ensure frequency b
k
f
performance under normal conditions
ƒ
ƒ
ƒ
ƒ
storage
t
advanced wind turbine control
advanced traditional plant (governor) control
d
d di i
l l
(
)
l
demand response, etc.
ƒ Initial approach: Use H∞ control theory to design controllers for the traditional plants
ll f h
di i
l l
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The H∞ Approach
The H
ƒ Fi
Find a stabilizing controller K that
d t bili i
t ll K th t
minimizes the sensitivity from ‘w’
to ‘z’
to z
ƒ Advantages
ƒ
ƒ
ƒ
ƒ
satisfies performance specifications
p
p
optimizes tradeoff between performance and control effort
can easily incorporate model/parameter uncertainty
mature software for design
mature software for design
ƒ Disadvantage
can lead to high‐order
order controllers, but effective model controllers but effective model
ƒ can lead to high
reduction techniques exist
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2
bus Example
2‐bus Example
Wind Power (MW)
250
200
150
100
50
0
0
2
4
6
8
10
12
Time (Sec)
14
16
18
20
10
Traditional vs H∞ controllers
Traditional vs. H
Frequency (Hz)
60 4
60.4
60.2
60
With H inf
Controller
59.8
59.6
With Traditional
Governor
59.4
0
2
4
6
8
10
12
Time (Sec)
14
16
18
20
11
Mechanical Power
Mechanical Power
Mechanical Power (MW)
250
200
With H inf
Controller
150
With Traditional
With
Traditional
Governor
100
50
0
0
2
4
6
8
10
12
Time (Sec)
14
16
18
20
12
Current Research
Current Research
ƒ Decentralized control design
ƒ Investigation of alternative control actions
ƒ Demand response
ƒ Gas‐turbines
ƒ Storage devices
ƒ Coordination with load
Coordination with load‐frequency
frequency control (AGC)
control (AGC)
ƒ Implications for system frequency specifications
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Acknowledgments
ƒ Joint work with Professors Bruce Krogh and Marija Ilic
ƒ Supported by the National Science Foundation Information Technology Research (ITR) program, grant No. CNS‐0428404.
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