power control agc1
TRANSCRIPT
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC)
1
Power System Control and Operation:
Automatic Generation Control (AGC)
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 2
Outline
Read chapter 11: 11.0-11.6.
Homework: 11.2, 11.6
Automatic Generation Control (AGC)
System modeling: control block diagram
AGC for single generator
AGC for 2 generators
AGC for multi generators
Area Control Error (ACE)
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 3
Purpose of AGC
To maintain power balance in the system.
Make sure that operating limits are not
exceeded:-
Generators limit
Tie-lines limit
Make sure that system frequency is constant
(not change by load).
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 4
Overview of AGC
Load is always changing.
To maintain power balance, generators need to
produce more or less to keep up with the load.
When Gen < Load (Gen > Load), generatorspeed and frequency will drop (rise).
=> We use this generator speed and frequency
as control signals!
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 5
3 Components of AGC
Primary control
Immediate (automatic) action to sudden change of load.
For example, reaction to frequency change.
Secondary control
To bring tie-line flows to scheduled.
Corrective actions are done by operators.
Economic dispatch
Make sure that the units are scheduled in the most economical
way.
This presentation covers only primary and secondary
control of AGC.
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 6
AGC for Single Area
System Modeling
Single Generator
Multi Generators, special case: two
generators
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 7
System Modeling: Turbine-Governor Model
Small signal analysis model, relating mechanical powerto the control power and the generator speed.
Where = Small change in control setting power
= Small change in governor synchronous speed
= Small change in mechanical output power
= Regulation constant
= Transfer function relating mechanical power to control signals
CP MP
TG
sTsT 11
1
sGM
R
1
+
-
C
P
MP
sGM
R
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 8
Speed-Power Relationship
From synchronous turbine-governor: small
signal analysis model,
At steady state (s 0, 1), we have
RPsGPCMM
1
R
PPCM
1
sGM
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 9
Static Speed-Power Curve
From,
Primary control: Immediate
change corresponding tosudden change of load
(frequency)
Secondary control: Change in
setting control power to
maintain operating frequency. The higher R (regulation), the
better.
R
PPCM
1
Slope = -R
1MP 2MP1CP 2CP
MP
= =
1
2
0
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 10
System Modeling: Generator Model
This model relates mechanical power to power
angle, ignore change of voltage.
Note that power angle is not voltage angle ( )
TDsMs 21
MP
G iiV +
-ii
E
sjX iiV
ii
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 11
AGC for Single Generator
Since , we can draw
closed loop power control system as below. 0
CP
TG sTsT 11
1
R
1
+
-
TDsMs 2
1MP
s
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 12
AGC for Multi Generators
Consider effect of
power flows in transmission lines, and
loads at each bus
to mechanical power of each generator. This analysis assumes that every bus is a
generator bus.
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 13
Power Balance Equation at Each Bus
At each bus,
Where = Generator i power
= Load power at bus I
= Power flow from bus i
Consider small changes,
iDiGi PPP
GiP
DiP
iP
iDiGi PPP
2GP
G1 G2
1GP
3DP
1DP
2V
1V
3V
G3
2DP
3GP
2P1P
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 14
Load Power Equation ( )
Assume that
Where = Small change of load input
= Small change of load power
= Small change of voltage angle
Substitute in power balance equation,
We have
LiiLiLiiLiDi PDPDP
DiP
i
LiP
DiP
iLiiLiGi PPDP
iDiGi PPP
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 15
Mechanical Power of Each Generator ( )
Linearized equation relating mechanical power
to generator power and generator speed.
Where = Small change in mechanical power of generator i
= Small change in electric power of generator i
= small change in internal voltage angle of generator i
From,
We have
GiiiiiMi PDMP
MiP
GiP
i
GiP
iLiiLiGi PPDP
iLiiLiiiiiMi PPDDMP
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 16
Generator Block Diagram
From,
We can write
where
iLiMi
ii
i PPP
DsM
~
1
iLiiLiiiiiMi PPDDMP
Liii DDD
~
ii DsM
1
s
1+-
-
MiP
LiP
i
i
iP
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 17
AGC for Multi Generators: Block Diagram
sGMi
iR
1
+
-
sGPi
iMiP
LiP
CiP
iP
+
-
-
ii
Pi
DsMsG ~
1
TiGi
Mi
sTsTsG
11
1
Change in tie-line
power flow
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 18
Tie-line Model ( )
From power flow equation,
Approximate at normal operating condition, we
have
Then, for small change,
Where is called stiffness or synchronizing power coefficient
iP
n
k
kiikkii BVVP
1
sin
n
k
kiiki BP
1
n
k
kiik
n
k
kiiki TBP
11
ikT
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 19
Tie-Line Block Diagram
From and
We have,
n
k
kiiki TP
1
s
1
n
k
ki
ik
i
s
TP
1
s1
++
+
ikT
iP
ii
+
- +
- +
-
k
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 20
AGC for 2-Generator: Block Diagram
sGM2
2
1
R
+-
sGP222MP
2LP
2CP212 PP
+
-
-2
s
-
sGM1
1
1
R
+
-
sGP1
1
1MP1LP
1CP
121 PP
+
-
-
1
s
+
-1
12T
Load
Frequency 2
Different phase angle Transfer power 12
Frequency 1
Governor 2 sense
speed , try to
mechanical power
Governor 1 sensespeed , try to
mechanical power
Steady state: New
(lower) system
Frequency
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 21
AGC for 2-Generator:
Static Speed-Power Curve
Load increases.
Frequency drops.
Steady state is reached
when frequency of bothgenerators is the same.
1MP 2MP
MP
1
2
0
+ = Change in
total load
1MP 2MP
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 22
Steady State Frequency Calculation:
2 generators
From
Consider the frequency at steady state,
But, , ,and
Then,
iLiiiiLiiiiiMi PPDPPDMP ~~
linetieLM PPDP 1111
~
linetieLM PPDP 2222 ~
21 1
1
1
RPM
2
2
1
RPM
21
21
21
11~~
RRDD
PP LL
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 23
Note that
In single area- multi generators case, we have
not discuss how to systematically bring back the
new steady state frequency by adjusting control
power. We will discuss this in the following section.
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 24
AGC for Multi Areas
Simplified Control Model
Area Control Error (ACE) Example 11.5
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 25
Simplified Control Model
Generators are grouped into control areas.
Consider An area as one generator in single area, and,
Tie-lines between areas as transmission linesconnecting buses in single area.
We can apply the same analysis to multi-area!!
However, we have to come up with frequency-
power characteristics of each area. Actual application of this model is for power pool
operation.
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ELEN 460:Power System Control and Operation:Automatic Generation Control (AGC) 26
Power Pool Operation
Power pool is an interconnection of the powersystems of individual utilities.
Each company operates independently, BUT,
They have to maintain contractual agreement about power exchange of
different utilities, and,
same system frequency.
Basic rules Maintain scheduled tie-line capacities.
Each area absorbs its own load changes.
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 27
AGC for Multi Areas
During transient period, sudden change of load causes
each area generation to react according to its frequency-
power characteristics.
This is called primary control.
This change also effects steady state frequency and tie-
line flows between areas.
We need to
Restore system frequency,
Restore tie-line capacities to the scheduled value, and,
Make the areas absorb their own load.
This is called secondary control.
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 28
Area Control Error (ACE)
Control setting power of each area needs to be
adjusted corresponding to the change of
scheduled tie-line capacity and change of
system frequency. ACE measures this balance, and is given by,
for two area case.Where = Frequency bias setting of area i (>0) and
1121 BPACE
2212 BPACE
iB
i
Lii
RDB
1
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 29
ACE: Tie-Line Bias Control
Use ACE to adjust setting control power, , of
each area.
Goal:
To drive ACE in all area to zero. To send appropriate signal to setting control power,
Use integrator controller so that ACE goes to
zero at steady state.
CiP
CiP
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 30
AGC for 2-Area with Tie-line Bias Control:
Block Diagram
sGM2
2
1
R
+ -
sGP2
22MP
2LP
2CP212 PP
+
-
- 2s
-
sGM1
1
1
R
+-
sGP1
1
1MP1LP
1CP
121 PP
+
-
-
1
s
+
-112T
-1
+
+
+
+
s
K2
s
K1
1
2
12P
21P
1B
2B
1ACE
2ACE
Load 2
Frequency 2
Different phase angle Transfer power 12
Frequency 1
Governor 2 sense
speed , try to
mechanical power
Governor 1 sense
speed , try to
mechanical power
ACE 2 < 0
ACE 1 = 0
Setting control power 2
Frequency 2
Different phase angle
Governor 2 sense
speed , try to
mechanical power
Transfer power 12
Governor 1 sense
speed , try to
mechanical powerFrequency 1
Steady state:
Maintain Frequency
Set control power 2 > 0
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 31
AGC for 2-Area with Tie-line Bias Control :
Static Speed-Power Curve
Load in area 2 increases.
Frequency of both area
drops.
ACE makes Control
power of area 2
increases.
Steady state is reached
when frequency is back
at the operating point andgenerator in area 2 take
its own load.
1MP 2MP
MP
1
2
0
+ = Change in load 2
1MP 2MP
2
1MP
2MP
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 32
Example 11.5
Two-area system,
Find change in frequency, ACE, and appropriatecontrol action.
A B
MW100000 A
L
A
G PP MW000,1000
B
L
B
G PP
sec/MWperrad015.0A
R sec/MWperrad0015.0B
R0 BL
A
L DD
MW10 ALP
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 33
Example 11.5: Frequency Calculation
From,
And,
And,
We have,
21
AB
A
LAB
A
LA
A
L
A
M PPPPDP
BABA
B
LB
B
L
B
M PPPDP
A
A
MR
P1
B
B
MR
P1
secperrad0136.0
0015.0
1
015.0
1
10
11
BA
AL
RR
P
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 34
Example 11.5: ACE Calculation
First, find from
Then,
MW9091.00136.0015.0
11
A
A
M
RP
MW091.9 A
L
A
MABAB
A
L
A
M PPPPPP
MW091.9 ABBA PP
ABP
MW100136.0015.01091.91
A
ABA
RPACE
MW00136.00015.0
1091.9
1
B
BAB
RPACE
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ELEN 460:Power System Control and Operation:
Automatic Generation Control (AGC) 35
Example 11.5: Control Action
ACE indicates each area action to the change of
load.
ACE of area B is zero, this means that nothing
should be done in area B. ACE of area A < 0, this means that area A
should increase the setting control power by
(-10) = 10 MW to cover its own load.