facts flexible ac transmission systempeople.qatar.tamu.edu/shehab.ahmed/ecen_459/facts.pdf ·...
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Dr Ahmed Massoud University of Strathclyde 1
FACTSFlexible AC Transmission
System
Presented by: Dr Ahmed Massoud
Dr Ahmed Massoud University of Strathclyde 2
FACTS1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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POWER SYSTEM
GENERATION TRANSMISSION DISTRIBUTION
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Characteristics of Transmission Bottlenecks
• Steady-State Power Transfer Limit• Voltage Stability Limit• Transient Stability Limit• Thermal Limit• Short-Circuit Current Limit
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Conventional System Solutions toenhance Transmission capability
• Series Capacitors (X)• Switched Shunt-Capacitor and Reactor (V)• Transformer LTC’s (V)• Phase Shifting Transformers (δ)• Synchronous Condensers (V)
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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FFlexible AAlternating CCurrent TTransmission SSystems (FACTS)
FACTSAC transmission systems incorporating the power electronic-based to enhance controllability and increase power transfer capability.
FACTS ControllersA power electronic based system & other static equipment that provide control of one or more AC transmission parameters.
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Power Electronics Devices For FACTS Controllers
Line-Commutated• Thyristors• Electrically Triggered (ETT)• Light Triggered (LTT)Self-Commutated• Gate-Turn Off Thyristors (GTO)• Insulated Gate Bipolar Transistors (IGBTs)• Integrated Gate Commutated Thyristors (IGCTs)
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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FA C TS con tro lle rs
line com m utated
Seriesthy ris to r contro lled
se ries capac ito r(TC SC )
Shuntthy ris to r contro lled reac to r o r sw itched capac ito r (TCR or TS C)
forced com m utated
Seriesstatic synchronous
series compensator(SSSC)
Shunts ta tic synchronous
compensa to r (STATC O M )
Shunt-Series unified pow er flow
contro lle r (UPFC)
Series-series inte rline power flow
contro lle r (IPFC)
Back-to -backconventiona l HVD C
Series-series inte rline pow er flow
contro lle r (IPFC )
Ba tte ry ene rgy s to rage (BESS)
Superconduc ting M agne tic Energy S to rage (SM ES)
Back-to -back light HVDC
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X
. sins rV VPX
δ=
___
sV___
rV
δ
I
I.X
sV
rV
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Controllable parameters Control of the line impedancecurrent and active power control Control of anglecurrent and active power controlSeries voltage injectionCurrent, active, and reactive power controlParallel voltage injectionCurrent, active, and reactive power control
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Series control
Vseries
XXseriesV1 V2
V1
V2δ
I
P=V1.V2.sin(δ )/(X-Xseries)
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Parallel control
P=V1.V2.sin(δ )/X
Q
XV1 V2
V1
V2δ
II
V1
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Series and parallel control
Q
XV1 V2
Vseries
Xseries
??
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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Static VAR compensator
• TCR = Thyristor Controlled Reactor• TSR = Thyristor Switched Reactor• TSC = Thyristor Switched Capacitor• MSC = Mechanically-Switched Capacitor• MSR = Mechanically-Switched Reactor• FC = Fixed Capacitor• Harmonic Filters
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Thyristor Controlled Reactor (TCR)Parallel-connected static var generator or
absorber● Output is adjusted to exchange capacitive or
inductive current● Maintain or control specific parameters of the
electrical power system(typically bus voltage).
● Thyristor-based Controllers● Lower cost alternative to STATCOM
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0 0.005 0.01 0.015 0.02-1
-0.667
-0.333
0
0.333
0.667
1
Time (s)
0 0.005 0.01 0.015 0.02-8
-6
-4
-2
0
2
4
6
8
Time (s)
Voltage Current Thyristor ControlledReactor
Firing angle of 135
Firing angle of 90
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Thyristor Switched Capacitor (TSC)
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Static Synchronous Compensator (STATCOM)
● Parallel-connected static var compensator● Capacitive or inductive output current
controlled independently of the acsystem voltage
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Q
P (if no energy source is provided)
Inverter (IGBT, GTO, or GCT)
Vdc
L
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Parallel Active Power Filters (Parallel APF)
• Reactive power• Compensation• Source current’s higher• Harmonics compensation• DC element voltage control
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3-phase supply
non-linear load
i s
i L
Le
v Shunt active filteri f
Shunt active power filter single line diagram
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C
Sa Sb Sc
S'a S'b S'c
v an
v bn
v cn
v dc (t)
La
i dc (t)
i a
+_
e a
e b
e c
i b
i c
Lb
Lc
Two level voltage source inverter
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Voltage source inverters
1. Two level Voltage source inverter2. Multilevel voltage source inverter3. Series connection
Current source inverter ?
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Multilevel inverter
1. Neutral point clamped2. Cascaded 3. Flying capacitor
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Neutral point clamped
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Flying capacitor
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Cascaded
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2E
E
E
i loadS1
S4
S5
S8
2E
E
E
i loadD1
D4
D5
D8
2E volt
iload >0 iload <0
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E
E
E
i load
D 3 S4
S5
S8
E
E
i load
S3 D 4
D 5
D 8
E
iload >0 iload <0
E volt
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0
E
E
i load
D 3 S4
D 7 S8
0
E
E
i load
S3 D 4
S7 D 8
iload >0 iload <0
0 volt
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-E
E
E
i load
D 3 S4
D 7
D 6
-E
E
E
i load
S3 D 4
S6
S7
iload >0 iload <0
-E volt
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-2E
E
E
i loadD 2
D 3
D 6
D 7
-2E
E
E
i loadS2
S3
S6
S7
iload >0 iload <0
-2E volt
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Output of 5-level inverter (PWM)
0 0. 005 0.01 0.015 0.02-3
-2
-1
0
1
2
3M
agni
tude
(P
er u
nit)
T ime (s )
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Series connection of IGBT
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Output of two-level inverter (PWM)
0 0. 005 0.01 0.015 0. 02-3
-2
-1
0
1
2
3
T im e (s )
Mag
nitu
de (
Per
unit
)
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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Series Capacitors Applied For:Increasing Power TransferIncreasing Stability LimitsImproving Voltage ProfileImproving Load Division
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Series Active Power filter (Series APF)
• Voltage harmonics compensation• Stability improvement• Current harmonics blocking
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Static Synchronous Series Compensator (SSSC)
● Output voltages in quadrature with, and controllable independently of, the line current
● Control the transmitted electric power.● May include energy storage to enhance the
dynamic behavior of the power system by additional temporary real power compensation, to increase or decrease momentarily, the overall real (resistive) voltage drop across the line.
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● Smooth control of series capacitive reactance
Thyristor Controlled Series Capacitor (TCSC)
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers7. HVDC8. Others
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Unified Power Flow Controller (UPFC)
● A combination of STATCOM and SSSC coupled via a common dc link
● Bi-directional flow of real power between the SSSC and the STATCOM
Unified Power Flow Controller = Static Synchronous Series Compensator + STATCOM
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In ve r te r (I G B T , G T O , o r G C T )
C
L
S e r ie s c o n v e r te r
S h u n tc o n v e r te r
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Unified Power Quality Conditioner (UPQC)
• Source current harmonics compensation• System stability improvement• Reactive power compensation• DC element voltage control• Voltage harmonics compensation
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Combination of active power filter and passive filter
LoadSupply
Active filter
Passivefilter
Parallel active power filter and passive filter
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Parallel active power filter in series with passive filter
LoadSupply
Active filter
Passivefilter
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LoadSupply
Passivefilter
Active filter
Series active power filter and parallel passive filter
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LoadSupply
Activefilter
Active filter
Series and parallel active power filter (unified power quality conditioner UPQC)
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Series VS. Parallel
● Series is more powerful in controlling the current/power flow and damp oscillations
● Parallel is more effective in voltage control and damping of voltage oscillations
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others
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FACTS and HVDC
V1 V2FACTS or
HVDC
Grid 1 Grid 2
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High voltage DC transmission (HVDC)
It is economically attractive:• over a long distance from a remote
generating to the load centre (>300 miles)
• underwater transmission• when connecting two AC systems at two
different frequencies
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Advantages of HVDC• No limits in transmitted distance. • Fast control of power flow, which implies stability
improvements. • Direction of power flow can be changed very quickly. • HVDC can carry more power for a given size of conductor• improved transient stability • dynamic damping of the electric system oscillations • Require less space compared to ac for same voltage rating
and size• Ground can be used as a return conductor• No charging current• HVDC transmission limits short circuit currents
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Distance
Cost
DC Cost
AC Cost
600-800Km
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The HVDC technologyThe fundamental process that occurs in an HVDC system
is the conversion of electrical current from AC to DC (rectifier) at the transmitting end, and from DC to AC (inverter) at the receiving end.
1. Natural Commutated Converters. The component that enables this conversion process is the thyristor (high power and low switching frequency).
2. Forced Commutated Converters. It uses GTO or IGBT. They are known as VSC (Voltage Source Converters).
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Y
Δ
Y
Y
Y
Δ
Y
Y
AC filter and power factor
correction capacitors
AC system
A
DC filter
DC filter
L d
L d
Positive pole 12 pulse
Terminal A
Negative pole 12 pulse
HVDC transmission
line
Terminal B AC system
B
HVDC transmission system
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Components of HVDC 1. Converter: at one side rectifier and the other inverter
each converter consists of a positive pole and a negative pole each pole consists of 6 pulse converters connected through star-delta and star-star transformer to yield 12 pulse converter
2. On the AC side:* AC filters to reduce the current harmonics generated from the converters* Power factor correction capacitors to supply the lagging reactive power
3. On the DC side: smoothing reactor and DC filters to filter the ripple in the DC currents
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12 pulse line frequency converterObjectives:1. Reduce current harmonics on AC side 2. Reduce voltage ripple on DC side3. High power
12 pulse converter consists of two six-pulse converters connected through star-star and delta-star transformer
The 2 converters are connected in series from the DC side and parallel from the AC side
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L d
2N:1
2 N:13
i a i a1
i a2
I d
i as1
i as2
as1
bs1cs1
as2
bs2
cs2
n1
n2
v d1
v d2
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Types of HVDC links1. Monopolar: Having one conductor and the ground is
the return path
return earth
DC pole
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+ DC pole
return earth
- DC pole
2. Bipolar: There are two conductors (poles). One operates with positive polarity and the second with negative. During fault of one them, the bipolar acts as a monopolar
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HVDC Light
1. HVDC Light unit sizes range from a few tens of MW to presently 350 MW and for DC voltages up to ±150 kV and units can be connected in parallel.
2. HVDC Light consists of two elements: converter stations and a pair of cables. The converter stations are Voltage Source Converters (VSCs) employing Self-commutated switch
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FACTS
1. POWER SYSTEMS2. FACTS definition3. FACTS controllers4. Parallel controllers5. Series controller6. Series-parallel controllers 7. HVDC8. Others Battery Energy Storage System Super conducting material