Active Power Filters
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Transcript of Active Power Filters
1
A Reviewof
ACTIVE POWER FILTERS
Prepared byPARK KI-WON
R&D Center , POSCON
2001. 02. 09
2
1. Issues on Harmonics
Nature of Harmonics• Generalized power theory• Measurement / Metering
Impacts of Harmonics• Parallel / Series Resonance, RMS / Peak Value Increase
Source of Harmonics• Voltage source vs.Current source• Static vs. Dynamic
Standards on Harmonics: Harmonic Limits• Utility companies / Customers / Manufacturers• IEC / IEEE
Harmonics Reduction/Elimination
3
2. Source of Harmonics
Non-linear magnetization of a transformer• Very small compared to rated current
Power electronics based equipment• UPS, PC, Welder, Printer• Rectifier, Variable Speed Drive• Due to discontinuous current flows
[ ]Wbφ
[ ]Ai [sec]t
( )tφ ( )ti
4
( )tiline
CLoadLoadLoadLoad
ACACACACSupplySupplySupplySupply
Voltage Source Type Harmonic• Diode rectifiers with capacitive filtering
5
Current Source Type Harmonic• Thyristor converters with inductive filtering
( )tiline
L
LoadLoadLoadLoadACACACACSupplySupplySupplySupply
6
3. Standards/Guides on Harmonic Limits
IEC 1000-3-2( International Electrotechnical Commission )• Harmonic current emission limits for individual equipments• Small equipments < 16A• European standard (CELENEC)
IEC 1000-3-4• Harmonic current limits of overall installation• Medium to large installations >16A• Related to line stiffness (SCC)
IEEE 519-1992• Limits at PCC (Interfacing)• Harmonic voltage limits for utility company• Harmonic current limit for customers(<69kV)• Related to line stiffness
7
4. How Harmonic Reduction/Elimination?
Line-Friendly Load• Multi-pulsed system : Series and/or parallel• Active current shaping( PFC converter )
Passive Filters• Simple, low cost, robust• Sensitive to environments: line impedance, load change, ageing of component• Subject to parallel/series resonance• Easily overloadable : switch off or be damaged, plant modification• Over Compensation at which have already a good power factor
Active Filters
8
Series vs. Shunt
Shunt Tuned Filter• High voltage: 50 < Q < 150• Low voltage: 10 < Q < 50
LC1
C
L
R
ω
CL
RQ 1=
Cω1
Lω
R
FZ
)(ωFZ
5. Passive Filters
9
LC1
C
L
R
FZ
ω
Cω1
Lω
R
)(ωFZ
bR
bR
CRb
1
Damped High-Pass Filter (2nd order)
10
Non-linear load
Power system
I5 I7 I11 Ih IS ≅ I1
IL
5th tuned filter
7th tuned filter
11th tuned filter
High-pass filter
Typical Passive Filter System
11
6. Parallel Resonance
• Due to load current harmonic • Voltage distortion will be very high• Overvoltage
ACACACACSupplySupplySupplySupply
L
C
parallelZ
hihi
)1(11
12
2 =∞⇒−
=+
= LCwhenLC
Lj
CjLj
CjLj
Z parallel ωωω
ωω
ωω
12
Parallel Resonance with Passive Filter
FZ
SZ
LhI
ShI LhI
FhI
FSSF ZZZ ||=
LC1
R
ω
Cω1
Lω
)||( LLSω
SLω
1 (0dB)
CLS
1 CLLS )||(
1
Lh
ShII
SFZ
LLL
S +
CLS21
ω
Parallel resonance Tuned frequency
CLLS )(1+
CLLSp
)(1+
≈ω
CLL
RRQ S
Sp
++
≈ 1
13
Possible Cause of Parallel Resonance• Detuning Filter : shift of resonance frequency• Capacitance change due to fuse blow• C and L may be damaged• Temperature• Line structure change
Typical Design Practice• Tuned to slightly lower harmonic frequency (3~10%)
Effect of Ls (SCC)• High Ls : good for avoiding parallel resonance• Higher Ls : Higher Q for parallel resonance
14
7. Series Resonance
hv
DistortedDistortedDistortedDistortedSupplySupplySupplySupply
L
C
seriesZ
hi
hv
)1(011C
LwhenC
LjCj
LjZseries ωω
ωω
ωω =⇒
−=+=
• Due to line voltage harmonics• Excessive harmonic current flow• Overload, Breakdown
15
Series Resonance Due to Neighborhood Harmonic Source
1TRZPCCPCCPCCPCC
hi
............
Plant #1Plant #1Plant #1Plant #1
2TRZ
Plant #2Plant #2Plant #2Plant #2
ACACACACSupplySupplySupplySupply
FilterFilterFilterFilter
16
Equivalent Circuits Transforms
hI
2TRZ
LIFZ1TRZ
ShV LIFZ
1TRZ 2TRZ
SZ
1TRhSh ZIV =
PCC
• Series Resonance
will be occurred
17
8. Troubles due to Harmonic Pollutions
• Heating of the electrical equipment• Trip of circuit breaker• Fuse blown• Capacitor damage• kWh fault• Loss of motor winding and iron• Perturbing torques on the motor shaft• Damage of Sensitive electronic equipment• Malfunction of PLL circuit• Communication interference
• Parallel and Series Resonance will occured• Increase of RMS and Peak Value• Excessive Neutral Currents
18
9. Motivations for taking action against Harmonics
Harmonics lead to premature ageing of the electrical Installation
• Excessive amount of harmonics must eliminatefor economic reasons
The utility company impose penalties on users
• Harmonic pollution may disturb equipment in other plants• THD limitation of voltage / current present at PCC• IEC 1000-3-6 : “Assessment of emission limits for disturbing loads
in MV and HV power systems”
19
10. Function of APFs
Main function• Compensate current and voltage harmonic.
Additional functions• Current-related compensation
• Reactive power, current unbalance, neutral current• Using shunt-APF for the most part
• Voltage-related compensation• Voltage unbalance, flicker, spikes, regulation• Using series-APF for the most part
20
Converter-based classification• VSI (Voltage Source Inverter) bridge structure• CSI (Current Source Inverter) bridge structureTopology-based classification• Shunt APF• Series APF• UPQC : Shunt APF + Series APF• Hybrid APF : Shunt or Series Active Filter + Passive Filter
Supply-system-based classification• Two-wire APF• Three-wire APF• Four-wire APF
11. Classification of Active Filters
21
12. Converter based classification
CSI
• Switching frequency is restricted
• Higher losses
• Cannot be used in multilevel
VSI
• Self-supporting dc voltage
• Lighter, cheaper
• Expandable to multilevel
22
Shunt APF stand-alone
• Eliminate current harmonics
• Reactive power compensation
• Balancing unbalanced current
NonlinearLoad
Shunt Active FilteriF
NonlinearLoad
Seies Active Filter
vF
13. Topology based classification
Series APF stand-alone
• Eliminate voltage harmonics
• Regulate and balance the terminal voltage
• Damp out harmonic propagation
23
Nonlinear Load
optional
Series Shunt
UPQC : Unified Power Quality Conditioner
• Eliminate voltage and current harmonics• Damp out harmonic propagation• Load voltage regulation and current balancing• Another name is “Universal APF”• Fundamental power flow control: Low power version of UPFC in FACTS• Large cost and control complexity
24
Hybrid APF( Combinations of Passive-Active )
Parallel combination of shunt-APF and shunt passive filter• Current source vs. Harmonic sinkSeries combination of series-APF and series passive filter• Voltage source vs. Harmonic dampingHybrid of series-APF and shunt passive filter• Harmonic isolation vs. Harmonic compensation• Reduced size and cost : Quite popularHybrid of shunt-APF and series passive filter• Harmonic isolation vs. Harmonic blocking Series combination of shunt-APF and shunt passive filter• Resonance damping vs. Harmonic compensationParallel combination of series-APF and series passive filter• Enhancing passive filter vs. Harmonic blocking
25
NonlinearLoad
Shunt Active Filter
Nonlinear
Load
Series Active Filter
• Harmonic cancellation• Q control• Optimal sharing is needed• Commercialized
• Harmonic damping• Existing passive filter• Low power• More circuit for Q control• Overcurrent protection
is difficult
Parallel combination ofshunt-APF and shunt passive filter
Hybrid ofseries-APF and shunt passive filter
26
NonlinearLoad
Series Active Filter
• Harmonic cancellation and damping• Series-APF enhanced existing passive filter• Easy protection is possible• Current Transformer is minimized• No Q control• Under developed
Series combination ofseries-APF and shunt passive filter
27
14. Supply-system based classification
Two-wire APF
• Single-phase nonlinear loads, such as domestic appliances
• Smaller rating
Three-wire APF
• Three-phase nonlinear load without neutral, such as ASD’s
Four-wire APF
• Single-phase nonlinear loads fed from four-wire supply system,
such as computers, commercial lighting
• Eliminate excessive neutral current and unbalance
28
Capacitor midpoint four-wire shunt APF• Used in smaller ratings,
because entire neutral current flows through dc bus capacitor
Sae
Sbe
Sce
Sai
Sbi
Sci
Lai
Lbi
Lci
Cav
Cbv
Ccv
cL
n
CaiCbiCciCni
Sni
dcC
Non-Linear Four-wireUnbalanced Loads
Lni
n
dcC
29
Four-pole four-wire shunt APF• Fourth pole is used to stabilized the neutral of APF
Sae
Sbe
Sce
Sai
Sbi
Sci
Lai
Lbi
Lci
CavCbv
Ccv
cL
n
CaiCbiCciCni
Sni
dcC
Non-Linear Four-wireUnbalanced Loads
Lni
n
30
Three-bridge four-wire shunt APF• Quite common type• Proper voltage matching for IGBT, Enhances the reliability of APF
Sae
Sbe
Sce
Sai
Sbi
Sci
Lai
Lbi
Lci
Cbv Ccv
n
Cai Cbi Cci
Sni
dcC
Non-Linear Four-wireUnbalanced Loads
Lni
Cav
31
First stage : Signal conditioning• Sensing system information by PT, CT, Isolation amplifiers• Monitor, measure, record
: THD, power factor, active/reactive power, crest factor…Second Stage : Derivation of compensating signal• Current level and/or voltage level• Frequency domain
: Based on Fourier transformation: Cumbersome computation, large response time
• Time domain: Based on instantaneous derivation: pq theory, synchronous dq reference frame method, synchronous
detection method, flux-based controller, notch filter method…Third stage : Generation of gating signal• Hysteresis, PWM, SVPWM, sliding mode, fuzzy-logic…
15. APF Control Strategies
32
16. Component considerations of APF
Series inductor : buffer between supply and PWM voltagePassive ripple filter : suppress switching harmonic and improve source THDDC bus capacitor : reduces dc ripples
Cai
Cbi
Cci
Cav
Cbv
Ccv
cL
dcCdcv
p
n
dci
dc bus capacitor
passive ripple filter
series inductor
IGBT
33
17. Basic Concept of Active Filter Control
Active Filter as a “Harmonic Canceller”
Harmonic current detection
And
Current control method
Harmonic voltage detection
And
Voltage control method
SL
Shunt-APF
fS ii = hfL iii +=
hC ii =
detectionih
Sv Li
SL
Series-APF
hC vv =
hf
S
vvv
+=
detectionvh
Sv LifL vv =
34
Active Filter as a “Harmonic Damper”
SL
Shunt-APF
h
hC Z
vi =
detectionvh
Sv Li
SL
Series-APF
hhF iZv =
detectionih
Sv Li
Harmonic voltage detection
And
Current control method
Harmonic current detection
And
Voltage control method
35
18. Control Based on Synchronous d-q Transformation
• Definition of Synchronous d-q transformation
32,
)sin()sin(sin)cos()cos(cos
32 πγ
γθγθθγθγθθ
=
+−−−−
+−=
where
fff
ff
c
b
a
q
d
−
=
−=
s
q
sd
ee
eee
q
ed
eq
ed
ee
ees
q
sd
ff
ff
ff
ff
θθθθ
θθθθ
cossinsincos
,cossinsincos
∑∑
=
=
+=+=
+=+=
mkqkm
eqh
eq
eq
mkdkm
edh
ed
ed
iIiii
iIiii
311
311
sin
cos
φ
φ
• Transformed current with harmonics
( ) ( )
( ) ( )[ ]
( ) ( )[ ]kek
mkemb
kek
mkemb
kek
mkema
kIIi
kIIi
kIIi
φγθφγθ
φγθφγθ
φθφθ
−++−+=
−−+−−=
−+−=
∑
∑
∑
∞
=
∞
=
∞
=
coscos
coscos
coscos
21
21
21
36
Axes relation between abc and dq
• Stationary frame • Synchronously rotating frame
aa ff =
32πj
bb eff ⋅=
32πj
cc eff−
⋅=
sdf
sqf
γ
γ−
aa ff =
32πj
bb eff ⋅=
32πj
cc eff−
⋅=
sdf
sqf
eθγ +
eθγ +−
edfe
qf
eθ
37
D-Q variable in time domain
Sae Sbe Sce
mE
π π2
π
π−
teω
t
sSqes
Sde
mE
π π2teω
eSde
eSqe
mE
π π2teω
• Stationary
• Synchronously
38
Harmonic locus in Space Vector
5th in stationary frame 7th in stationary frame
tjm
tjm
sssdq
ee eFeFfff ωω 551 5
151 −+=+= tj
mtj
msss
dqee eFeFfff ωω 7
71 71
71 +=+=
sdqf
eω
sf1
sf5eω5−
sdf
sqf
sdqf
eωsf1
sf7eω7
sdf
sqf
39
5th and 7th in stationary frame 5th and 7th synchronous rotating variable in stationary frame
tjm
tjm
tjm
ssssdq
eee eFeFeFffff ωωω 75751 7
151
71
51 ++=++= −
tjm
tjmm
eeeedq
ee eFeFFffff ωω 66751 7
151
71
51 ++=++= −
sdf
edqf
sqf
sdqf
eωsf1
sdf
sqf
40
Overall block diagram of shunt-APF controller
Lai
Lbi
eLdi
eLqi
LPFeLdi
===
)1(0)0(
KKii
eLde
Sd
+ −
LPF
+ −
1-K
eLqi e
LqeSq ii =
*eCdi
*eCqi+ −
IPcontroller
*dcv
dcv
+
−
synchronousPI-controller
eθeθ
*eCdv
*eCqv
seTjke ω
*'eCdv
*'eCqv
e→φ3 se →
*sCdv
*sCqv
SVPWM
*aT
*bT
*cT
e→φ3
Cai
Cbi
eCdi
eCqi
HarmonicPhase DelayCorrection
41
Harmonic Phase Delay Correction Method
)(* ki eC
LPF
)(*1 ki e
C
)(*5 ki e
C
)(*7 ki e
C
5CI
7CI
seTje ω6−
LPF
5th Harmonic detection
7th Harmonic detection
+
−
seTje ω6
)(*11 ki e
C
)(*13 ki e
C
+
+
+
+
LPF1CI
Fundamental detection
+
+
+
)1(*1 +ki e
C
)1(*5 +ki e
C
)1(*7 +ki e
C
+
+
+
+
+
+
)1(*11 +ki e
C
)1(*13 +ki e
C
+
+)1(* +ki e
C
eje θ6
eje θ6 eje θ6−
eje θ6−
Harmonic phase delay correction in synchronous rotating frame
42
19. Control Based on p-q Theory
=
−
−−=
c
b
a
c
b
a
eee
Ceee
ee
αββ
α
23
230
21
211
32
=
−
−−=
c
b
a
c
b
a
iii
Ciii
ii
αββ
α
23
230
21
211
32
aa ie ,
bb ie ,
cc ie ,
32π
32π
32π
a-Axis
b-Axis
c-Axis
0
αα ie ,
ββ ie ,
α-Axis
β-Axis
0
αααα- ββββ Transfomations
43
ccbbaa ieieiep ++=
ββαααβαβββαα ieieiepieiep ⋅+⋅=⋅=+= ,
αββααβαβαββα ieieieqieieq ×+×=×=−= ,
• Conventional instantaneous power
βα ie ×
αβ ie ×
αeαi
βiβe
REAL PLANE
IMAGINARY AXIS
α-Axis
β-Axis • Instantaneous real power
• Instantaneous imaginary power
−
=
−
=
−
qp
eeee
ii
ii
eeee
qp
1
,αβ
βα
β
α
β
α
αβ
βα
• Instantaneous power vs. current
44
p and q in Sinusoidal Case
tVva ωcos2=
)cos(2 γω += tVvb
)cos(2 γω −= tVvc
)cos(2 φω −= tIia
)cos(2 γφω +−= tIib
)cos(2 γφω −−= tIic
tVv ωα cos3=
tVv ωβ sin3=
)cos(3 φωα −= tIi
)sin(3 φωβ −= tIi
φββαα cos3VIivivp =+=
φαββα sin3VIivivq =−=
45
p and q in Non-Sinusoidal Case
46
Overall block diagram of series-APF controller
Fav
Fbv
Fcv
HPF
HPF
αFv
βFv
Sai
Sbi
Sci
αSi
βSi
p
q
hp
hq
a
b
c
d
q
0=θ
a
b
c
d
q
0=θ
−
=
β
α
αβ
βα
S
S
FF
FF
ii
vvvv
qp
−
=
−
h
h
FF
FF
hS
hS
qp
vvvv
ii 1
αβ
βα
β
α
hSi α
hSi β
a
b
c
d
q
0=θ
K
K
K
Sahi
Sbhi
Schi
*Cav
*Cbv
*Ccv
47
20. Selection of APF for specific considerations
9. Voltage Sag & Dips
8. Voltage Flicker
7. Voltage Balancing
6. Voltage Regulation
5. Voltage Harmonics
4. Neutral Current
3. Load Balancing
2. Reactive Power
1. Current Harmonics
UPQCHybrid-APFSeries-APFShunt-APF
Active Power Filters TopologyCompensation for specific application
Higher number of ‘ ’ is more preferred