Power Quality Enhancing Systems Industrial Electrical ...
Transcript of Power Quality Enhancing Systems Industrial Electrical ...
Industrial Electrical Engineering and AutomationLund University, Sweden
Power Quality Enhancing Systems
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1. ObjectivesDiscuss the problems related to harmonics in the power system and present some methods to reduce the problems.
• Single-phase diode rectifiers and power factor correctors
• Three-phase diode rectifiers
• Controlled three-phase diode rectifiers: Minnesota and Vienna
• The voltage source converter
• Series and shunt active filters, the unified power flow controller
• Detection and identification of harmonic currents
• Effect of blanking time and forward voltage drop
• Multiple rotating coordinate systems
• Simulation and measurement results
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Acronyms
• APF – Active Power Filter• UPFC – Unified Power Flow Controller• SVC – Static Var Converter• HVDC – High Voltage Direct Current• ...
All made to improve ”Power Quality”
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Non-ideal loads
• are loads that:– are non-resistive -> consume reactive power– vary with time or phase -> consume harmonic
current components.– are different in different phases -> consume
negative sequence currents
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nWays to improve the loads
• Self improvement– Solutions that draw as “ideal” current as
possible from the grid• Compensation
– A parallel unit is used to counteract the non ideal currents drawn by the main load
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2. Single-phase diode rectifiers (I)A single-phase diode rectifier draws a line current with a large harmonic content since the diodes must be forward biased to conduct.
Lline
iline
eLN C
dcv
dc
D1
D2
D3
D4 0 0.005 0.01 0.015 0.02
−100
−75
−50
−25
0
25
50
75
100
t [s]
i line [A
]
0 300 600 900 1200 1500 1800 21000
5
10
15
20
f [Hz]
i line
,pk(f
) [A
]
0 0.005 0.01 0.015 0.02−400
−300
−200
−100
0
100
200
300
400
t [s]
v dc [V
]
eLN
−eLN
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2. Single-phase diode rectifiers (II)The current harmonics create voltage harmonics at the point of common coupling (PCC), i.e. at the point where other loads are connected. Note that all single phase diode rectifiersdraws current in the vicinity of the peak voltage.
+
-
V4
100
D11
D12 D14
D13
R16
1
1
1
1
CDC1m
0
Time
0s 2ms 4ms 6ms 8ms 10ms 12ms 14ms 16ms 18ms 20ms
V(R16:1)- V(R16:2) V(V4:+)- V(V4:-)
-200V
0V
200V
-325V
325V
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2. Power Factor Corrector (PFC)
22
0.01
0.01
+
-
V4
Driver
0.1
30
D12 D14
D13
L1
1000uH
D1
Z2
IXGH40N60
+
-
360V V3
10000+
- G=1E6U4R10
D11
+-
G=1U5
+-
G=0.1/325U6
0
0
Time
0s 2ms 4ms 6ms 8ms 10ms 12ms 14ms 16ms 18ms 20ms
I(L1)
0A
10A
20A
30A
SEL>>
V(V4:+)- V(V4:-)
0V
-325V
325V
Implemented with tolerance-band (or hysteresis) current controller.
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n3. Three-Phase diode rectifiers
Note that for three-phase diode rectifiers, only two phases carry current simultaneously. This means that each diode has a maximum conduction interval equal to 120 for each half period. Therefore a three-phase PFC is not possible to implement. However there are two types of controllable diode rectifiers derived from three single-phase diode rectifiers (which is also possible to implement):
• The Minnesota rectifier invented by Ned Mohan
• The Vienna rectifier invented by Johann Kolar
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3. The Minnesota Rectifier
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3. The Vienna Rectifier
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Load model
2
00
tj
ttj
t
eE
je
dteEdte ie
t
2t
d
q
e Loadi
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nReactive power
• A phase lag between the voltage and thecurrent:
• In flux coordinates:ie
t
2t
d
q
2ˆ2
3 jei
tjei2
3
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Assymetric load
• The phase currents are not equal inamplitude or phase lag ...
0 1 2 3 4 5 6 7-10
-5
0
5
10
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An assymetric load current vectorin the ( )-frame
2ˆˆ
3
2ˆ2
3,ˆ,ˆ
ˆ2
3
2
ˆ3
3
2
2
ˆ3
3
2,ˆ
2ˆ
2ˆ
2ˆ
3
2
2ˆ
2ˆ1
2ˆ
3
2
3
2
0
3
2
3
4
3
2
3
4
3
43
4
3
4
3
23
2
3
2
cosˆ
ctjctj
ctj
xcx
tjtjtj
tjtjxx
ctjctj
c
btjbtj
batjatj
a
jctjctj
c
jbtjbtj
b
atai
atjatj
a
eeiieiiiii
eieeei
ei
ii
eei
eei
eei
eee
ieee
iee
ii
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An assymetric load current vectorin the (d,q)-frame
!2
2322
!
22
2
23
2
2
2
2
ˆˆ6
1ˆ23
ˆ23
2ˆˆ
32ˆ
23,ˆˆ,ˆˆ
ˆ23,ˆˆ
withbackwardsRotating
tj
movingNot
j
c
j
j
tjtj
tj
c
tjtj
xcx
tjtj
xx
tjdq
cc
cc
eeiiei
ei
eeeiieeiiiii
eeiii
eii
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• Symmetricload
• Assymetric
M-file ”Load current vectors” - demo
-10 0 10-15
-10
-5
0
5
10
15Alfa - Beta
-10 0 10-15
-10
-5
0
5
10
15d - q
-10 0 10-15
-10
-5
0
5
10
15Alfa - Beta
-10 0 10-15
-10
-5
0
5
10
15d - q
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Harmonics
• Non-linear load impedance
0 1 2 3 4 5 6 7-20
-10
0
10
20
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5’th and 7’th harmonic example with Simulink
tjtjj
dq
tjtjtj
eieieii
eieieii
67
65
21
77
551
ˆ2
3ˆ2
3ˆ2
3
ˆ2
3ˆ2
3ˆ2
3
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AFActive currentReactive currentAssymetric currentHarmonic current
- Reactive current- Assymetric current- Harmonic current
Active current
Active filtering
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nVoltage Source Converters
R Lia
+Cdc
+- ea u1au1bu1c
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Types of Active Filters
Grid LoadiLine iLoad
iAF
Cdc
VSC
Lf
Cdc
Grid Load
VSC
iLine iLoadvAF
Shunt (top) and series (bottom) active filters.
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Active Filter Combinations
Load
ShuntPassive FilterShunt AF
Load
ShuntPassive FilterSeries AF
Load
Shunt AFSeries AF
vAF
iAF
iLine iLoad
Shunt and series hybrid active filters (top) andUnified Power Flow Controller, UPFC (bottom).
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Shunt Active Filter
A d d itio n a llo ad
L o ad tob e filte red
1d ci 2d ci
1i
ge
gL
1L
lo a di
1u
cpe
Cd cU
gi
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nAC side Current Control (I)
• Vector Control with Field Orientation
)(ˆ)(ˆ
)(
2
)(ˆ
)(2
)(1
01
*11
*1
11*1 kenini
T
RL
Tkiki
R
T
Lku cp
kn
ns
s
s
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AC side Current Control (II)
• Note the cross-coupling in the line model
• This cross-coupling should be incorporated in the current controller
cpqddqq
cpdqddddqcp
dqdqdqdq
eiLiRidtdLu
eiLiRidtdLu
eiRiLjidtdLu
11111111
11111111
11111111
)(ˆ)(ˆ)(2
)(ˆ)(
2
)(ˆ)(2
)( 1*
11
01
*11
*1
11*1 kekikiLjnini
TRLTkikiR
TLku cp
kn
ns
s
s
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DC link Voltage Control System (I)
sC1
sTs11
dcidcp sT
K.
.1
1*dcu dcu*
Ci
2dci
*1dci 1dci Ci
+
+ +
-
- -
Additionalload
1dci 2dci
1i1L 1uC
dcU
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• Transfer function from reference to actual DC link voltage
• Desired denominator polynomial
DC link Voltage Control System (II)
sC1
sTs11
dcidcp sT
K.
.1
1*dcu dcu*
Ci
2dci
*1dci 1dci Ci
+
+ +
-
- -
CTTKsCTKsTssTs
sUsUsG
sUsCsTsT
KsUsU
sdcidcpsdcps
s
dc
dcUdc
dcsdci
dcpdcdc
,,,23
23
*
,,
*
11
11
111
22 2 nnnn ssssA
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• Use Symmetric Optimum
• Note that for a = 2 the poles are placed as for a Butterworth filter, i.e. maximum flat pass-band. However, the bandwidth is by far to high for practical operation.
Controller Parameters ...
sdcidci
dcp
snn
TaTTCaK
aTaa
2.
.. ,
system)stablefor1Note(,2
1
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Convert DC to AC current references
*2
.
*1
.
*11
.1
1.11.11
112
121)(
Cdcdcqcp
dcdc
qcp
dcqq
dc
qcpdc
qqcpdcdcqqcpqq
dd
qd
iieui
euii
ue
i
ieiuieidtdiLi
dtdiLRiRitp
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DC link voltage controller
Additionalload
1dci 2dci
1i1L 1uC
dcU
*
*
..2
*1
11
Cdci
dcdcdci
dcpdccp
dcq uu
sTKi
eu
i
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Active filter control
C u rren t C o n tro l
Id en tif ic a tio n
G rid L o ad
A F
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nExample of DC voltage control
>> L=0.01;>> R=1;>> Ts=0.0005;>> Tidc=9*Ts;>> Kpdc=3*Cdc/Tidc;>> Cdc=1e-4;
0 0.02 0.04 0.06 0.08 0.1600
700
800
900Udc
0 0.02 0.04 0.06 0.08 0.1-20
0
20iq* & iq
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Example with active filtering
lo a di
lo a dL
lo a dR 0 0.01 0.02 0.03 0.04 0.05-500
0
500ua
0 0.01 0.02 0.03 0.04 0.05-20
0
20ia
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Filter Current References (I)
fdcdc
dcidcpdc
cp
dc
f
floadqerActiveFiltq
loadderActiveFiltd
Tsuu
sTKi
eu
TsTs
ii
ii
1111
1*
..2,
*,
,*
,
• Note that the q-direction current reference based on the load current is high-pass filtered since the active filter should not provide active power to the load
• Note that the DC link current reference is low- pass filtered since it is important that it does not contain any 100 Hz (twice fundamental) component which would result in a negative sequence component consumed by the active filter
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Filter Current References (II)
• To avoid that the DC link current reference contains a negative sequence component Tf 10 ms is a proper choice.
• To assure that the negative sequence current consumed by the load is provided by the active filter Tf 10 ms is a proper choice.
• Use Tf = 10 ms
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nFilter Current References (III)
• Since Tf = 10 ms >> Ts 100 s (typically) the converter dynamics do not have to be included in the selection of the DC link voltage controller parameters, i.e. Gi(s)1.
• However a new low-pass filter shows up in the transfer function, e.g. the one with time constant Tf .
• This means that the transfer function looks exactly the same but Ts is replaced by Tf .
• In this case a = 2 is a proper choice for the DC link voltage controller parameters.
• Note that a = 3 gives real poles since the closed loop damping of all poles is equal to 1.
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Filter Current References (IV)
• The rather long time constant of the low-pass filter (Tf)results in the need of a comparably large DC link capacitor (C) for converters used for active filters.
• In this case the DC side load current (idc2 ) is also filtered with Tf which increases the need of a large DC link capacitor. The DC side load current (idc2 ) should be fed forward without any low-pass filtering for proper operation.
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Filter Currents
>> L=0.01;>> R=1;>> Ts=0.00005;>> Rload=50;>> Lload=0.1;>> Tf=10e-3;>> Tidc=9*Tf;>> Kpdc=3*Cdc/Tidc;
0 0.01 0.02 0.03 0.04 0.05-20
0
20ia,load
0 0.01 0.02 0.03 0.04 0.05-10
0
10ia,ActiveFilter
0 0.01 0.02 0.03 0.04 0.05-20
0
20ia,grid
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Spectra
0 0.02 0.04 0.06 0.08 0.1-15
-10
-5
0
5
10
15Original signal (Blue) and resampled signal (Red)
0 200 400 600 8000
2
4
6
8
10
Frequency spectra with 10 Hz resolution
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-20
-10
0
10
20Original signal (Blue) and resampled signal (Red)
0 100 200 300 400 500 600 700 800 900
2
4
6
8
10
Frequency spectra with 10 Hz resolution
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nX. Effects of non-idealities (I)
L Re
i
u
T1 D1
T2 D2
D3 T3
D4 T4
Tp1
Tp2
Tp3
Tp4
CDCVDC
+ vA vB
T4 D3 T4 T4 T4 D3 T4 T4 T4
T1 T1 T1 D2 T1 T1 T1 D2 T1A
B
v
+vtri
-vtri
vA, ref
vB, ref
vA
VDC/2
-VDC/2
vB
VDC/2
-VDC/2
i
VDC
u
t
t
t
t
Note that the semiconductor forward voltage drop affects the output voltageLoss of voltage-time area!
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X. Effects of non-idealities (II)
L Re
i
u
T1 D1
T2 D2
D3 T3
D4 T4
Tp1
Tp2
Tp3
Tp4
CDCVDC
+ vA vB
T4 D3 T4 T4
T1 T1 T1 D2A
B
v
+vtri
-vtri
vA, ref
vB, ref
vA
VDC/2
-VDC/2
vB
VDC/2
-VDC/2
i
VDC
u
t
t
t
t
T4
D2
Note that the blanking time affects the output voltageLoss of voltage-time area!
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X. Effects of non-idealities (III)
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-20
-10
0
10
20
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-400
-200
0
200
400
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500
0
500
Forward Voltage drop: redBlanking Time: green
11 ,uu
au1
cba iii ,,
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X. Effects of non-idealities (IV)
Forward Voltage drop: redBlanking Time: green
u u
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nX. Effects of non-idealities (V)
• The proportional part of the controller is too “weak” to compensate. The only possible way to make it less weak is to increase the gain which would give an oscillatory behaviour
• The integral part act properly only on dc-components and not on dq-reference frame harmonics. To circumvent the last problem, rotating coordinate systems are included also for the frequencies where the harmonics appear.
The three-phase converter controller can not fully compensate for these non-idealities for two reasons:
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More InformationActive Power Line Conditioners are in most cases notcovered in books on power electronics, however:
On the home page of power electronics course:• The Power Electronics Handbook", edited by Timothy L
Skvarenina, CRC-press, 2002, ISBN 0-8493-7336-0.http://www.engnetbase.com/books/447/7336_pdf_toc.pdf
On Per Karlsson’s homepage:• M. Bojrup, (1999), "Advanced Control of Active Filters in a Battery
Charger Application", Licentiate thesis, Department of IndustrialElectrical Engineering and Automation, Lund Institute of Technology,Lund, Sweden, December 1999, ISBN 91-88934-13-6.http://www.iea.lth.se/~ielper/charger/MB-thesis.pdf
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Y. ConclusionsCommercial Semikron three-phase inverter
Suitable also for active power line conditioning!
73 kVA PWM three phase inverter with a long-life DC-link for motor drives
VDC-link = 600 V ± 10 %Voutput = 3 x 420 V (0,05 Hz ... 60 Hz)Inominal = 100 ARMS, Ioverload = 165 ARMS
fswitching = 1,5 kHz
SKiiP 342GD120 - 314 CTVP 16/280 F
9 900 µF / 800 V at DC-link