high-order passive filters for grid-connected voltage ... · introduction • power filters are...
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High-Order Passive Filters for Grid-Connected Voltage-Source
Converters: Topologies and Design Challenges
Remus BeresPhD Fe l low
Dept . o f Energy Techno logyAa lborg Un ivers i t y
rnb@et .aau .dk
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Outline
• Introduction
• Passive Filters Description
• Design Challenges
• Optimum Passive Damping Method
• Conclusions
• Questions
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Introduction
• Power Fi l ters are needed to l ink act ive conver ters wi thideal power sources/ loads
• A high-order f i l ter is adopted usual ly due to s ize and costconsiderat ions
• The aim is to effect ively f i l ter out the swi tch ing harmonicsf rom the act ive conver ter and to ensure VSC operat ion
Switching frequency harmonics Power filter
Converter current Grid current
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Passive Filters Description
Typical Power Fi l ters
• L f i l ter : 20 dB/decade at tenuat ion
• LC f i l ter : 40 dB/decade at tenuat ion
• LCL f i l ter : 60 dB/decade at tenuat ion
Cf
L1 L2
Output current
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Passive Damped Filters Topologies
The key is to ensure h igh eff ic iency, low cost and s ize
There should be no r isk of harmonic ampl i f icat ion wi th the
ut i l i ty gr id
Shunt pass ive damped f i l ters topolog ies
C - t y p e f i l t e r u s e d t o d a m pt h e r e s o n a n c e a n d t h eh i g h f r e q u e n c y r i p p l e ! *
*Beres et al., “Improved Passive Damped LCL Filter to Enhance Stability in Grid-Connected Voltage-Source Converters”,
Proceedings of CIRED, 2015
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Passive Damped Filters Topologies
“More effect ive” passive f i l ter*
FilterPassiveDevice
Peak Rating L/C/RLI2
(HA2)Volume(cm3)
LCL + RC
L1 23 A 1.5 mH
1.06
513 L2 21 A 0.7 mH 200
Cd, Ct 330 V 4.7 µF 22.7 Rd 17 W 17 Ω -
Trap + RC
L1 23 A 1.5 mH
0.89
513 L2 21 A 0.3 mH 100
Cd, Ct 330 V 4.7 µF 22.7 Lt 3 A 0.05 mH 7.6Rd 14 W 13 Ω -
2traps + RC
L1 25 A 0.8 mH
0.59
200 L2 21 A 0.2 mH 100
Cd, Ct 330 V 4.7 µF 22.7 Lt 5 A 0.05 mH 7.6Ct2 330 V 0.44 3.65 Lt2 2.5 A 0.14 mH 7.6 Rd 17 W 7.7 Ω -
Hal f physica l vo lume!
*Beres et al., “Optimal Design of High-Order Passive-Damped Filters for Grid-Connected Applications ”, IEEE Transactions
on Power Electronics, Early Access, 2015
31Total
Total
LC
27Total
Total
LC
8.5Total
Total
LC
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Design Challenges of Passive Filters
Known challenges (physical design)
• Size optimized design/reduced filter cost result in low inductances (high
capacitance) high ripple current in the filter increased power loss
• Loss optimized high-order filters results in increased size of the filter• Accurate models to optimize the passive filter are not ready available
Additional challenges (system level)
• Attenuation of resonance harmonics or limitation of instabilities risks• Damping is more challenging for size optimized filters due to increased
capacitance• Harmonics regulations not explicitly defined above 2 kHz (2-9 kHz
specifications expected soon)
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Design Challenges of Passive Filters
Power Loss in the VSC and Passive Fi l ter
Results from literature
• ~80% of filter loss occurs in the converter side inductance!
[1] K. Park, F. Kieferndorf, U. Drofenik, S. Pettersson, and F. Canales, “Weight minimization of LCL filters for high power converters,” in 2015 9th International Conference on Power Electronics and ECCE Asia (ICPE-ECCE Asia), 2015, pp. 142–149[2] L. Wei, Y. Patel, R. Automation, A. Bradley, and W. E. Drive, “Evaluation of LCL Filter Inductor and Active Front End Rectifier Losses Under Different PWM Method,” pp. 3019–3026, 2013[3] J. Muhlethaler, M. Schweizer, R. Blattmann, J. W. Kolar, and A. Ecklebe, “Optimal Design of LCL Harmonic Filters for Three-Phase PFC Rectifiers,” IEEE Trans. Power Electron., vol. 28, no. 7, pp. 3114–3125, Jul. 2013
Reference Frequency range VSC loss Filter loss Core loss calculation
method Verified
[1] 2~6 kHz 0.8~1.5 % 0.1~0.2 % iGSE –
[2] 2~12 kHz 0.5~1 % 0.3~0.5 % NSE –
[3] 3~12 kHz 0.5~1.2 % 1.2~2.2 % i2GSE+loss map yes
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Power Loss in the Converter Side Inductance
single phase vs three phase
• For a mi of 0.95, the maximum minor loop frequency is 20 fsw!
Permeability dependence of the Fe-Si material simulated in time-domain
Example: 70% inductance decrease at rated current
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Power Loss in the Converter Side Inductance
Ferr i te + Laminated sheets (H 0=0)
0.01
0.1
1
10
100
1000
1 10 100 1000
P cv
(kW
/m3 )
ΔB [mT]
0.01
0.1
1
10
100
1000
5 50 500P c
v(k
W/m
3 )ΔB [mT]
Iron 110µHigh Flux 60µMega Flux 60µMPP 26µSendust 26µ
10 kHz50 kHz100 kHz
Core loss of Fe-Si 10 t imes h igher in laminated sheets !
Powder mater ia l (H 0=0)
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Power Loss in the Converter Side Inductance
Inductor loss character izat ion:
DC-b ias in f luence a t 10 kHz and ∆B=0.09T fo r powder mater ia ls
1
10
100
1000
0 5000 10000 15000 20000
P cv
(kW
/m3 )
H0 [A/m]
• Core loss is not a lways increas ing wi th dc b ias!
• Combina t ion o f the core loss in fo rmat ion and PWM modu la t ion can resu l t i n more s igni f icant opt imizat ion of power loss in the f i l te r !
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1
10
100
1000
500 1500 2500 3500
P cv
(kW
/m3 )
Hm [A/m]
High Flux 60µMega Flux 60µMPP 26µSendust 26µ
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Current Harmonic Limits
Harmonic order h
VDE-AR-N 4105 (LV) BDEW (MV)* IEEE 519
(LV & MV)
5 2.08 2.06 47 1.39 2.84 411 0.69 1.8 213 0.55 1.32 217 0.42 0.76 1.519 0.35 0.62 1.523 0.28 0.42 0.6
(23≤h<35)25 0.21 0.3525 < h < 40 5.2/h 8.67/h 0.3
(35≤h<50)40 < h < 180 6.24/h 6.24/h
Table I: Individual current harmonic limits at PCC* the limits are referred to the low voltage side of the step-up transformer (400 V)
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Current Harmonic Limits
LCL filter design according to IEEE 1547 (series R damper)
• High difference between different harmonic regulations!
• Presence of low harmonics in the grid current needs compensation!
• Lack of damping can result in harmonics limits exceeded around the resonance!
• Alternative passive damping methods are needed to ensure low damping loss!
L1=7%, L2=3%, C=5%, Rd =0.13%, Pd=0.03%, Kp=8.5, Ki=450
L1=4%, L2=3%, C=10%,Rd =0.3%Pd=0.4%, Kp=5, Ki=250
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Optimum Passive Damping Method
Optimum Damping Parameters
• Damping res is to r – used to “ l im i t ” resonance
ins tab i l i t i es in the u t i l i t y g r id . Low or h igh
va lues o f the res is to r have equa l impac t .
• R .D. M idd lebrook deve lop the “ ru les ” fo r
op t imum damping des ign (1978)
• The damping parameters a re dependent on
the charac te r i s t i c parameters o f the f i l te r and
the ra t io (s ) be tween the reac t i ve e lements o f
the f i l t e r (capac i to rs o r induc to rs ) *
d
eq
LaL
d
eq
CnC
0 0, ,eq eqR f f L CResonance frequency can
vary in a wide range!
*Beres et al., “Optimal Design of High-Order Passive-Damped Filters for Grid-Connected Applications ”, IEEE Transactions
on Power Electronics, Early Access, 2015
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Optimum Passive Damping Method
Damping current waveforms
15
RdCf
L1 L2
Shunt RC damper
Cd
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Optimum Passive Damping Method
Half size!
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Damping current waveforms
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Optimum Passive Damping Method
BDEW regulat ions
IEEE 1547 regulat ions
• Pass ive damping loss are reasonable!
• Very h igh resonance at tenuat ion requi res RLC dampers to
l imi t loss!
I1 I2
I1
I2
I1I2 I1 I2
I1 I2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.05 2.85 4.95 10.05 14.95
Dam
ping
loss
es (%
)
Switching frequency (kHz)
I1
I2
I1 I2 I1 I2
0
0.5
1
1.5
2
2.5
1.05 2.85 4.95
Dam
ping
loss
es (%
)
Switching frequency (kHz)
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Optimum Passive Damping Method
BDEW regulat ions
IEEE 1547 regulat ions
• Design rat ings are d i f ferent depending on harmonic
regulat ions, sensor pos i t ion or damping topology
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Summary
• Latest advancements in power filter topologies for grid connected VSC
have been presented
• The optimal design of the filter is related mainly to choice of the converter
side inductance as function of the VSC topology and VSC specifications
• The resonance damping and switching ripple attenuation can be ensured
by shunt passive damped filters
• An optimum design of the passive damped filters was proposed which can
ensure also low damping loss and size
• Further optimization can be performed by considering:• The grid impedance influence on damping and switching harmonics
attenuation• Harmonization between the PWM method and loss in the converter side
inductor
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