Harmonics in Grid-Connected Converters: challenges and cost -effective opportunities in ASD systems
POOYA DAVARI P DA @ E T. A A U . D K
2 0 O C TO B E R 2 0 1 6
WWW.NHTD.ET.AAU.DK
2
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
NHTD has two work-packages based on the harmonic mitigation techniques and solutions as follows: 1- Single Drive Systems 2- Multi Drive Systems MAY 2014 APRIL 2017
NHTD Team
THE PROJECT STRUCTURE:
New Harmonic Reduction Techniques for Motor Drives (NHTD)
Dr. Soltani
Dr. Soltani Prof. Zare
WP2 Leader http://www.nhtd.et.aau.dk
3
Outline
Introduction (three-phase diode front-end)
Electronic Inductor (EI) Concept
Proposed Selective Harmonic Mitigation
Multi-Drive Systems
Experimental Results
Conclusion
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
4
Introduction
Three-Phase Diode Front-End System
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
5 Typical ASD System
Passive Filtering Solution
AC or DC side passive filtering (inductor): simple and effective to some extent. But they are bulky, costly, causes resonance, worsen system dynamic, and etc.
Active harmonic mitigation solutions have been introduced to improve the input current quality. But most of them are complex, costly and reduce system efficiency.
AC or DC side passive filtering After passive filtering (THDi ≈ 40%)
Before passive filtering (THDi > 120%)
ia,n/ia,1
Harmonic order (n)
Simple
Cost effective
Efficient
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
6
Three-Phase Diode Rectifier Passive Filtering Challenges
Typical ASD System
Performance of three-phase diode rectification using dc-side passive filtering: (a) effect of loading condition, (b) corresponding power factor λ and input current THD at different power levels, (c) effect of dc-link inductor size.
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
(a) (b) (c)
7
Three-Phase Diode Rectifier Passive Filtering Challenges
Typical ASD System
Typical annual loading profile of adjustable speed drive applications: (a) water pump, (b) cooling tower.
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
8
Electronic Inductor Concept
Basic Idea
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
9 Electronic Inductor Technique
Basic Concept
Emulating the behavior of an ideal infinite inductor
λ ≈ 0.95
THDi ≈ 29%
THDi and Power Factor (λ) independent of the load profile.
Controlling dc-link (udc).
10 Electronic Inductor Technique
No major modification is imposed to the original system!
ia
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
11
Load Profile
5 A/div, 2 ms/div
Po = 100%
Po = 70%
Po = 50%
Po = 30%
Po = 10%
ia
λ ≈ 0.95
THDia ≈ 29 %
(b)
Cdc
+
_
Ldc
a
b
c
RL udc
D
S
electronic inductor (EI)
Grid
~ia
iL
ur
Udc*
udc
PI
iLiL*
S controller
(a)
Electronic Inductor Concept
Independent performance (10% to 100% Po)
Implementation of electronic inductor using a boost dc-dc converter topology in a three-phase diode rectifier: (a) circuit schematic, (b) corresponding input current waveform (ia) at different power levels. (Simulation parameters: rms line-to-line voltage Ug,LL,rms = 400 V, grid frequency fg = 50 Hz, grid impedance Lg = 0.18 mH, Rg = 0.1Ω , rated power Po,max = 7.5 kW, Udc = 700V, fsw = 40 kHz, dc-link capacitance Cdc = 470 μF, and dc-link inductance Ldc0 = 2 mH.)
Assuring CCM operation
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
12 Experimental Setup
System Specifications
Ug,LL,rms fg Lg, Rg Pomax
(100%)
Udc fsw Ldc0 Cdc
400 V 50 Hz 0.18mH, 0.1 Ω
7.5 kW 700 Vdc 20 kHz 1 mH 470 µF
Employed components
7.5 kW
13 Experimental Results
Original Drive (Passive Filter)
Po = 5kW Udc = 534V
Po = 3kW Udc = 534V
THDi = 48.7%, λ = 0.89
THDi = 67.6%, λ = 0.81
EI (flat current modulation)
L = 1mH, fsw = 20 kHz THDi = 28%, λ = 0.95
THDi = 28%, λ = 0.94
Po = 5kW Udc = 700V
Po = 3kW Udc = 700V
L = 1mH, fsw = 20 kHz
L = 2.5mH
L = 2.5mH
14
Improving Efficiency
Adjustable Switching Frequency Scheme
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
15 Proposed Solutions
Adjustable Switching Frequency
5 A/div, 2 ms/div
Po = 100%
Po = 70%
Po = 50%
Po = 30%
Po = 10%
ia
λ ≈ 0.95
THDia ≈ 29 %
5 A/div, 2 ms/div
Po = 100%
Po = 70%
Po = 50%
Po = 30%
Po = 10%
ia
λ ≈ 0.95
THDia ≈ 29 %
Po (%)
k'ripp
le (%)ƒ'sw
k'ripple (%)
ƒ'sw
(kHz)
[1] P. Davari, Y. Yang, F. Zare, and F. Blaabjerg, “Energy Saving in Three-Phase Diode Rectifiers using Adjustable Switching Frequency Modulation Scheme,” EPE-2016.
16
Adjustable Switching Frequency
System Specs:
Using ASFM strategy improves efficiency from 315W losses to 173W losses (95.8% vs 97.7%)
5 A/div, 2 ms/div
Po = 100%
Po = 70%
Po = 50%
Po = 30%
Po = 10%
ia
λ ≈ 0.95
THDia ≈ 29 %
5 A/div, 2 ms/div
Po = 100%
Po = 70%
Po = 50%
Po = 30%
Po = 10%
ia
λ ≈ 0.95
THDia ≈ 29 %
Proposed Solutions
Po (kW)
η (
%)
Fixed switching-EI, IGBT
with Xflux core @ 35 kHz
Proposed ASFS-EI, IGBT
with Xflux core @ 10-35kHz
Passive filtering
Fixed switching-EI, IGBT
with Xflux core @ 35 kHz
Proposed ASFS-EI, IGBT
with Xflux core @ 10 kHz
Three-phase rectification with: η : Effeciency
T : Power switch (Transistor)
sw : Switching loss
cond : Conduction loss
D : Boost diodegate : Gate-driver
1-λ
THDi
Ploss,total
(%)
(W)
PLdc (W)
Pbridge (W)
PT,sw
PT,cond
PD,sw
PD,cond
Pgate
(W)
(W)
(W)
(W)
(W)kripple(%)
9075
6045
3015
1
2
3
4
5
6
504540353025
0.12
0.1
0.08
0.06
0.04
0.02
60
3040
50
2010
60
50
40
30
20
10
300
250
200
150
100
50
20
18
16
14
12
105
1525
3545
55
160 10130 100 70 40
119
75
31
0.7
0.6
0.5
0.4
0.3
0.2
PC,ESR (W)
C,ESR : DC-Link Capacitor
Effective Series Resistor
Parameter Symbol Value
Grid phase voltage vabc 230 Vrms
Grid frequency fg 50 Hz
Grid impedance Lg, Rg 0.18 mH, 0.1 Ω
DC-link inductor Ldc-p, Ldc 2.5 mH, 2 mH
DC-link capacitor Cdc 470 µF
DC-link voltage Udc-p, Udc ≈ 534V, 700 V
Rate power Po,max (100%) 7.5 kW
17
Using WBG Devices
Applying SiC power devices reduces the size of magnetic components and losses (131 W vs 173 W)
Proposed Solutions
Passive filtering
Fixed switching-EI, IGBT
with Xflux core @ 35 kHz
Proposed ASFS-EI, IGBT
with Xflux core @ 10 kHz
Three-phase rectification with: η : Effeciency
T : Power switch (Transistor)
sw : Switching loss
cond : Conduction loss
D : Boost diodegate : Gate-driver
Passive filtering
Fixed switching-EI, SiC
with Xflux core @ 35 kHz
Fixed switching-EI, SiC with
KoolMu core @ 100 kHz
Three-phase rectification with:
1-λ
THDi
Ploss,total
(%)
(W)
PLdc (W)
Pbridge (W)
PT,sw
PT,cond
PD,sw
PD,cond
Pgate
(W)
(W)
(W)
(W)
(W)kripple(%)
9075
6045
3015
1
2
3
4
5
6
504540353025
0.12
0.1
0.08
0.06
0.04
0.02
60
3040
50
2010
60
50
40
30
20
10
300
250
200
150
100
50
20
18
16
14
12
105
1525
3545
55
160 10130 100 70 40
119
75
31
0.7
0.6
0.5
0.4
0.3
0.2
1-λ
THDi
Ploss,total
(%)
(W)
PLdc (W)
Pbridge (W)
PT,sw
PT,cond
PD,sw
PD,cond
Pgate
(W)
(W)
(W)
(W)
(W)kripple(%)
9075
6045
3015
1
2
3
4
5
6
504540353025
0.12
0.1
0.08
0.06
0.04
0.02
60
3040
50
2010
60
50
40
30
20
10
300
250
200
150
100
50
20
18
16
14
12
105
1525
3545
55
160 10130 100 70 40
119
75
31
0.7
0.6
0.5
0.4
0.3
0.2
(a) (b)PC,ESR (W)
C,ESR : DC-Link Capacitor
Effective Series Resistor
PC,ESR (W)
Ldc = 2 mH Ldc = 1 mH
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
18
Proposed Solutions
Pulse Pattern Modulation
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
19 Proposed Solutions
Pulse Pattern Modulation
[1] P. Davari, F. Zare, and F. Blaabjerg, “Pulse pattern modulated strategy for harmonic current components reduction in three-phase ac-dc converters,” IEEE Trans. Ind. Appl., vol. 52, no. 4, pp. 3182-3192, July-Aug. 2016.
20 Proposed Solutions
Pulse Pattern Modulation
[1] P. Davari, F. Zare, and F. Blaabjerg, “Pulse pattern modulated strategy for harmonic current components reduction in three-phase ac-dc converters,” IEEE Trans. Ind. Appl., vol. 52, no. 4, pp. 3182-3192, July-Aug. 2016.
van
ia
Idc1
-Idc1
-Idc2
Idc2
Idc2
-Idc2
120o
30o
α1
α2
β β 2β
30o ωt
ωt
ωt
ωt
θ θ
2π
2π
2π
2π
π
π
π
π
π/2
Adding or subtracting phase-displaced current levels
21 Proposed Solutions
Pulse Pattern Modulation
[1] P. Davari, F. Zare, and F. Blaabjerg, “Pulse pattern modulated strategy for harmonic current components reduction in three-phase ac-dc converters,” IEEE Trans. Ind. Appl., vol. 52, no. 4, pp. 3182-3192, July-Aug. 2016.
Optimization
1 1(1)
(n)
(1)
a g
g
n n
g
Obj M i L
iObj L
i
2
obj n n nF w Obj L
0 1 2 0
3m
where n = 6k±1 with k being 1, 2, 3, ….
Instead of fully nullifying the distortions, the harmonics could be reduced to acceptable levels by adding suitable constraints (Ln).
Constraint
Objective Function Weighting Factor
Here, Fobj is formed based on a squared error with more flexibility by adding constant weight values (wn) to each squared error function
22 Experimental Setup
Employed components
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
23 Experimental Setup
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
ia
Idc1 2π ωt
ωt
ωt
iM
ib
ic
2π
2π
2π
Idc2
Idc1
Idc2
θ
β
2β
120o
120o
120o
30o
θ Idc2
Idc2
Idc1
Idc1
ωt
30o
2β
+ iM
ia
ib
ic
+
1/2
abs( )
abs( )
abs( )
|sin(3ω0t)|
β β
β
α1 α11
1 11
0
1 2
1
:
( sin(3 ) sin(3 ))
M dc dc
M dc
if t
i I I
else
i I
Synthesis of the modulation signal
1 11
0
1 2
1
:
( sin(3 ) sin(3 ))
M dc dc
M dc
if t
i I I
else
i I
24 Experimental Results
Harmonic Elimination [7th and 13th]
Harmonic Mitigation
Strategy
Harmonic Distribution and THDi (%)
ia (5)/ ia (1) ia(7)/ ia (1) ia(11)/ ia (1) ia (13)/ ia (1) THDi
7th and 13th harmonic
cancellation 31.2 2.3 9.5 1 34
5th, 13th harmonic
cancellation 4.7 37.5 23.4 4 47.7
Conventional method
(square wave) 20 14 8.7 7.3 28.6
Idc1 = 1, Idc2 = 0.618, α1= 42o
Harmonic Elimination [5th, 13th]
Idc1 = 1, Idc2 = 0.653, α1= 70o
Po = 5kW Udc = 700V Po = 5kW Udc = 700V
25
Proposed Solutions
Multi-drive
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
www.weg.net
26 Multi-Drive Configuration
Basic Concept
Generating staircase total input current by proper combination
In many applications it is a common practice to employ parallel connected drive units. In this situation the application demand is met using multiple modestly sized motor units rather than one single large unit.
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
27
Phase-shifted Flat Current Control
Multi-Drive Configuration
[1] Y. Yang, P. Davari, F. Zare, and F. Blaabjerg, “A dc-link modulation scheme with phase-shifted current control for harmonic cancellation in multi-drive applications,” IEEE Trans. Power Electron., vol. 31, no. 3, pp. 1837-1840, Mar. 2016.
28
The new current modulation technique is applied to each DC-DC converter in order to further improve the current quality. However, it requires PLL for synchronization purpose.
Multi-Drive Configuration
[1] P. Davari, Y. Yang, F. Zare, and F. Blaabjerg, “A multi-pulse pattern modulation scheme for harmonic mitigation in three-phase multi-motor drives,” IEEE J. Emerg. Sel. Top. Power Electron., vol. 4, no. 1, pp. 174-185, Mar. 2016.
[2] P. Davari, Y. Yang, F. Zare, and F. Blaabjerg, “Predictive pulse pattern current modulation scheme for harmonic reduction in three-phase multi-drive systems”, IEEE Trans. Ind. Electron, vol. 63, no. 9, pp. 5932-5942, Sept. 2016.
Pulse pattern current modulation
29 Multi-Drive Configuration
Pulse pattern current modulation (αf ≠ 0o)
van
1 2
Idc2Idc1
i1
Idc1
Idc2
Idc2
-Idc1
-Idc2
-Idc2
α1
α0
α2
120o
β 2β
θ 2π π ωt
ωt
ωt
ωt
i1'
i2'
isa
↑
30o
↑
↑
ꜛ ꜛ
αf
ꜛ ꜛ
αf
-Idc1
2π
2π
2π
30o
α0 β
θ
30o
120o
ꜛ
ꜛ
ꜛ
ꜛ
centered
↑ Idc2
2
2
0
1
2
2
0
1
1
1
2 2sin sin 2
3
2 2cos cos 2
3
( 1)
( 1)
dc
n j j
j
dc
n j j
j
j
j
I na n n n
n
I nb n n n
n
1
0 0
1
0 0
2 2sin sin
3
2 2cos cos
3
dc
n
dc
n
I na n n
n
I nb n n
n
2 2
s n n n ni n a a b b
+
+
=
30
Implemented Setup
SCR
Symbol PARAMETER Value
vg,abc Grid phase voltage 230 Vrms
fg Grid frequency 50 Hz
Zg (Lg, Rg) Grid impedance 0.1 mH, 0.01 Ω
Ldc DC link inductor 2 mH
Cdc DC link capacitor 470 µF
Vo Output voltage 700 Vdc
Kp, Ki PI controller (Boost converter) 0.01, 0.1
Kf, ts, ξ PLL parameters 0.8, 0.2 s, 1.41
HB Hysteresis Band 2A
Po_total Total output power ≈6.5 kW
Parameters of the multi-rectifier system
Multi-Drive Configuration
Diode
Rectifier
31 Multi-Drive Configuration
Experimental Results (phase shift control)
THDi ≈ 16%, λ = 0.93
PSCR = 3 kW, PDR = 3.63kW, Udc = 700V
THDi ≈ 15.8%, λ = 0.95
PSCR = 3 kW, PDR = 3.36kW, Udc = 700V
32 Multi-Drive Configuration
THDi ≈ 8.6%, λ = 0.94
PSCR = 3 kW, PDR = 3.65kW, Udc = 700 V
THDi ≈ 10%, λ = 0.94
PSCR = 3 kW, PDR = 3.86kW, Udc = 700 V
Experimental Results (current modulation)
33 Multi-Drive Configuration
Extending number of the units (phase shift control)
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
More flexibility in obtaining desired THDi and PF
Five parallel units (n = 5)
λmax THDi,min
34 Multi-Drive Configuration
Extending number of the units (current modulation)
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
Five parallel units (n = 5)
Lower harmonic distortion can be obtained
λmax THDi,min
35 Multi-Drive Configuration
Experimental Setup
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016
Unit4 Unit3 Unit2 Unit1
ia_PCC THDi = 8.3% λ = 0.92
FFT
ia_DR
ia_SCR_1
ia_SCR_2 ia_SCR_3
36
The EI technique can significantly improve the THDi , λ and stable DC link
The proposed pulse pattern modulation can eliminate low order harmonics
The efficiency of EI technique can be significantly improved by employing WBG devices, alternative topologies and smart control techniques
Conclusion
With multi-drive configuration, the EI technique can further reduce the THDi
The EI technique can maintain the system performance under non-ideal operation conditions (e.g., unbalanced grid)
Harmonics in Grid-Connected Converters | Pooya Davari | 20 Oct, 2016