An improved version of a single phase series resonant converter is suggested as an optimal candidate for mega-watt, kilo-volt DC wind turbines

1. Candidate – Catalin Dincan
Main supervisor – Prof. Philip Kjær
Co-supervisors – Prof. Stig Munk Nielsen, Prof. Claus Leth Bak
Department of Energy Technology, 3rd.sept.2018
HIGH POWER MEDIUM VOLTAGE
DC/DC CONVERTER TECHNOLOGY
FOR DC WIND TURBINES
PH.D. DEFENCE

2. Agenda
Introduction
Application
Main hypotheses and objectives
Selection process
Survey of circuits & demonstrators
Proposed methodology
Selected topology
Topology (SRC#)
Theory
Simulated performance
10 MW Design example
Experiments
Proof of concept exp. (10 kW, 500V/5000V)
Soft-switching exp. with target devices
Conclusions
2www.dcc.et.aau.dk

3. HVAC (300 kVac)
MVAC (66 kVac)
HVDC (± 320 kVdc)
Introduction
Application
A case for HVDC wind farms with MVDC collection network
MVDC ((± 50 kVdc)
HVDC (± 320 kVdc)
3
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How to decrease
cost of technology?

4. Introduction
Application:
Present solution: MVAC + HVDC Future solution: MVDC + HVDC
The new collection concept requires:
1. Turbines with MVDC output
2. DC cables from turbines to HVDC converter
3. MV/HV converter
*P. Kjær, Y. Chen – ECPE workshop 2015
4
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G G G G G G G G G G
AC AC
DC
DC
AC
Onshore substation
HVDC
Submarine
Cable
400kV
400kV
HVDC
±320kVDC
3-Ph. XFMR
400kV/66kV
3-Ph. XFMR
400kV/66kV
66kV 66kV
WT WT WT WT WT WT WT WT WT WT
G G G G G G G G G G
AC
DC
AC
Onshore substation
HVDC
Submarine
Cable
400kV
HVDC
±320kVDC
DC/DC Converter
±320kVDC/
±50kVDC
WT WT WT WT WT WT WT WT WT WT
DC
DC
±50kVDC
DC
DC
±50kVDC
DC/DC Converter
±320kVDC/
±50kVDC

5. Introduction
Application
66kVAC wind
farm
±50kVDC wind
farm
Annual Energy losses
*P. Kjær, Y. Chen – ECPE workshop 2015
1-2% savings on losses
1-2% savings on BoM cost
No dc/dc converter
No experience
5
Meyer: “Key components for future offshore DC grids”, PhD RWTH
Aachen ISEA, 2007
Vulcan, Kjær, Helle, Sahukari, Haj-Maharsi, Singh: ”Cost of Energy Assessment
Methodology for offshore AC and DC wind power plants”, Proceedings of OPTIM,
pp.919-928, Brasov, Romania, May 2012www.dcc.et.aau.dk

6. Introduction
Main objectives
Pn = 5...15MW
Fsw = 0.5...X Khz
Vdc_out = ±35...±50kVdcVdc_in = ±0.5...±8kVdc
1. Identify
2. Design
3. Develop
High power
Medium voltage
DC/DC converter
Unidirectional Galvanic separation High voltage gain
6www.dcc.et.aau.dk
Off-the-shelf tech.
Requirements
optimal circuit
proof of concept
guide line

7. Selection process
Selected wind farm configuration
7www.dcc.et.aau.dk
~G
~
~G
~
~G
~G
~G
~ AC
Grid
Onshore
Substation
HVDC
Offshore
Substation
WTT cluster MVDC
Tomorrow
~G
~G
~G
AC
Grid
HVAC
WTT cluster MVDC
~
~ AC
Grid
Onshore
Substation
HVDC
Offshore
Substation 2
Today
~G
AC
Grid
HVAC
WTT cluster MVAC
~
~G
~
~G
~
~G
Offshore
Substation
1
WTT cluster MVAC
~
Offshore
Substation
1
~

8. Selection process
Turbine converter configuration
~G
1 2
~G
1 2
~G ~
~
1 2 3
~G ~ ~
1 2 3 4
8
Subject of interest!
Highest priorities: Circuit design, semiconductors
Lower priority: Transformer design

9. Selection process
Catalogue of circuits
Reduced Matrix
Full Bridge Matrix
SM SM
SM SM
SM SM
SM SM
SM SM
SM SM
SM
SM
SM
SM
SM
SM
SMSM
SMSM
SMSM
SMSM
SMSM
SMSM
SM
SM
SM
SM
SM
SM
MMC
Cell #1 Cell #2 Cell #N
Cascaded boost
SAB-Single Active Bridge
Dual Active Bridge
L Cs
Series Resonant Converter
LLC Converter
L
Lp
Cs
Jovcic 3phase step up resonant converter
Cell #1 Cell #2 Cell #N
37 topologies
. . . And others!
9
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10. Selection process
Survey of demonstrators
Traction
10
Solid State Transformer
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11. Selection process
Design drivers for DC wind turbines
List of functionalities:
1. Control DC power, voltage current
2. Reliable valve commutation
3. Maintenance
4. Reliability
5. Redundancy
6. Protection
7. EMC/EMI
Etc...
Design drivers:
Availability (rank-5)
Electrical losses (rank-4)
Ratings (rank-3)
Repair costs (rank-2)
Power density (rank-1)
11
AC/DCPMG DC/DC VMVDC
VLVDC
Grid conv. Control
?
Gen. Control
Torque Control DC link Control
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12. www.dcc.et.aau.dk 12
A) C)
> 100 km
Monolithic transformer + rectifer
– Keep low number of components
– Start simple
Selection process
Modularity level
Selected modularity level

13. Introduction
Application
13
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ESTIMATED ONLY FOR CORE SIZE
No longer bulky 50 Hz transformer! Savings in volume, weight!
AcoreA wdg = 2
kw Jrms Bmax
Pt
fsw
Volume
- rated power
kw
Bmax
Jrms
fsw
Pt
- Window utilization factor
- Flux density
- Winding current density
- Excitation frequency

14. Selection process
Proposed methodology
List of studies
Catalogue of circuits
SOA demonstrators
(Traction, SST, DC Wind turbines)
Selected topologies for further comparison
Specifications
Requirements
High power rating, Unidirectionality, High efficiency,
High power density, Galvanic separation, etc
List of Challenges + List of studies
Classic
Matrix
MMC isolated
M2DC non-isolated
High-gain
Single active bridge
Dual active bridge
Resonant
Switched capacitor cell
14www.dcc.et.aau.dk
M1
DC
DC
Steady state
M1
DC
DC
Dynamic
M1
DC
DC
Fault
M1
DC
DC
Short circuit
M1
DC
DC
Harmonics
List of studies
Sensitivity studies
Spice Spice Spice Plecs
M2 M3 M4 M5
FEM-thermal FEM-thermal
Ploss.diode
Ploss.IGBT
Ploss.trafo
PLECS
M6 M7 M8
Thermal studies
FEM-electric FEM-electric
Electrostatic/Electromagnetic
studies
M9 M10

15. Selection process
Turbine converter circuit specification is found from collector
network use cases (short circuit, surge, transients…)
15
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
F1 F2 F3 F4 F6 F7 D3
0
10
20
30
40
50
60
F1 F2 F3 F4 F6 F7 D3
Turbine circuit: DC capacitor voltage
Turbine circuit: Peak reactor current
x Vnom
x Inom
Simulation study results: overview of component loads
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Output reactor value

16. Selection process
Proposed methodology
16www.dcc.et.aau.dk
Failure mode effect analysis
Data of
analysis
Team of
experts
Failure,
Effects,
Causes
Asses
criticality
assesment
Risk
mitigations
Actions
Effectivnes
analysis
Concept selection
with Pugh matrix
Enter current baseline
design
FULL Bridge converter
List optional concepts:
SAB
LLC
SRC
SRC#
List key design criterion
Availability
Losses
Ratings/Cost
Repair costs
Power density
Determine criterion
weight
Availability - 5
Losses - 4
Ratings/Cost - 3
Repair costs - 2
Power density - 1
Sum the scores for each
concept
Select best concept

17. Selection process
Circuits downselection
• From 37 topologies, down-select to 5 topologies
• Characteristics: single phase, unidirectional, galvanic separation, monolithic
transformer
17
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18. Selection process
Hard-switched Full-bridge converter
18
Vgip
im
t
Pon
Poff
Full bridge converter - FB
Vg
is
ip
L

19. Selection process
Single active bridge
19
Single active bridge - SAB
Vg
is
ip 5
ip
im
Vg
t
Poff
L

20. Selection process
Impact of transformer non-idealities
Vp
Vs
Vp
Vs
Lm
Rm
LlkpRp RsLlks
Cp CsVp Vs
20www.dcc.et.aau.dk
AC
DC
Lm
Rm
LlkpRp RsLlks
ESR
RIGBT
ESR
Cr Lr
Cp
Cs
DC
AC
Transformer non-idealities – part of the resonant tank!
Issues with medium frequency/ high turns ratio transformers
Impact on
hard-switched rectifier

21. Selection process
Open loop – constant frequency LLC
21
Vg
is
ip
LLC converter, operated with constant frequency
ip im
Vg
No control possibility!
Soft-switching capability!
L C

22. Selection process
Open loop – constant frequency LLC
22
How to control a high power, medium voltage resonant converter ?
(a) Sub-resonant DCM
Vg
irp
Tr/2
Tsw/2
Fsw < Fr
Frequency control
Vg
irp
Tsw/2
ΦTr/2
Fsw > Fr
(a) Super-resonant DCM
Phase shift control
Fsw > Fr
a) Phase shift super-resonant (b) Phase shift sub-resonant
ΦTr/2
Tsw/2
Vg
irp
ΦTr/2
Tsw/2
Vg
irp
Fsw > Fr
Fsw < Fr
a) Dual control sub-resonant b)Dual control super-resonant
Vg
irp
Tsw/2
ΦTr/2
Vg
irp
Tsw/2
Tr/2
Fsw > Fr
Dual control

23. Selection process
Variable frequency Series Resonant Converter
23
Vg
is
ip
x
Φm
x
Animation
L C
Pn
Fsw
10MW
1MW
100Hz 1000Hz
Pout_avg
+Vg
-Vg
0
ir
im
t
t
t
Φm
x

24. Selection process
Series resonant converter with
Pulse Removal technique
24
Vg
is
ip
Series resonant converter with pulse removal technique – SRC#
x
Φm
Animation
L C Pn
Fsw
10MW
1MW
100Hz 1000Hz
im
is Vg Low power
im
is
Vg
Rated power
Possibillity to control power
Medium frequency transformer design
Soft-switching capability

25. Selection process
Classic SRC vs. SRC#
25
LIMITED OPERATIONAL RANGE
UP TO 6% LOSSES, DUE TO BULKY TRANSFORMER
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26. Selection process
Selected topology – SRC#
26
SRC-series resonant converter
Foil
SRC#
Cover basic
design options!
´
Off-the-shelf technology
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27. Topology – SRC#
Device waveforms
ZVS
Low
Turn-Off
Current
Vce Ice
S1
ZVS ZCS
D5
VdId
27www.dcc.et.aau.dk
S1 S3
S2 S4
D5 D7
D6 D8
S1 S3
S2 S4
D5 D7
D6 D8
Soft-switching  higher efficiency

28. Topology – SRC#
Modes of operation
28
V’G(t)
irs(t)
t
DC
AC
AC
DC
V’G
irs
VoutVin
t
V’G(t)
irs(t)
V’G(t)
irs(t)
t
t
V’G(t)
irs(t)
1 p.u. = 10 MW
0
0.5
1.0
1.5
2.0
2.5
3.0
Power[p.u] Fsw [Hz]
100 200 300 400 500 600 700 800 900 1000
DCM1
𝐏𝐨𝐮𝐭 = 𝟒 ∙ 𝐅𝐬𝐰 ∙ 𝐍 ∙ 𝐂 𝐫 ∙ 𝐕𝐢𝐧 ∙ 𝐕𝐨𝐮𝐭
DCM1
DCM2
CCM1-Hybrid
CCM1
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29. Topology – SRC#
Voltage sharing in medium voltage diode valve
Rg
Cs
Rs
29
Line frequency diode
- cheap, robust, low cond. loss
”Characterization of diode valve in medium voltage dc/dc converter for wind turbines”, C. Dincan, P.C.Kjær, Proc. IEEE Eur. Conf.
Pow. Electron. And Appl. (EPE2016), Sept. 2016
Mineral oil
Diode Grading
resistor
RC
Snubber
Thermal
switch
Voltage
divider
Mineral oil
Metalic enclosure

30. Topology – SRC#
Voltage sharing in medium voltage diode valve
Rg
Cs
Rs
• R e v e r s e r e c o v e r y c h a r g e v a r i a t i o n
30
± 5%ΔQrr => ± 45% ΔV
Line frequency diode
- cheap, robust, low cond. loss
”Characterization of diode valve in medium voltage dc/dc converter for wind turbines”, C. Dincan, P.C.Kjær, Proc. IEEE Eur. Conf.
Pow. Electron. And Appl. (EPE2016), Sept. 2016
± 10%ΔCs => ± 10% ΔV
• s n u b b e r c a p a c i t o r v a r i a t i o n

31. Topology – SRC#
Line frequency diodes
31
irp
im irs
Tr/2
Tsw/2
TH
t[s]
If[A]
If[A]
Time[s] Time[s]
TH
Fsw,max
TH ≈20 us
TH < 0.2
2
Fsw,max ≈ 5 kHz
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32. Topology – SRC#
Controller architecture
Pref
fsw
ΔV
PLANT
LPF
(CL FILTER)
Pref
Vin
fsw Io Ifil
Vo Vfil
FeedForward
Control
Modulator
Gate
pulses
PWMD=50%
Average
Calc.
+
+DIGITAL PI
COMPENSATOR+-
..
Iref Ierr
Io,avg
IoIo,avg
fsw,FFfsw,CPref
Gain scheduled
fsw
Average
Calc.
Vo,avg Vo
Vo,avg
32www.dcc.et.aau.dk
1.1
1 p.u. = 10 MW
0
0.5
1.0
1.5
2.0
2.5
3.0
Power[p.u]
Fsw [Hz]
100 200 300 400 500 600 700 800 900 1000
ΔV=10%
Turbine nominal power
Output power Pout
” Control aspects for a high power, resonant converter for DC wind turbines”, A. Tonellotto, E. Sarra, C. Dincan, P.C. Kjær, S.M. Nielsen, C.L.Bak,
Trans. In Power Electronics and Applic., under review.
Basic controller structure –to operate at steady state operation

33. Topology – SRC#
10 MW design example
LV power
Stacks
Mineral Oil/Ester
Water+Glycol
a) b)
MV valve
Mineral Oil/Ester
c) d)
Natural air cooling
33www.dcc.et.aau.dk

34. Topology – SRC#
Semiconductor and cooling technologies
Inverter: 4 x 4 IGBTs (6.5kV x 750A)
Heat sink with water
cooling
Power Module
+ Gate Driver
DC-link caps
Bus bar
a) b)
Volume = 0.42 m^3
For 3 parallel inverters
Forced fan cooling
1400mm
500mm
200mm
Metalic enclosure
Heat sink with holes
Mineral oil RC Snubber
Press-Pack Diode
Selected diode:
5SDD 06D6000
150mm
600mm
150m
m
900mm
900m
m
900mm
Volume ≈0.73 m^3
60mm
Device 6500 V x 750 A
(FZ750R65KE3)
Number of devices 3 x 4
Total loss 0.27%
Inverter Rectifier
Device 6500 V x 750 A
(5SDD 06D6000)
Number of devices 4 x 40
Total loss 0.4%
34www.dcc.et.aau.dk

35. Topology – SRC#
MF transformer
Core material Amorphous
Flux density 1.5 T
Core material Metglas
2605SA1
Turns ratio 25
Mag. Inductance 10 mH
Sec. Leak. Inductance 78 mH
Core mass 800 kg
Windings mass 380 kg
Total losses 0.2%
Medium frequency Transformer
35
1400
1000
160
160
950
70
510
730
510
16,00
335
160
700
Primarywinding
Secondarywinding
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
Volume ≈ 0.72 m^3
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36. Topology – SRC#
Resonant and output capacitor bank
240 capacitors
Volume ≈ 0.1 m^3
750 capacitors
Volume ≈ 0.1 m^3
60mm
90 mm
50 mm
65mm
C = 15 uF
Vdc = 2200 V
Irms = 45 A
C = 7.5 uF
Vdc = 1800 V
Irms = 20 Aa) b)
Cr 250 nF
LC tank losses 0.28%
Total number of
capacitors
240
Energy 1.25 kJ
Cout 50 uF
Current ripple 1%
Total number of
capacitors
400
Energy 250 kJ (τ = 25ms)
Resonant capacitor bank
36
Output
capacitor
bank

37. Topology – SRC#
Estimated volume
6m
2.5m
2.6m
Rectifier
Output
DC-link
MF
Transformer
3 x
Inverters
0.73m1.6m
0.42m
3
3
3
1.4m
1.4m
0.92m
1.12m1.12m
1.12m 0.92m
0.92m
0.7m 0.5m
0.6m
0.72m
3
3300 mm
1900
m
m
3450mm
Total volume ≈ 22 m^3
DC
DC
Total volume ≈ 3.55 m^3
a) b)
22 m 3.5 m
50 Hz XFRM DC/DC
3 3
≈ 6x
37

38. Experiments
Challenges and strategy of testing at MV level
Medium Voltage Laboratory
Inverter
Rectifier
10kW Load
(≈2500Ω)
5000V
DC Source
Transformer
+
Resonant tank
DSP
500V
DC source
Behind the wall
From 500V
DC Source
Ground stick
Connection
DSP
Driver
DriverDriver
Driver
+5V+15V
A
VV
A
Inverter
Rectifier MVDC Network
Transformer
+
Resonant Tank
5000V500V
POWER
ROOM
CONTROL
ROOM
Control and
communication
Internet
connection
Remote Analog Control
+10V
10kW,500V to 5000V
dc/dc resonant converter
Testing methodology
1. Strategy of testing? – power circulation, source-sink, etc?
2. Number of iteration?
3. How to solve as much as possible with one experiment?
MV experiments
1. Safety issues (medium voltage testing)
2. Responsability
3. Proper training
38

39. Experiments
Proof of concept (10 kW, 500V/5000V)
39” Design of a high power, resonant converter for DC wind turbines”, C. Dincan, P.C.Kjaer, Y. Chen, S.M.Nielsen, C.L.Bak, E. Sarra, V.
Sriram - Trans. In Power Electronics and Applic., under review

40. Experiments
Proof of concept (10 kW, 500V/5000V)
40www.dcc.et.aau.dk
irp – primary resonant current
irs – secondary resonant currentVg – inverter output voltage
Vout – output voltage ripple
≈ 5000 Vdc !
Animation

41. Experiments
Measurement of losses
41www.dcc.et.aau.dk
Iin Vin
Iout Vout
Iin Vin
Input power
Ice
Vce
Id
Vd
Iout Vout
Output power
Ice Vce
IGBT
Id Vd
DIODE

42. Experiments
Proof of concept (10 kW, 500V/5000V)
42
IGBT –
25% utilization
Diode –
25% utilization
Poor design of LrHand
Winded

43. Topology – SRC#
Proof of concept (10 kW, 500V/5000V)
A
50kΩ
1uF
Voltage sharing in medium voltage diode valve
43www.dcc.et.aau.dk
2.5 kV
Vrrm = 1.6 kV

44. Topology – SRC#
Proof of concept (10 kW, 500V/5000V)
kΩ
A
1.0nF
250
b)
Voltage sharing in medium voltage diode valve
44www.dcc.et.aau.dk

45. Experiments
Soft-switching exp. with target devices
Vin
Cin
Cr=100uFLr=180uH
1:1
Cout Vout
A
Vce
Vd
Heating element Heating element
A
V
Output capacitor is charged from the
SRC# and not from the input source
T1
T2
T3
T4
T5
irp irs
Vgice id
D5 D7
D6
D8
R
R
Input
DC-link
Resonant
caps.
Input
DC-link
Rectifier
Full bridge
inverter
Vin
Input source
MF
Transformer
45
”Soft-switching characterization of medium voltage IGBT power modules and press-pack diodes in a 1 kHz mega-watt dc/dc
resonant converter”, C. Dincan, P.C.Kjær, S.M. Nielsen, C.L. Bak, Proc. IEEE Eur. Conf. Pow. Electron. And Appl. (EPE2018)
Vin 4000V
Vout 1000V-4000V
Cin 101 uF
Cout 106 uF
Lm 55 mH
Lr 180 uH
IGBT 6.5 kV/0.75 kA
Diodes 6.5 kV/0.75 kA

46. Experiments
Soft-switching exp. with target devices
46
Principle of operation
Vin
Vout
PWM
Vg
IrpIrp very
small
t0 t1 t2 t3 t4

47. Experiments
Soft-switching exp. with target devices
Fsw = 800 Hz
Fsw = 300 Hz
47

48. Experiments
IGBT losses
T2-experiment
48
T2-simulation T5-experiment
Pon PcondPoff
Vin
Cin
Cr=100uFLr=180uH
1:1
Cout Vout
A
Vce
Vd
Heating element Heating element
A
V
Output capacitor is charged from the
SRC# and not from the input source
T1
T2
T3
T4
T5
irp irs
Vgice id
D5 D7
D6
D8
R
R
HV fiber optic isolated probe
HV probe HV probe
LEM current sensor
Effect of
parasitic
inductance

49. Experiments
IGBT losses
Turn-on process Turn-off process
Turn-off losses
Gate signal
-10V
+19V
Turn-on losses
-10V
+19V
Eon=8[mJ]Pon=8[W]
Fsw=1000Hz
Poff=30[W] Eoff=30[mJ]
www.dcc.et.aau.dk 49

50. Experiments
DIODE losses
D6-exp D6-sim
Vin
Cin
Cr=100uFLr=180uH
1:1
Cout Vout
A
Vce
Vd
Heating element Heating element
A
V
Output capacitor is charged from the
SRC# and not from the input source
T1
T2
T3
T4
T5
irp irs
Vgice id
D5 D7
D6
D8
R
R
HV fiber optic isolated probe
HV probe HV probe
LEM current sensor
D6-exp – forward voltage drop
Pon PcondPrev
X sub-interval!
Reverse
Recovery
Effect of
parasitic
inductance
50

51. Experiments
DIODE losses
Reverse
recovery losses
Erev = 4700[mJ]
Eon = 0[mJ]
Prev = 4700[kW]
Pon 4700[kW]Turn on
losses
51
Pon = 0 [W]
Prev = 4700 [W]

52. Experiments
Measured losses on soft-switching setup
52
Losses per device!
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53. Experiments
Predicted losses on 10 MW example
53
Inverter
losses
0.27%
Rectifier
losses
0.41%
Inverter
losses
0.24%
Rectifier
losses
0.78%
Pn = 10MW
(theoretical example)
Pn ≈ 2.8MW;
average power during one pulse with Fsw = 1000 Hz
Target diode
Qrr = 2000 uC
Lab diode
Qrr = 10000 uC

54. Experiments
Soft-switching exp. with target devices
54
Confidence in semiconductor model is high!
?
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55. Conclusions
Summary
55www.dcc.et.aau.dk
G AC
DC DC
AC
MVAC
G AC
DC DC
AC
MVDC
AC
DC
3%
1.5%
≈6 lower volume
o A high power, medium voltage, resonant DC/DC converter (SRC#) has
been proposed for MVDC application
o Medium voltage experiments have been performed and technology
readiness level has been increased

56. Conclusions
Main contributions
• A new modulation scheme introduced for a single-phase series resonant
converter
• A new converter philosophy for DC wind turbine application was proposed
• Circuit conduction modes identified
• Increased technology readiness level to TRL4 with experimental proof of
concept
• Validation of semiconductor loss model
• Novel soft-switching characterization setup introduced
• A closed loop control architecture was proposed and validated
• A design guide line for the SRC# is proposed
56www.dcc.et.aau.dk

57. Conclusions
Outlook and future work challenges
• Increase technology readiness level to TRL6-7, through the completion
of a thermal concept (0.2 MW and ± 10kV)
• Transformer loss model validation
10 kW/ ± 2.5 kVdc
0.2 MW/ ± 2.5 kVdc
0.2 MW/ ± 10 kVdc
2 MW/ ± 10 kVdc
> 10 MW/ ± 50 kVdc
Proof of
principle
Proof of
concept
Proof of
concept
(thermal)
Product
development
TRL 3-4 TRL 6 TRL 7 TRL 8-9
Ccc
PccPs PpTa
Pce
CpCs
Cce
TccTpTs
Tce
c
Rth
Rthcp
Rthps
Rthwa
Rthca
57

59. Draft Material
59www.dcc.et.aau.dk

60. List of publications
1. ”High power, medium voltage, series resonant converter for DC wind turbines”, C. Dincan, P.C.Kjaer, Y. Chen, S.M.Nielsen, C.L.Bak-
Trans. In Power Electronics and Applic., sept. 2018
2. ”Analysis of a high power, resonant DC-DC converter for DC wind turbines”, C. Dincan, P.C.Kjaer, Y. Chen, S.M.Nielsen, C.L.Bak-
Trans. In Power Electronics and Applic., sept. 2018
3. ” Design of a high power, resonant converter for DC wind turbines”, C. Dincan, P.C.Kjaer, Y. Chen, S.M.Nielsen, C.L.Bak, E. Sarra,
V. Sriram - Trans. In Power Electronics and Applic., under review.
4. ” Control aspects for a high power, resonant converter for DC wind turbines”, A. Tonellotto, E. Sarra, C. Dincan, P.C. Kjær, S.M.
Nielsen, C.L.Bak, Trans. In Power Electronics and Applic., under review.
5. ”Soft-switching characterization of medium voltage IGBT power modules and press-pack diodes in a 1 kHz mega-watt dc/dc resonant
converter”, C. Dincan, P.C.Kjær, S.M. Nielsen, C.L. Bak, Proc. IEEE Eur. Conf. Pow. Electron. And Appl. (EPE2018)
6. ”Analysis and design of a series resonant converter with wide operating range and minimized transformer ratings”, C. Dincan,
P.C.Kjær, Y. Chen, S.M. Nielsen, C.L. Bak, Proc. IEEE Eur. Conf. Pow. Electron. And Appl. (EPE2017)
7. ”Selection of DC/DC converter for offshore wind farm with MVDC power collection”, C. Dincan, P.C.Kjær, Y. Chen, S.M. Nielsen, C.L.
Bak, Proc. IEEE Eur. Conf. Pow. Electron. And Appl. (EPE2017)
8. ”Establishment of functional requirements to DC-connected wind turbine and their use in concept selection”, C. Dincan, P.C.Kjær, Y.
Chen, S.M. Nielsen, C.L. Bak, Proc. IEEE Int. Conf. On DC. Microgrids (ICDCM), June-2017
9. ”Characterization of diode valve in medium voltage dc/dc converter for wind turbines”, C. Dincan, P.C.Kjær, Proc. IEEE Eur. Conf.
Pow. Electron. And Appl. (EPE2016), Sept. 2016
10. ”Control and modulation for loss minimization for dc/dc converter for wind turbines”, C. Dincan, P.C.Kjær, Proc. PCIM, May. 2016
11. ”DC-DC converter and DC-DC conversion method”’, European Patent Application, no. 70059, Filed March, 2017.
60www.dcc.et.aau.dk

61. Draft material
SRC# modes of operation
a) DCM1
V’G(t)
T1 X T2 X
irs(t)
t
irp(t)
VG(t)
im(t)
VCr(t)
b) DCM2
t
V’G(t)
irs(t)
T1 Q1 X T2 Q2 X
t
VG(t)
irp(t)
im(t)
VCr(t)
c) CCM1-hybrid
Q1T1 T2 Q2X X
V’G(t)
irs(t)
t
VG(t)
irp(t)
t
VCr(t)
im(t)
d) CCM1
t
T1 Q1 T2 Q2D1 D2
V’G(t)
irs(t)
t
VG(t)
irp(t)
VCr(t)
im(t)
VCr
irs
T1 T1
T2T2
VCr
irs
T1
Q1
Q2
T1
T2T2
VCr
irs
T1
Q1
Q2
T1
T2T2
VCr
irs
T1
Q1
Q2
T1
T2T2
D1
D2
61
”Analysis of a high power, resonant DC-DC converter for DC wind turbines”, C. Dincan, P.C.Kjaer, Y. Chen, S.M.Nielsen, C.L.Bak-
Trans. In Power Electronics and Applic., sept. 2018
www.dcc.et.aau.dk

62. Draft material
Design guide line
SRC# converter specification: (Table I)
Pin=Pin_min...Pin_max;
Vin=Vin_min...Vin_max;
Vout=Vout_min...Vout_max
Component
library
1. Device
selection
Inverter Transformer
Trade off
cost/
losses?
LC Tank Rectifier
2. Basic electric
design
Nb.of parallel
inverters and
devices
3. Loss model
4. Physical layout
Vol, Weight, Loss,
Cost, Utilization
1. Core and
winding selection
2. Determine
physical layout
3. Determine
transformer
elements
Rp, Rs, Lleak, Cw
Lleak≤Lr
4. Loss model
5. Physical layout
Trade off
cost/
losses?
Vol, Weight, Loss,
Cost, Utilization
1. Capacitor
selection
3. Basic electric
design
Nb.of caps
4. Loss model
5. Physical layout
2. If Lleak = Lr, no
Lr
Trade off
cost/
losses?
Vol, Weight, Loss,
Cost, Utilization
1. Device
selection
2. Basic electric
design/
Nb.of diodes
Snubber design
3. Loss model
4. Physical layout
5. Determine
parasitic elements
Trade off
cost/
losses?
Vol, Weight, Loss,
Cost, Utilization
Voltage
distribution?
Vs. Freq.
Sweep?
ΣCostΣLoss ΣBomΣVol
Optimisation
Selection of Fsw and Fr (Fsw ≤ Fr ε [500...5000] Hz)
Calculate LC tank parameters C = ...Eq(?) L = ...Eq(?)
SRC# model: mode of operation and sensitivity studies
Steady state and worst case scenario waveforms
Transistor
data base
Transformer
data base
Diode data
base
Capacitors
selection
Cooling
system
Step 2. Sub-systems ratings
DC Link bank
1. Capacitor
selection
3. Basic electric
design
Nb.of caps
4. Loss model
5. Physical layout
2. If Lleak = Lr, no
Lr
Trade off
cost/
losses?
Vol, Weight, Loss,
Cost, Utilization
Step 3. Losses and temp.
Step 4. Volume and mass
Step 1. Converter ratings
Input specifications
Select design parameters
Technology selection
62
www.dcc.et.aau.dk

63. Draft material
Simulation, design and analysis tools
63www.dcc.et.aau.dk
Plecs Simulation model
Matlab analytical model
Matlab Transformer design tool

64. Experiments
Other performed experiments
AC
programmable
source
1000hz
D1
Iprim
V Vinv Load
1:6
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
Experiment 1 (10kW,300V/2500V,1000Hz)
Goal: Quantify spread
between diode dynamic
voltage sharing after turn-off
to determine necessary
voltage design margin.
• Reverse recovery charge variation
12kW
AC programmable
source
500-1000Hz
64www.dcc.et.aau.dk
1kHz transformer2.5kV rectifier

65. Experiments
Other performed experiments
Experiment 2 (1kW,250V/500V,1000Hz)
Lr Cr
Vin
T1 T3
T2 T4
D5
D7
D9
D8
D1 D3
D2 D4
Vout
Lm
[ir]
irp irs
im
Cin
Cin
Cf
Cf
iout
RLoad
D6 D10
D11
D12
Goal: Demonstrate circuit and control
functionality
65www.dcc.et.aau.dk

66. Draft material
Loss model
Semiconductor loss model Transformer loss model
I[A]
PcondPcond = aI+bI
2
Psw
Pon
Poff
Prev
AVG
Psw = cI+dI
2
Pinverter
Prectifier
Device
Current
Vmes
Vnom
AVG
Detect
switching
event
I[A]
D[0..0.5]
IGSEFsw[Hz]
B[T]
Mfe[kg]
W/kg Pcore
Winding
current
Winding Rac
Pwindings
Ptransformer
FFT
Rdc
Skin effect
Proximity effectNlayers
Nturns
MLT
Irmsh
RACh
66www.dcc.et.aau.dk

67. Draft material
MF transformer prototypes
10 kW, 500V/5000V, 1kHz 100 kW, 4000V/4000V, 1kHz
67www.dcc.et.aau.dk

68. Draft material
MF transformer prototypes
68www.dcc.et.aau.dk
51,00
132,00
16,00
120,00
51,00
120,00
16,00
152,00
96,0
FoilFoil
FoilFoil
21,5
51,00
120,00
16,00
152,00
LitzFoil
21,5
51,00
120,00
16,00
152,00
RoundFoil
21,5
16,00 16,00
51,00
120,00
16,00
152,00
RoundFoil
21,5
a) V1 b) V2 c) V3 d) V4 e) V5
58,00
8,00
120,00
16,00
152,00
13,00
8,00
21,5
60,00
100,00
68,00
16,00
25,00
80,45
10,00
50,25
15,00
51,00
120,00
16,00
152,00
FoilFoil
21,5
16,00
58,00
V7
8,00
120,00
16,00
152,00
13,00
8,00
58,00
8,00
120,00
16,00
152,00
13,00
8,00
Foil
Foil
Foil
Foil
Litz
Litz
Foil
Foil
Foil
Foil
Round
Round
58,00
8,00
120,00
16,00
152,00
13,00
8,00
Foil
Foil
Foil
Foil
21,5
21,5 21,5 21,5
Foil Foil
Foil
Foil
f) V6
g) V7 h) V8 i) V9 i) V10 i) V11 i) V12
Unit: cm
Different prototypes have been investigated with the team from NTU Singapore

69. Draft material
MF transformer prototypes
69www.dcc.et.aau.dk
0
20000
40000
60000
80000
100000
120000
1 2 3 4 5 6 7 8 9 10 11 12
Winding losses
Core losses
Powerloss[W]
Total loss [W]
V2 V3 V4 V5 V6 V7 V8 V9 V10 V11V1
C.core
Amorphous
Foil/Litz
C.core
Amorphous
Foil/Round
C.core
Silicon Iron
Foil/Foil
Shell.core
Amorphous
Foil/Foil
Shell.core
Amorphous
Foil/Litz
Shell.core
Amorphous
Foil/Round
Shell.core
Silicon Iron
Foil/Foil
C.core
Amorphous
Foil/Foil
C.core
Amorphous
Foil/Foil
C.core
Amorphous
Foil/Foil
10x!
10x!
C.core
Amorphous
Foil/Foil
V12
C.core
Nanocrystalline
Foil/Foil
Lm 4x
smaller
Different prototypes have been investigated with the team from NTU Singapore

70. Draft material
MF transformer prototypes
70www.dcc.et.aau.dk
Design variation V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 Unit
A 510 510 510 510 510 580 580 580 580 600 510 250 mm
B 1320 1520 1520 1520 1520 1520 1520 1520 1520 1000 1520 800 mm
C 160 160 160 160 160 80 80 80 80 160 160 100 mm
D 1200 1200 1200 1200 1200 1200 1200 1200 1200 680 1200 500 mm
E 0 0 0 0 0 160 160 160 160 0 0 0 mm
T 213 213 213 213 213 213 213 213 213 213 213 150 mm
Table 3: Core geometry
Table 4: Core property
Design variation V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 Unit
Type Foil Foil Foil Foil Foil Foil Foil Foil Foil Foil Foil Foil -
Material Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper -
Width 1 1 1 1 1 1 1 1 1 1 1 0,8 mm
Heigh 950 950 950 950 950 950 950 950 950 650 950 475 mm
Area 950 950 950 950 950 950 950 950 950 650 950 380 mm^2
Table 5: Primary wire property
Design variation V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 Unit
Type Foil Foil Litz Round Foil Foil Litz Round Foil Foil Foil Foil -
Material Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper Copper -
Width 1 1 8,12 7,35 1 1 1 7,35 1 1 1 0,8 mm
Heigh 38 38 8,12 7,35 38 38 38 7,35 38 38 38 20 mm
Area 38 38 21 0,51 38 38 21 42,42 38 38 38 16 mm^2
Table 6: Secondary wire property
Design variation V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 Unit
Type C-core C-core C-core C-core C-core Shell Shell Shell Shell C-core C-core C-core -
Material Amorphous Amorphous Amorphous Amorphous Silicon Iron Amorphous Amorphous Amorphous Silicon Iron Amorphous Amorphous Nanocrystalline -
Area 280 280 280 280 280 280 280 280 280 280 280 116 cm^2
Volume 94827 116550 116553 116553 116553 121234 121234 121234 121234 87244 116533 26250 cm^3
Area product 777000 777024 777024 777024 777024 1063296 1063296 1063296 1063296 648883 777024 37500 cm^4
Weight 746 917 917 917 917 954 954 954 954 687 917 207 kg
Table 10: Design performance
Design variation V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 Unit
Flux density 1,58 0,78 0,78 0,78 0,78 0,78 0,78 0,78 0,78 0,78 0,76 0,97 T
Core loss 9481 3474 3474 3474 22000 3600 3600 3600 24000 10000 3310 8473 W
DC Winding loss 6849 14750 20990 154000 14750 16173 23800 15400 14750 - 15000 6569 W
AC Winding loss 11271 51168 55138 711000 51168 56131 60700 982000 51168 11000 54000 32000 W
Total loss 20752 54600 58612 714911 73168 59728 64400 985600 75168 21000 57300 40500 W
Efficiency 99,79 99,45 99,41 93,32 99,26832 99,4 99,36 91 99,24832 99.79 99,42 99,59 %

71. Draft material
Controller architecture
71www.dcc.et.aau.dk
” Control aspects for a high power, resonant converter for DC wind turbines”, A. Tonellotto, E. Sarra, C. Dincan, P.C. Kjær, S.M. Nielsen, C.L.Bak,
Trans. In Power Electronics and Applic., under review.

72. Draft material
Example-Protection during unintended trip
72www.dcc.et.aau.dk

73. Draft material
SRC# model with non-idealities included
73www.dcc.et.aau.dk
a)
b)
c)
d)
e)
f)
Qrr
RC
Qrr
Cp,Cs
Qrr
Lm
Rp,Rs
Rp,Rs
Cr Lr
Rp Rs Cr Lr
Lm
Rm
LlkpRp RsLlks Cr Lr
Lm
Rm
LlkpRp RsLlks Cr Lr
Qrr
Lm
Rm
LlkpRp RsLlks Cr Lr
Qrr
Csn
Rsn
Lm
Rm
LlkpRp RsLlks Cr Lr
Cp Cs
Qrr
Csn
Rsn
f)
irp
irp
Fsw=500 Hz
Fsw=900 Hz
10kW, 500V/5000V recorded waveforms vs. PLECs model

74. Selection process
Proposed methodology
74www.dcc.et.aau.dk
FMEA – Failure mode effect analysis
Data of
analysis
Team of
experts
Failure,
Effects,
Causes
Asses
criticality
assesment
Risk
mitigations
Actions
Effectivnes
analysis
FMEA procedure
1.System to sub-system decomposition
4. Classify levels of severity, occurence and detection
numbers for every sub-system failure mode.
2. Determine function for every sub-system
3. Determine failure mode, root cause and effects
Identify
likelihood of
failure
Occurence
Identify
severity
of failure
mode
Identify
likelyhood
of
detection
5.Calculate
RPN
Risk priority
Number
6.Identify
sub-systems
with highest
RPN

75. Selection process
Proposed methodology
75www.dcc.et.aau.dk
Careful at the Inverter!
Regardless of topology
RPN – risk priority number
”Establishment of functional requirements to DC-connected wind turbine and their use in concept selection”, C. Dincan,
P.C.Kjær, Y. Chen, S.M. Nielsen, C.L. Bak, Proc. IEEE Int. Conf. On DC. Microgrids (ICDCM), June-2017

76. Selection process
Proposed methodology
76
FB
SAB
LLCSRC
SRC#
0
1
Availability
Losses
Ratings
Repair costs
Power density
11
1 1
Worse
Better
Concept selection
with Pugh matrix
Enter current baseline
design
FULL Bridge converter
List optional concepts:
SAB
LLC
SRC
SRC#
List key design criterion
Availability
Losses
Ratings/Cost
Repair costs
Power density
Determine criterion
weight
Availability - 5
Losses - 4
Ratings/Cost - 3
Repair costs - 2
Power density - 1
Sum the scores for each
concept
Select best concept
”Selection of DC/DC converter for offshore wind farm with MVDC power collection”, C. Dincan, P.C.Kjær, Y. Chen, S.M. Nielsen, C.L. Bak, Proc. IEEE Eur. Conf.
Pow. Electron. And Appl. (EPE2017)
www.dcc.et.aau.dk