As turbine sizes cross the threshold of 10MW, the wind turbine industry’s key supply chain partners must meet the challenge of developing components that enable turbine OEMs to provide machines that reduce LCoE. Ingeteam’s latest expert report, written in partnership with Windpower Monthly, covers three areas of technological innovation for converters designed specifically for +10MW turbines: - Voltage level - low voltage (LV) to medium voltage (MV) reduces power losses - Number of conversion lines (CL) - Semiconductor chip architectures.

1. THE MERITS AND ADVANTAGES
OF INGETEAM’S THIRD
GENERATION MV CONVERTERS
FOR +10MW TURBINES

2. 2
INTRODUCTION
T
he biggest ongoing challenge facing
the offshore wind industry is driving
down the levelised cost of energy
(LCoE) of wind power.Like onshore wind,
significant reductions in offshore wind
LCoE can be achieved by moving to larger
turbine sizes.
As turbine sizes cross the threshold from
10MW to 12MW,the wind turbine
industry’s key supply chain partners,
including converter manufacturers,must
meet the challenge of developing
components that enable turbine OEMs to
provide machines that reduce LCoE.In
addition,reliability becomes an
increasingly important factor in offshore
wind,as turbines that develop faults or
malfunction can go for longer periods of
downtime,compared with onshore.
It is fair to say that historically,converter
design hasn’t been the major focus of
OEMs,which have tended to target efforts
on turbine designs,including blades,
gearboxes,rotors,nacelle integration,
foundations as part of ongoing efforts to
LCoE.Wherever possible manufacturers
will upgrade existing designs to reduce
risks and this approach to converter
systems is no different.
Ingeteam’s ethos is to be technology
agnostic in developing power converters
for the industry.Our goal is to provide
customers with the solution that works
best for the platforms they are developing.
In many cases DFIG and Full Converter
topologies based on low voltage designs
can meet the key OEM requirements.
However,the next-generation of offshore
wind turbines,with capacities of +10MW,
which will move from prototype stage to
commercial availability in the next four-
to-five years,demand a different approach.
At Ingeteam we have been working closely
* Source: The Global wind
turbine technology market
report by Wood Mackenzie
with the few manufacturers bringing to
market these machines.Our offering is a
third generation medium voltage suite of
converters based on our 15 years of
supplying MV converters for wind,marine
and other industries.
It is expected that by 2022 approximately
30% of the offshore market will be covered
by +10MW turbines and by 2025,the global
market share of these models will be
around 80%*.
In this article Ingeteam covers three key
areas of technological innovation for
converters designed specifically for
+10MW turbines:
n Voltage level – low voltage (LV)
to medium voltage (MV) reduces power
losses
n Number of conversion lines (CL)
n Semiconductor chip architectures
“It is expected
that by 2022
approximately
30% of the
offshore market
will be covered
by +10MW
turbines and by
2025, the global
market share of
these models
will be around
80%”*

3. 3
M
oving to higher voltages,from LV
to MV,reduces losses.As voltage
increases,current levels drop by the
same factor.MV converters for turbines in
the 12MW size range realise current values
of around 3500A,compared with 14kA in
an equivalent LV converter.
Lower nominal currents allow for more
simplified architectures,resulting in
smaller and lighter converters (as pictured
in Table 1 Low voltage FC 2 level topology
power stacks in AFE+INV configuration).
For example,the length of copper bars to
the transformer can be reduced and the
thermal system required to evacuate all
the losses,which would occur in an LV
architecture,are not required.
In addition to voltage level,another
important consideration is the converter
architecture.Neutral point clamped
(NPC) 3L topologies represent the most
extensive MV full converter architecture,
representing an efficiency increase of
1.5%,compared with 2L full converter
architecture,the most widely used
topology for LV converters (see table 2,2L
and 3L topologies).
VOLTAGE LEVEL
FIG 1: LOW VOLTAGE FC 2 LEVEL TOPOLOGY POWER STACKS
IN AFE+INV CONFIGURATION
LV B2B TOPOLOGY UP TO 6MW MV BPM PER PHASE UP TO 5MW
Weight: 300kg Weight= 45kg / Total weight= 270kg

4. 4
A key advantage of the NPC 3L architecture
is that it improves the voltage wave form,
allowing an optimisation – reduction
in size and weight – of the DV/DT filter,
which protects motors against high
voltage increases and voltage peaks,and
the grid filter,due to the reduction of
the power converter’s constant losses
(see Figure 1 Waveform of 2L and NPC 3L
topologies).However,the cost of an NPC
3L topology is higher due to a doubling of
semiconductors at each phase.
Ingeteam’s technology-agnostic approach
is to provide the industry with both LV
and MV solutions,as the market will
demand both types of converters to cover
the range from 8-10MW and from 12-
15MW.For wind turbines around 10MW we
foresee LV Full Converter products could
be the trend of the market.
However,the advantage of going from
LV to MV converters based on NPC 3L
topologies include higher modularity for
offshore turbine designs (+10MW sizes)
with minimized energy loss,as well as
higher efficiency and lower cabling cost.
Such products also provide flexibility
in design options,allowing the power
converted to be installed in the nacelle or
in the tower.Due to their simplified design
MV converters are also easier to maintain,
reducing downtime.
FIG 3: WAVEFORM OF 2L AND 3LNPC TOPOLOGIES
2 LEVELS INVERTER 3 LEVELS INVERTER
FIG 2: 2 LEVEL AND 3 LEVEL TOPOLOGIES
2 LEVEL TOPOLOGIES 3 LEVEL NPC TOPOLOGY

5. 5
These studies consider a standard scenario
with the following characteristics:
n Energy price: 65€/MWh
n Wind class I – offshore wind sites tend
to be this class but though the resources
are better than lower classes low
availability is more highly penalised as
turbines at sea can potentially be down
for longer than those on land.
n MTBF value of a CL: 45000h
n Cases under study: 1-4 CL,covering a
rated power up to 12.5MW
As shown in the chart (see Figure 2
Optimal conversion line selection in terms
of MTTR) the results of Ingeteam’s study
show that the optimal option is to use
2CL lines in parallel,since it covers for a
wide range of MTTR,measured in weeks,
from 1.3 weeks to 3.8 weeks,with lowest
production losses (also see Table 3 Optimal
conversion line selection in terms of
MTTR).
F
or investors in offshore wind reducing
LCoE helps to minimise risk and
maximise return on investment (ROI).
Power converters contribute to the LCoE
metric in two ways: cost and availability.A
lower converter cost in combination with
increased availability results in reduced
LCoE.
Converter availability depends on two
metrics: Mean Time Between Failures
(MTBF) and Mean Time To Repair
(MTTR).Higher MTBF values combined
with lower MTTR values results in
increased availability.There is also a
direct relationship with costs,as higher
investments allow for better materials or
even the addition of redundancies,as well
as optimised maintenance programmes
for example.
Ingeteam has developed several studies in
order to obtain the optimal power range
for the power conversion stage in an
offshore turbine,covering 10-15MW.
CONVERSION LINE SELECTION
TABLE 3: OPTIMAL CONVERSION LINE
SELECTION IN TERMS OF MTTR
12.5MW: 1CL/2CL/3CL/4CL
FIG 2: OPTIMAL CONVERSION
LINE SELECTION IN TERMS
OF MTTR
“A lower
converter cost
in combination
with increased
availability
results in
reduced LCoE” Number of CL Power range -12.5MW
1CL MTTR 1
2CL 1 ≤ MTTR ≤ 4
3CL 4 MTTR ≤ 5
4CL 5 MTTR ≤ 8

6. 6
I
ngeteam offers power converters based
on several chip designs: insulated-gate
bipolar transistor (IGBT),integrated
gate-commutated thyristor (IGCT) and
injection-enhanced gate transistor (IEGT)
semiconductors.
However,for wind turbine as well as
marine and traction applications,the high
voltage (VH) IGBT is considered to be the
best choice due to the following:
n Converter power density has increased
substantially along with semiconductor
evolution
n A robust global supply chain exists for
key components such as IGBTs and
gate drivers with companies such as
Hitachi,Mitsubishi and ABB supplying
semiconductor and gate driver sources
n Roadmaps include further medium
term chip evolutions
n The HV-IGBT is intrinsically proofed
against short-circuiting.In the case of a
short-circuit,the IGBTs can safely turn
off,avoiding any permanent damage.
n The chipset package includes insulation
to the cooling circuit,negating the need
for using deionized water and costs for
heatsinks are reduced
n Reliability and ruggedness of HV-
IGBTs are proven from many years of
operation in harsh environments such
as traction,marine propulsions,and
dredging
n The chipsets entail easy and fast
mounting processes,so there is no need
for tooling for replacement,mounting
and dismounting processes
n Lower maintenance costs
In the past,HV-IGBT semiconductor chips
were not powerful enough for high power
applications in medium voltage,due to
intrinsic characteristics of the IGBT itself.
However,aided by the ongoing evolution
of LV-IGBTs,HV-IGBT performance has
improved thanks to Advanced Trench
Technology (see Figure 3 Chip technology
comparison).
SEMICONDUCTORS
FIG 3: CHIP TECHNOLOGY COMPARISON

7. 7
With this new chip technology,HV-IGBT
losses were reduced and diode current
capability was increased,enabling for
a higher output power capacity from
between 10% and 15%,making the modules
suitable for the most demanding power
applications.
Table 3 shows a comparison between
a Fine Planar technology module and
an Advanced Trench module in an NPC
3L architecture,while Figure 4 shows
switching losses comparisons between
HV-IGBT modules.
FIG 4: SWITCHING LOSSES COMPARISON BETWEEN HV-IGBT MODULES
TABLE 3: CURRENT CAPACITY COMPARISON
BETWEEN HV-IGBT MODULES
VBUS=2800V /
Tj=25ºC /
ISW=2400A Overvoltage - ∆V EON EOFF
MBN1200H45E2-H 3574,7V 6,37J/p 8,19J/p
MBN1500FH45F-H 3946,9V 5,56J/p 7,00J/p
Ratio 1500A/1200A 110% 87% 86%
Figure 5 shows the simplified modules
based on HV-IGBT technology,compared
with those based on IGCT technology.
FIG 5: COMPARISON BETWEEN IGCT IGBT BPMS

8. 8
FIG 6: MODULAR 2 CONVERSION LINE
SYSTEM FOR 10+MW WIND TURBINE
FIG 7: SIMPLIFIED
ELECTRICAL
DIAGRAM OF A 1
POWER CONVERSION
LINE SYSTEM (1PCL)
FOR MV FC
FIG 8: SIMPLIFIED
ELECTRICAL
DIAGRAM OF
A 2 POWER
CONVERSION LINE
SYSTEM (2PCL)
FOR MV FC
T
aking into account voltage,
conversion line and semiconductor
considerations discussed in this
article,Ingeteam proposes an MV full
power NPC 3L converter for turbines of
+10MW (see Figure 6),which has received
DNV GL certification.
The highly modular design aids flexibility,
by allowing the adaptation of each
conversion solution to any type of wind
turbine.It is suitable for OEMs making
machines in smaller sizes as well as the
largest and so could be used with models
ranging from 5MW to 15MW.
The product is designed to work in
different configurations and with
different conversion lines,as figures 7
and 8 illustrate.
SOLUTION OVERVIEW

9. 9
D
ifferent converter technologies are
available for the newest offshore
wind turbines expected to enter
production in the next few years.
However,each wind turbine model
needs to be studied in detail in order
to choose the optimal solution,which
considers the whole picture,including
LCoE,nacelle design,logistics,
reliability and efficiency.
As turbine sizes continue to increase
from 10MW upwards,MV products
provide a range of benefits to OEMs.
These more compact and efficient
systems based on NPC 3L architectures
can be more easily installed within
nacelles,are able to achieve optimized
availability and reduce maintenance,
critical considerations for offshore
wind farms which are more
challenging and costly to service
and maintain than onshore sites.
Based on an installed capacity of more
than 45GW worldwide,Ingeteam is
focused on anticipating the wind
industry’s evolution,while offering
turbine OEMs a full range of options
to meet their individual requirements
when developing new models and
platforms now and in the future.
CONCLUSION

10. For more information on wind power converters and
related products, please contact Ingeteam:
ingeteam.com
Commercial Director - Alberto Barcia
alberto.barcia@ingeteam.com
+34 948 288 000