Transcript Variable speed direct-drive concept with a full

Overview of different wind
generator systems and their
comparisons 2-4~2-7
陳昱希
Outline
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Variable speed direct-drive concept with a fullscale power converter
Variable speed single-stage geared concept with a
full-scale power converter
Variable speed multiple-stage geared concept with a
full-scale power converter
Variable speed direct-drive concept with
a full-scale power converter
The full-scale power converter can perform
smooth grid connection over the entire speed
range. However, it has a higher cost and a higher
power loss in the power electronics, since all the
generated power has to pass through the power
converter
Types of direct-drive generators used in the
market can be classified into the electrically
excited synchronous generator (EESG) and the
PMSG.
Variable speed direct-drive concept with
a full-scale power converter
Direct-drive types V.S. geared-drive
 Lower generator rotor speed
 Higher torque
 Larger size
 Simplified drive train
 Omitting the gearbox.
 Higher overall efficiency
 High reliability
Electrically excited synchronous
generator (EESG)
The amplitude and frequency of the voltage can
be fully controlled by the power electronic at
the generator side.
 The EESG has the opportunities of controlling
the flux for a minimized loss in different power
ranges, because the excitation current can be
controlled by means of the power converter in
the rotor side.
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PM synchronous generator
The advantages of PM machines over EESG
 Higher efficiency
 No additional power supply for the magnet field
excitation.
Disadvantages
 High cost of PM material
 Difficulties to handle in manufacture
PM synchronous generator
Based on the direction of flux penetration.
 Radial-flux PM machines
 Axial-flux PM machines
 Transversal-flux PM machines
Radial-flux PM machines
The PMs of radial-flux machines are radically
oriented.
 Two types of RFPM machines, the slotted
surface mounted PM machine and the slotted
flux concentrating PM machine
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Axial-flux PM machines
The axial-flux PM (AFPM) machine is a machine
producing magnetic flux in the axial direction.
 The slotless single stator double rotor is a
typical structure of slotless AFPM machines.
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Axial-flux PM machines
AFPM V.S RFPM
Advantages
 Simple winding
 Short axial length
 Higher torque/volume ratio.
Disadvantages
 Lower torque/mass ratio ,
 Difficulty to maintain air gap in large diameter
 Difficulty in production of stator core
Transversal-flux PM machines
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The path of the magnetic flux is perpendicular to
the direction of the rotor rotation.
TFPM machines have some advantages, such as
higher force density, considerably low copper
losses and simple winding.
 TFPM machines have some disadvantages, such
as the electromagnetic structure is much more
complicated ,
low power factor.
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Variable speed single-stage geared
concept with a full-scale power converter
In this scheme, a variable speed pitch control wind
turbine is connected to a single-stage planetary
gearbox that increases the speed by a factor of
roughly10 and a low-speed permanent-magnet
generator.
It has the advantages of a higher speed than the
direct-drive concept and a lower mechanical
component than the multiple-stage gearbox
concept.
Variable speed multiple-stage geared
concept with a full-scale power converter
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A PMSG system with a multiple gearbox is used in
order to reduce the generator’s volume and
improve the generator efficiency in variable speed
wind turbine concepts with a full-scale power
converter.
PMSG system compared with the DFIG
system
Advantages
 The generator has a better efficiency.
 The generator can be brushless.
Disadvantages
 Larger
 More expensive converter
 The losses in the converter are higher
Thanks for your listening