DIRECT DRIVE WIND-TURBINE PAPER

1. DIRECT DRIVE WIND TURBINE
Mr.Shivanand.V.Angadi
Jagadguru Tontadarya College Of Arts,
Science And Commerce Gadag- Betageri
shivanand1964@gmail.com
ABSTRACT
Main reason for the adoption of wind energy system. Classification of wind turbines
based their structure, speed and motors used in the WPP’s. The detailed theory of direct
drive wind turbine including their configuration, working principle and modelling. The
comparative results of direct drive WT’s in terms of merits and demerits are discussed.
Keywords:
wind turbine direct drive turbines, variable speed constant speed, induction generator, double fed
induction generator.
1. INTRODUCTION
Electric power is the necessity of human life now a day. since many decades’ people relay
on fossil fuels such as petrol, diesel, coal etc for the generation of electric power. From
the beginning of 20th
century people start of thinking alternative resources of energies,
they found nonconventional energy sources like solar energy, wind energy, biomass,
geothermal etc. The wind energy is ultimately a promising one among the listed resources,
because the wind potential abundance, abundance of suitable landscapes, vital
technological developments in wind turbines and less possible impacts on human life.
In this presentation, direct drive wind turbine is discussed. The wind turbines are
classified into different types such as type-A, type-B, type-C and type-D. Again they are
classified as fixed speed and variable speed types. They further subdivided into SCIG,
WRIG, DFIG and PMSG types. Here both type of direct drive wind turbine is discussed.
2. RESULT :
Conclusion: The comparative study reviewed that the variable speed operation of WPPs, not only
the electrical power extraction is enhanced but also the stresses on the mechanical structure are reduced. The
energy from the wind gusts is partially transferred into the acceleration of the wind turbine rotor and therefore,

2. there is no need to reduce the blade pitch angle instantaneously. Moreover, there is a greater control of active
and reactive power and lesser acoustic noise.
DIRECT DRIVE WINDTURBINE
INTRODUCTION:
This topology was the first in Type-D WPP with variable speed WRSG category and
pioneered by Enercon who harnessed the widely variable wind speeds (see Figure 1) in
early 1990s. The WRSG in this WPP has a separately excited salient pole rotor directly
connected to the wind turbine rotor hub by a slow moving shaft. The large multipole
stator in the shape of a ring is fastened onto the yoke ring whereby the WRSG is also
called as ring generator (or annular generator).
Working Principle
In this topology, the RPM of a multipole generator is same as the wind turbine rotor. The
basic characteristic of the WRSG is that its rotor speed is always locked and in
synchronism with the stator rotating magnetic field. With varying wind speeds, the
voltage and frequency at the generator terminals are also not constant and they vary. As
these do not match with that of the grid voltage and frequency, the WRSG is fully
decoupled by the fully rated PEC and the varying electric power from the stator is
connected to the electric grid after being treated in the four-quadrant operating PEC, as
discussed in earlier sections.
Voltage control is affected by controlling the magnetizing level of WRSG, i.e., high
magnetizing level results in high voltage and production of reactive power. In other
words, it can be said that an ideal WPP has the ability to export and import net reactive
power at full load over a range of grid voltages.
The electronic controller of the direct-drive WPP continuously monitors the grid
parameters and if the grid power factor becomes low, without use of any capacitors, the
PEC will automatically feed reactive power to the grid to improve the power factor.

3. Figure 1 Type-D Direct Drive WPP with Variable Speed WRSG: The generator
rotor has field coils that are separately excited, by a separate DC supply through
slip rings and brushes. The full power from stator is fed to the full rated PEC.
Direct-drive WPPs can continue to operate at lower power capacities (see Figure 2) if
the grids do not have temporary or long term overcapacities. Setting a power gradient in
direct-drive WPPs (a salient feature of this type of WPP) helps in adjusting the power
gradient regulation (see Figure 3) and in optimally suppressing the flicker and voltage
fluctuations even in very weak grids.
Figure 2 WRSG Power Regulation: Possible direct-drive WPP operation when grids do not
have temporary or long term overcapacities.

4. Figure3 WRSG Power Gradient Regulation dpldt. Possible in direct- drive WPPs to
minimize the flicker and voltage fluctuations.
With recent developments, fault-ride-through capability (that means it remains connected
to the grid even during grid faults) to a limited extent is provided with WRSGs, a feature
which is very much required by the grid operators. Power ramp regulation is also being
provided with WRSGs. However, owing to the presence of PECs in the stator connections to
the grid, this type of generator cannot contribute much to system inertia.
DIRECT-DRIVE WPP WITH VARIABLE SPEED PMSG
One of the main drawbacks of Type-D direct-drive WPP with WRSG is the high
maintenance of slip rings and brushes. This problem is solved by low speed direct-drive
WPP with PMSG (see Figure 4), Its inherent self-excitation characteristic lowers the
maintenance problem to a great extent. Since the modern rare earth.
Figure 4 Type-D Direct-drive WPP with PMSG: Since the generator rotor has permanent magnets, it is self-excited and therefore,
does not require separate field coils and separate DC supply to excite them, thereby eliminating the need for slip rings and brushes.
permanent magnets have the ability to produce large quantities of magnetic flux within a very

5. small volume and geometry, they permit high pole count designs and complement the low speed direct-drive
WPP application. For the same rating, a PMSG has a relatively smaller volume than a WRSG due to the
absence of windings in the generator rotor, leading to slightly lower weight which results in a lower THM.
Working Principle
This PMSG topology is more competitive because it can have higher pole count of 60 or more
poles as compared to a conventional WRSG. The permanent magnet rotor of the radial flux PMSG is directly
connected to the varying speed, WPP rotor (between 7 RPM-20 RPM, depending on the rotor diameter size).
Larger the diameter, the slower will be the speed of rotation. Direct-drive WPP with PMSG can have
following two different constructions:
• Outer stator coils and inner rotor mounted with permanent magnets (see Figure 4 ).
• Inner stator coils and outer rotor mounted with permanent magnets (see Figure 5).
Figure 6 Type-D Direct-driveWPP with Inner PMSG Rotor: Nacelle length is shorter due to
absence of gearbox in direct-drive WPPs and the multipole generator rotates at the same
slow speed as the rotors.
Figure 6 depicts the typical external stator coils and internal permanent magnet rotor
constructional design of 1.5 MW Leitwind Type-D direct-drive WPP with PMSG.
Whereas, Figure 3.20A, depicts the typical outer rotor and inner stator constructional design

6. of 1.5 MW Vensys design (licensed to Regen Power-tech, India' type-D direct-drive WPP with
PMSG.
Figure 7 Type-D Direct Drive WPP with Outer PMSG Rotor: The radial flux strategy forms the externally
rotating rotor frame of this PMSG. This helps to increase the torque due to the increase in
bore diameter.
Irrespective of the type of permanent magnet rotor construction (inner or outer), the stator of the
radial flux PMSG has a three-phase symmetrically distributed Stator winding wound around a large number of poles
(multipole) to adjust the speed of slow moving rotor. During normal operation of the WPP, the rotor speed the PMSG is
always locked to the stator exactly proportional to the frequency of the electrical grid. Changes in load cause the
PMSG rotor to advance or drop back a few degrees (called the load angle δ) from the rotating magnetic field of me
stator supplied by the grid. If the torques or currents necessary to accomplish this speed exceed the rated PMSG rating, then
the circuit breakers will open,
there by disconnecting it from the grid in order to protect the generator from getting damaged.
There is no significant starting current when the PMSG is supplied by a PEC and the relation between
the starting and the nominal currents is very low. This is one of the greatest asset of the PMSG that the o utput power is
sinusoidal which is the requirement of a grid operator. There is no exchange of reactive power between the PMSG and GSC
during normal operation; ii only absorbs electric power.
The control of reactive power and the voltage in the WPP equipped with PMSG is defined
by the control system of GSC. Transfer of electric power is through the IC link bus of the PEC. However, the permanent
magnet excitation cannot be controlled as in WRSG electromagnets and so, the output voltage falls, as load is increased.
Therefore, a voltage regulator is needed in most applications. However, the PEC between PMSG stator and grid solves this
problem to a certain extent. In the case of a WRSG, the reactive power is not a problem, since it is produced
internally using the electromagnetic field winding.
One issue for the PMSG regarding the PECs in the stator connections to the grid is that it
cannot contribute much to the system inertia. Another issue is cogging. It is an inherent
characteristic peculiar to slotted PMSGs which is not much of an issue in WRSG, and hence,

7. needs to be taken care during design. Modern WPPs with PMSG fault-ride-through capability
(to remain connected to the grid during system faults), exists to a limited extent, subject to
their rating.
Therefore, PMSG solution yields a higher efficiency throughout the whole variable speed
operation range that results in smaller power fluctuations and lower rotor noise even during
partial power operation.
SALIENT FEATURES OF TYPE-D DIRECT-DRIVE WPP
Following are some of the positive features of type-D direct-drive WPP with synchronous
generator:
i. Absence of gearbox maintenance and failures.
ii. The rotor blades and the large size generator have considerable inertia that functions as a
flywheel (absorbing and storing the energy temporarily as a buffer) smoothing out the aerodynamic torque
fluctuations that results in less mechanical stress on the drive train, especially during the blade passing frequency.
iii. There is a reduced loading on mechanical components. Lesser fatigue loads on blades,
tower and different parts of the WPP, as wind gusts can be absorbed by the inertia of
the WPP creating an elasticity which reduces torque pulsations that results in lesser
electric power fluctuations as well.
iv. These WPPs have lesser number of bearings and couplings.
v. Net energy capture at partial load (which is quite common, as the wind does not
always blow at rated speed conditions for full load operations) is maximized by optimal
TSR operation by Type-D WPPs, thereby maximizing the aerodynamic efficiency of the WPP rotor.
vi. The pitch control can be simpler because the time constant can be longer for variable
speed operations.
vii. These WPPs can easily comply with the requirements of grid operators, as the active
and reactive power can be controlled and large wind farms can even act as a source of
reactive power to compensate poor power factor of other consumers on the electrical
network particularly in remote locations and offshore WPPs.
viii. These slow rotating WPPs produce lesser tip noise at low wind speeds.
ix. Due to the full rated PEC (in contrast to one-third rated PEC of type-C WPP), it can
deliver more reactive power (100%) to support a stable voltage level.
x. Voltage flicker problems are reduced.
xi. Although the electrical efficiency decreases due to the losses in the PECs that are

8. essential for Type-D WPPs, the increase in rotor efficiency outweighs the losses of
the PEC.
xii. Fault-ride-through (FRT) is possible.
LIMITATIONS TYPE-D DIRECT-DRIVE WPPS
i. Type-D WPPs can only be connected to the grid when frequency, phase position and
voltage of the power produced are in synchronism with the grid.
ii. Absence of gearbox is offset by a larger PEC (requiring greater cooling arrangements)
with more complicated circuits for which expert maintenance personnel is difficult to
get on time, as many of the wind farms are in remote and rural locations.
iii. Type-D WPPs due to commutation losses, continuously lose 1% to 2% of the nominal
power in generating and maintaining the magnetic field. Additional maintenance and
heat dissipation is required.
iv. The PECs are sensitive to voltage dips caused by faults and/or switching. IGBT
switches in the PECs are very sensitive to thermal overloads, over currents and over
voltages. In such cases, to prevent their damage, the PEC may block, i.e., stop
switching. Converter blocking may lead to disconnection of the WPPs which is not
acceptable to most of the TSOs.
v. As the power of the WPPs increase in the megawatt range, direct-drr. - WPPs become
heavier and more expensive generator. Their top head mair is relatively much more
than that of geared WPPs.
vi. As compared to a SCIG of similar size, the WRSG is mechanically at: electrically more
complicated.
There is a substantial cost difference between the constant speed WPPs an: variable speed
WPPs. If proper cable shielding is not done, the electrical noise can create problem; for control
signals within the WPP. With the use of optical fiber cables, this problem is being minimized.
3. CONCLUSIONS
The comparative study reviewed that the variable speed operation of WPPs, not only the
electrical power extraction is enhanced but also the stresses on the mechanical structure are reduced. The
energy from the wind gusts is partially transferred into the acceleration of the wind turbine rotor and therefore,
there is no need to reduce the blade pitch angle instantaneously. Moreover, there is a greater control of active
and reactive power and lesser acoustic noise.
Acknowledgement

9. This work was supported and funded by UGC as the part of minor research project under UGC XIIth
plan.
Biography (Times New Roman 10) (alternatively)
Text (Times New Roman 10)
References (Times New Roman 12)
[1] T. Borowski, World Scientific News 7 (2015) 20-52.
[2] Z. S. Hamidi, N. N. M. Shariff, C. Monstein, World Scientific News 52 (2016) 70-80.
[3] Dinendra Raychaudhuri, Sumana Saha, Souvik Sen, Dhruba Chandra Dhali, World
Scientific News 20 (2015) 1-339
[4] G. Thirunarayanan, World Scientific News 53(3) (2016) 138-156.
[5] C.G. Swain, E.C. Lupton Jr., Journal of the American Chemical Society 90 (1968)
4328-4337.
[6] W. F. Winecoff and D.W. Boykin Jr., J. Org. Chem. 37(4) (1972) 674-676.
[7] B. O. Johnson, Journal of Environmental and Biological Science 12(4) (2010) 48-59.
[8] L. F. Crofton, B. J. Horne & G. O. Miller, American Journal of Respiratory Diseases
10(11) (2013) 456-467.
[9] G. Fatima, M. Ahamed, W. Rehman, International Journal of Business and Social
Sciences 3(7) (2012) 203-208.
[10] A. Patwardhan & R. P. Athalye, Genus 21(4) (2010) 505-511.
[11] P. H. Wimberger, Biol. J. Linn. Soc. 45 (1992) 197-218.
[12] Jack L. Jenkins, The English Journal 55(9) (1966) 1180-1182.
[13] M. Ferber, English Literary Renaissance 20(3) (1990) 431-464.
[14] etc. ….

10. This work was supported and funded by UGC as the part of minor research project under UGC XIIth
plan.
Biography (Times New Roman 10) (alternatively)
Text (Times New Roman 10)
References (Times New Roman 12)
[1] T. Borowski, World Scientific News 7 (2015) 20-52.
[2] Z. S. Hamidi, N. N. M. Shariff, C. Monstein, World Scientific News 52 (2016) 70-80.
[3] Dinendra Raychaudhuri, Sumana Saha, Souvik Sen, Dhruba Chandra Dhali, World
Scientific News 20 (2015) 1-339
[4] G. Thirunarayanan, World Scientific News 53(3) (2016) 138-156.
[5] C.G. Swain, E.C. Lupton Jr., Journal of the American Chemical Society 90 (1968)
4328-4337.
[6] W. F. Winecoff and D.W. Boykin Jr., J. Org. Chem. 37(4) (1972) 674-676.
[7] B. O. Johnson, Journal of Environmental and Biological Science 12(4) (2010) 48-59.
[8] L. F. Crofton, B. J. Horne & G. O. Miller, American Journal of Respiratory Diseases
10(11) (2013) 456-467.
[9] G. Fatima, M. Ahamed, W. Rehman, International Journal of Business and Social
Sciences 3(7) (2012) 203-208.
[10] A. Patwardhan & R. P. Athalye, Genus 21(4) (2010) 505-511.
[11] P. H. Wimberger, Biol. J. Linn. Soc. 45 (1992) 197-218.
[12] Jack L. Jenkins, The English Journal 55(9) (1966) 1180-1182.
[13] M. Ferber, English Literary Renaissance 20(3) (1990) 431-464.
[14] etc. ….