This document proposes a direct torque control strategy for doubly fed induction machine-based wind turbines that can operate under voltage dips without crowbar protection. The control strategy generates a rotor flux amplitude reference to control the torque of the wind turbine and reduce stator and rotor overcurrents during faults. It also provides fast dynamic response. While the control does not eliminate the need for crowbar protection entirely, it can prevent the crowbar from activating during low-depth voltage dips. The direct torque control approach maintains machine connection to the grid and reduces torque oscillations during faults.

1. Direct Torque Control for Doubly Fed Induction
Machine-Based Wind Turbines
Under Voltage Dips and Without Crowbar
Protection

2. Abstract:-
This paper proposes a rotor flux amplitude reference generation
strategy for doubly fed induction machine based wind turbines.
It is specially designed to address perturbations, such as voltage
dips, keeping controlled the torque of the wind turbine, and
considerably reducing the stator and rotor over currents during faults.
In addition, a direct torque control strategy that provides fast
dynamic response accompanies the overall control of the wind turbine.
Despite the fact that the proposed control does not totally
eliminate the necessity of the typical crowbar protection for this kind of
turbines, it eliminates the activation of this protection during low depth
voltage dips.

3. Aim:-
 The main aim of the project is to analyze the performance of the
double fed induction generator(DFIG) which is an integral part of the
wind energy generation system under unbalanced grid fault condition. .
And we have to control the speed of the induction generator to
produce constant current even in voltage dips and un balanced load
conditions by using a new method Direct torque control method
with out using crowbar protections.

4. INTRODUCTION
 Here we discuss about the analysis on the control of doubly fed
induction machine (DFIM) based high-power wind turbines when they
operate under presence of voltage dips.
 Most of the wind turbine manufacturers build this kind of wind turbines
with a back-to-back converter sized to approximately 30% of the
nominal power.
 This reduced converter design provokes that when the machine is
affected by voltage dips, it needs a special crowbar protection in order
to avoid damages in the wind turbine and meet the grid-code
requirements.

5.  The main objective of the control strategy proposed in this project is to
eliminate the necessity of the crowbar protection when low-depth
voltage dips occurs.
 Hence, by using direct torque control (DTC), with a proper rotor flux
generation strategy, during the fault it will be possible to maintain the
machine connected to the grid, generating power from the
wind, reducing over currents, and eliminating the torque oscillations
that normally produce such voltage dips

6. Conventional Methods:-
Sensor methods
Power electronic converters (VSI)
Sensor less methods (Adaptive observer method)
Crowbar protection

7. Disadvantages:-
• Increases the size of the machine
• Noise pollution
• Drift effects are increased
– By using A.O techniques
• Require more memory space,
• Have to check for number of estimated values,
• Difficult to tune with number of values,
• More complex of calculating part.

8. Proposed method:-
• Direct torque control method is one of the best control strategies which
allow a torque control in steady state and transient operation of
induction motor.
• The main aim of direct torque control strategies is to effectively control
the torque and flux of induction motor.
• Direct torque control method made the motor more accurate and fast
torque control, high dynamic speed response and simple to control.

10. Advantages:-
– No need to use sensors.
– Efficient output.
– No chance of drift effects and power losses.
– No need to use a crowbar protection.
– Reduce the stator and rotor over currents during faults.

11. Wind Generation
• When wind strikes the stationary blade of the
wind turbine forcely then it starts rotating.

12.  This blades are connected to hub it is
connected to low speed shaft.

13.  This shaft starts rotate with the speed of wind and give
dynamic energy to Gear box.
 This gear box connected to Generator with high speed level
shaft to give more dynamic energy to the Generator
 This Generator converts this Gearbox M.E into E.E.
 This is the general process to generate electricity through
Wind energy.

14. Why we use DFIG?
• Generally in wind generation we use DFIG.
• The reason is the speed of the rotor is based upon the wind speed.
• Wind speed is varies at every time. Due to this variation of speed the
rotor shaft will be damaged.
• To overcome this problem in wind generation we use a specially
designed machine “Double fed induction generator”
• It can withstand under presence of voltage dips,
• Ability to control rotor currents.
• Allows for reactive power control and variable speed operation.

15. Methods of Speed Control of Induction motors
(1) Stator voltage Control
(2) Stator Frequency Control
(3) Stator Current Control
(4) V/F Control
(5) Slip power recovery Control ( Wound Rotor Induction Machine)
15

16. • General control techniques to control the speed of the Induction
Motor are
– Stator side
– Rotor side

18. • But it is difficult to control through Rotor side and Stator side.
The next step is to control the I.M is by using Sensors.

19. Disadvantages of sensors:-
If we use sensors to control IM,
I. We have to put voltage and current sensors at both stator and rotor
sides.
II. So It increases the size of the machine and
III. It increases the cost of the machine.
IV. If we use sensors in get some noisy, and sound polluted.
V. Drift effects are increased.
To over come this problems the next step to control the I.M we go for
sensor less techniques.

21. By using this AO Techniques we get accuracy output, but the
main disadvantages are
a) Require more memory space,
b) Have to check for number of estimated values,
c) Difficult to tune with number of values,
d) More complex of calculating part.
To overcome this problems we use Crow-Bar protection.

22. Crowbar protection.
• It is used to mitigate the high voltages and high current
ratings.
• A crowbar thyristor is connected across the input dc
terminals.
• A current sensing resistor detects the value of converter
current. If it exceeds preset value, gate circuit provides the
signal to crowbar SCR and turns it on in a few microseconds.

24. • If we use Crow-Bar protection if any fault occurs
– we have to replace the fuse and Thyristor.
– The circuit became complex to design
– The size and cost of the equipment increased.
– Externally we have to add another device to reduce voltage
dips.
In order to overcome these problems and to reduce the faults
with in the transmission here we use a new method
Direct Torque Control Method.

25. Principles of Vector Control
The basic conceptual implementation of vector control is
illustrated in the below block diagram:
Note: The inverter is omitted from this diagram.

26. The motor phase currents, ia, ib and ic are converted to idss and
iqss in the stationary reference frame. These are then
converted to the synchronously rotating reference frame d-q
currents, ids and iqs.
In the controller two inverse transforms are performed:
1) From the synchronous d-q to the
stationary d-q reference frame;
2) From d*-q* to a*, b*, c*.

27. There are two approaches to vector control:
1) Direct field oriented current control
- here the rotation angle of the iqse vector with respect to the
stator flux s
qr ’ is being directly determined (e.g. by measuring
air gap flux)
2) Indirect field oriented current control
- here the rotor angle is being measured indirectly, such as by
measuring slip speed.

28. Direct Vector Control
In direct vector control the field angle is calculated by using
terminal voltages and current or Hall sensors or flux sense
windings.
A block diagram of a direct vector control method using a PWM
voltage-fed inverter is shown on the next slide.

29. Direct Vector Control (cont’d)

30. The principal vector control parameters, ids* and iqs*, which
are dc values in the synchronously rotating reference frame, are
converted to the stationary reference frame (using the vector
rotation (VR) block) by using the unit vector cos e and sin e.
These stationary reference frame control parameters idss* and
iqss* are then changed to the phase current command
signals, ia*, ib*, and ic* which are fed to the PWM inverter.

31. A flux control loop is used to precisely control the flux. Torque
control is achieved through the current iqs* which is generated
from the speed control loop (which includes a bipolar limiter
that is not shown). The torque can be negative which will
result in a negative phase orientation for iqs in the phasor
diagram.
How do we maintain idsand iqs orthogonality? This is explained
in the next slide.

32. Why FOC ?
• IM is superior to DC machine with respect to
size, weight, inertia, cost, speed
• DC motor is superior to IM with respect to ease of control
– High performance with simple control due de-coupling
component of torque and flux
• FOC transforms the dynamics of IM to become similar to the
DC motor’s – decoupling the torque and flux components

33. Basic Principles DC machine
By keeping flux
constant, torque can be
controlled by controlling
armature current
a
Te = k If Ia
Current in
Current out
f

34. Basic Principles of IM
s
a
Stator current produce stator
r flux
c’ b’
Stator flux induces rotor
current produces rotor flux
Interaction between stator and
rotor fluxes produces torque
b
c
Space angle between stator
and rotor fluxes varies with
load, and speed

35. FOC of IM drive
Torque equation :
3 p
Te s
is
2 2
3 p Lm
Te r is
2 2 Lr
In d-q axis :
3 p Lm
Te ( rd
i sq rq
i sd )
2 2 Lr

36. FOC of IM drive
In d-q axis :
3 p Lm
Te ( rd
i sq rq
i sd )
2 2 Lr
Choose a frame such that:
r
rd r rq
r
0

37. FOC of IM drive
Choose a frame such that:
r
rd r rq
r
0

38. FOC of IM drive
Choose a frame such that:
r
rd r rq
r
0
qs
As seen by stator reference frame:
3 p Lm is
Te ( rd
i sq rq
i sd ) i sq
2 2 Lr
r
rq
i sd ds
rd

39. FOC of IM drive
Choose a frame such that:
r
rd r rq
r
0
qs
Rotating reference frame: r
q
is
d r
3 p Lm
Te ( i ir
r rdsq sq rq
i sd ) r
2 2 Lr r
i sq r
i sd
ds

40. FOC of IM drive
To implement rotor flux FOC need to know rotor flux position:
(i) Indirect FOC
Synchronous speed obtain by adding slip speed and rotor speed
Rotor voltage equation: Rotor flux equation:
g
g d r g
g
L r ir
g
L m is
g
0 R i
r r
j( g r
) r
r
dt
g
Rr g L mR r g d r g
0 r
i s
j( g r
) r
Lr Lr dt
Rr L mR r d r
0 r
i sd
r
ji sq
r
j( slip
) r
Lr Lr dt

41. FOC of IM drive - indirect
d component q component
Rr L mR r d r L mR r
0 r
i sdr 0 i sqr ( slip ) r
Lr Lr dt Lr
Rr L mR r d r
0 r
i sd
r
ji sq
r
j( slip
) r
Lr Lr dt

42. FOC of IM drive - indirect
Rr L mR r d r
0 r
i sd
r
ji sq
r
j( slip
) r
Lr Lr dt
d component q component
*
4 Te Lr
i sqr *
3p r
Lm
Rr L mR r d r L mR r
0 r
i sdr 0 i sqr ( slip ) r
Lr Lr dt Lr
* L mR r
r ( ) i sqr
i sd * r slip *
r
Lr
Lm

43. FOC of IM drive - indirect
T* *
r
i r *
sq isq* ia*
i sdr *
Lm
4 Te
*
Lr 2/3 ib* CC
i sqr *
i r * ej
3p r
Lm sd isd* ic* VSI
*
L mR r
( slip
) *
i sqr
r
Lr
1/s
slip r
+ +
Rotating frame Stationary frame

44. FOC of IM drive
(ii) Direct FOC
Rotor flux estimated from motor’s terminal variables
Rotor flux can be estimated by:
Rr LmR r d r g
0 r
is j r r
Lr Lr dt
Express in stationary frame
3 p Lm
Te r
is
2 2 Lr

45. FOC of IM drive
(ii) Direct FOC
Rr L mR r d r g
0 r
is j r r
Lr Lr dt
Rr L mR r d( rd
j rq
)
0 ( rd
j rq
) ( i sd ji sq )i j r
( rd
j rq
)
Lr Lr dt
d q
Rr L mR r Rr L mR r
i sd dt rq rq
i sq r rd
dt
rd
Lr
rd
Lr
r rq
Lr Lr
rq
2 2
r rd rq
rd

46. FOC of IM drive - direct
T* i r *
sq isq* ia*
TC
2/3 ib* CC
ej
r* isd* VSI
i r *
FC
sd
ic*
r
Te
Rr LmR r d r g
0 r
is j r r
Lr Lr dt
3 p Lm
Te r
is
2 2 Lr
Rotating frame Stationary frame

48. Working:-
 Stator is directly connected Grid
 Rotor is connected supply through Back-Back converters
 We control the speed of the I.M by changing the firing angles at
different level by taking the reference of Direct torque.
 DTC that controls the machine’s torque (Tem ) and the rotor flux
amplitude (|ψr |) with high dynamic capacity, and a second block
that generates the rotor flux amplitude reference, in order to
handle with the voltage dips.

49. What is MATLAB?
MATLAB (Matrix Laboratory)
– MATLAB is developed by The Math Works, Inc.
– MATLAB is a high-level technical computing
language and interactive environment for
algorithm development, data visualization, data
analysis, and numeric computation.
– MATLAB can be install on Unix, Windows

50. • About MATLAB/Simulink:
– Matlab is a high-performance language for technical
computing.
– It integrates computation, visualization, and programming in an
easy-to-use environment where problems and solutions are
expressed in familiar mathematical notation.

51. History of MATLAB:
 Fortran subroutines for solving linear (LINPACK) and eigen value
(EISPACK) problems
 Developed primarily by Cleve Moler in the 1970’s
 Later, when teaching courses in mathematics, Moler wanted his
students to be able to use LINPACK and EISPACK without requiring
knowledge of Fortran
 MATLAB developed as an interactive system to access LINPACK and
EISPACK.
 MATLAB gained popularity primarily through word of mouth because it
was not officially distributed.
 In the 1980’s, MATLAB was rewritten in C with more functionality (such
as plotting routines)

52.  The Mathworks, Inc. was created in 1984
 The Mathworks is now responsible for development, sale, and
support for MATLAB
 The Mathworks is located in Natick,
 The Mathworks is an employer that hires co-ops through our co-op
program

53. Strengths of MATLAB
• MATLAB is relatively easy to learn.
• MATLAB code is optimized to be relatively quick
when performing matrix operations.
• MATLAB may behave like a calculator or as a
programming language.
• MATLAB is interpreted, errors are easier to fix.
• Although primarily procedural, MATLAB does have
some object-oriented elements.

54. Other Features
• 2-D and 3-D graphics functions for visualizing data
• Tools for building custom graphical user interfaces
• Functions for integrating MATLAB based algorithms
with external applications and languages, such as
C, C++, Fortran, Java, COM, and Microsoft Excel

55. Weaknesses of MATLAB
• MATLAB is NOT a general purpose programming
language.
• MATLAB is an interpreted language (making it for
the most part slower than a compiled language
such as C++).
• MATLAB is designed for scientific computation and
is not suitable for some things (such as parsing
text).

56. Components of MATLAB Interface
• Workspace
• Current Directory
• Command History
• Command Window

58. SIMULINK
 It is a commercial tool for modeling, simulating and
analyzing multidomain dynamic systems.
 Its primary interface is a graphical block diagramming
tool and a customizable set of block libraries.
 Simulink is widely used in control theory and digital
signal processing for multidomain simulation
and Model-based design.

59. • Generally there are three ways to open Simulink
1.By using start in Matlab
2.By typing Simulink in Command prompt.
3.By clicking Simulink icon in toolbar.

60. Cont……
Simulink is widely used in control
theory and digital signal processing for
multidomain simulation and Model-based
design.

70. Simulation diagram

71. Simulation results

72. Simulation results

73. • Conclusion:-
we control the speed of the induction generator to produce
constant current even in voltage dips and un balanced load
conditions with out using any crowbar protections and by using
a new method Direct torque control method.