1. Direct Torque Control of Induction Machine
Dr. Nik Rumzi Nik Idris
Department of Energy Conversion,
Faculty of Electrical Engineering,
Universiti Teknologi Malaysia

2. Basic Principles of DTC
High performance induction motor drives
Field Oriented Control - FOC
Direct Torque Control DTC

3. Basic Principles of DTC
Tref
Voltage vector selector
Voltage Source Inverter
Stator flux and torque
estimator
ref + _ IM   T
+ Vdc Sa Sb Sc
Stator flux and torque control within hysteresis bands
Voltage vector selected based on stator flux and torque demands

4. Basic Principles of DTC
How the voltage vectors control the flux?
How the voltage vectors control the torque?
These questions will be answered in the following slides

5. Basic Principles of DTC
Space vector equations of IM :

6. Basic Principles of DTC
Space vector equations of IM :

7. Basic Principles of DTC
Direct Flux Control
From stator voltage equation :
Neglecting drop across Rs :

8. Basic Principles of DTC
Direct Flux Control
Voltage vectors for 3-phase VSI

9. Basic Principles of DTCDy
Hysteresis Flux band
100
110
010
011
101
001 y s
Direct Flux Control

10. Basic Principles of DTC
Direct Flux Control q
Sector IV
Sector III
60o I d
Sector II
Sector V
Sector VI
Sector I

11. Basic Principles of DTC
Direct Flux Control
vs,3
vs,2
vs,4
Sector I
Sector II
Hysteresis
band
vs,6
vs,5
vs,16
If the flux in kth sector
k +1 vector increases 
k + 2 vector reduces 
Voltage vector vs,2 and vs,3 in sector I
Voltage vector vs,3 and vs,4 in sector II

12. Basic Principles of DTC
Direct Flux Control
ref + /2
ref - /2
/2
- /2
Flux error
Flux
Error Status 1 t
ref 
ref + _ 1 
Flux error status
Flux
error

13. Basic Principles of DTC
Direct Torque Control
IM torque equation

14. Basic Principles of DTC
Direct Torque Control
It can be shown that
Rotor flux follows the stator flux with a time constant r

15. Basic Principles of DTC
Direct Torque Control
t = t1 q q
t = t1 + t
Applying voltage vectors rotating in the same direction s s
Rotate
continuously
Rotate
continuously
sr
sr r d r d q
t = t1 + t
Applying voltage vectors in opposite direction or zero voltage vectors s
Rotate
continuously
sr r d

16. Basic Principles of DTC
Direct Torque Control
Three cases are considered :
Case 1
Forward active voltage vectors
stator flux increases or decreases
Increases sr
Increases Torque

17. Basic Principles of DTC
Direct Torque Control
Case 2
Zero voltage vectors
stator flux stops
Decreases sr
Decreases Torque

18. Basic Principles of DTC
Direct Torque Control
Case 3
Reverse active voltage vectors
stator flux increases or decreases
Decreases sr rapidly
Decreases Torque rapidly

19. Basic Principles of DTC
Direct Torque Control
Torque
reference
Torque
T/2
T/2 -1 T
Tref + _ 1 T
Torque error T
Speed 1
Torque error status -1

20. Basic Principles of DTC
By limiting the torque and flux within their hysteresis bands, de-coupling of torque and flux can be achieved

21. Basic Principles of DTC
Tref
Voltage vector selector
Voltage Source Inverter
Stator flux and torque
estimator
ref + _ IM   T
+ Vdc Sa Sb Sc
Stator flux and torque control within hysteresis bands
Voltage vector selected based on stator flux and torque demands

22. Basic Principles of DTC
Selection table for optimum switching pattern

23. Stator Flux and Torque Estimation
Accurate estimation to ensure proper operation and stability
Various methods proposed
voltage model
current model
closed-loop observer

24. Stator Flux and Torque Estimation
Stator flux- voltage model
Problems:
dc drift
stator resistance variation

25. Stator Flux and Torque Estimation
In d-q form

26. Implementation of DTC Basic I/O requirements:
Phase Current measurement
DC Link Voltage measurement
Speed measurement from Incremental Encoder for closed-loop speed control (optional)
Fast processor to reduce torque ripple

27. Implementation of DTC

28. Experimental Results From oscilloscope 55s sampling, 240V, ¼ HP IM
Step speed reference
Speed
Current
Torque
d-flux

29. Experimental Results From oscilloscope 55s sampling, 240V, ¼ HP IM
Square wave speed reference
Speed
Current
Torque