Vector control allows induction motors to behave like DC motors by controlling the current in the direct and quadrature axes. This provides faster torque response compared to traditional V/Hz control. The basic blocks of a vector controlled drive include calculating the transformation angle, controlling current in the direct and quadrature axes using a current controller, and estimating rotor flux without requiring flux sensors. Speed control of the motor can be achieved using cascade control of the current and speed loops.

1. Vector Control of Induction
Machines
dq
3
2 IM 3
2 dq
s
u s
i
q
q
ab
ab

2. Introduction
• The traditional way to control the speed of
induction motors is the V/Hz-control
• Low dynamic performance
• In applications like servo drives and rolling
mills quick torque response is required.
• Desire to replace dc drives led to vector
control

3. What is vector control?
• Vector control implies that an ac motor is
forced to behave dynamically as a dc
motor by the use of feedback control.
• Always consider the stator frequency to
be a variable quantity.
• Think in synchronous coordinates.

4. Basic blocks of a vector controlled drive
dq
3
2 IM 3
2 dq
s
u s
i
q
q
ab
ab

5. Addition of a block for calculation of
the transformation angle
dq
3
2 IM 3
2 dq
s
u s
i
q
q
ab
ab
Transformation
angle
calculation
r
q

6. The current is controlled in the d- and
q-directions
j
ref ref ref
s sd sq
i i
 
i
magnetization
torque production

7. Vector controller
dq
3
2 IM 3
2 dq
s
u s
i
q
q
ab
ab
Transformation
angle
calculation
r
q
Current
controller
ref
s
i
+
-

8. Rotor flux orientation
• Difficult to find the transformation angle since
the direction of the flux must be known
• Flux measurement is required
• Flux sensors (and fitting) are expensive and
unreliable
• Rotor position measurement does not tell the
flux position
• The solution is flux estimation

9. Rotor flux orientation using measured
flux
Original method suggested by
Blaschke
•Requires flux sensors
•Flux coordinates: aligned with the
rotor flux linkage
arctan r
r
b
a



 
  
 

10. Rotor flux orientation using estimated
flux
• The rotor flux vector cannot be measured,
only the airgap flux.
• Flux sensors reduce the reliability
• Flux sensors increase the cost
• Therefore, it is better to estimate the rotor
flux.

11. The current model
Current
control
Current
model
IM
drive
f
f
s
s
ref
rd

ref
T
f
s
i s
s
i
s
s
u
f
s
u
r
w
̂
̂

12. Speed control
• Applications: pumps and fans in the process
industry, paper and steel mills, robotics and
packaging, electric vehicles
• Very different dynamic requirements
• Most drives have low to medium high
requirements on dynamics. These drives are
considered here.
• Cascade control is sufficient

13. Block diagram of a speed-controlled
drive system
Current
controller ref
u
I

i
ref
i


Speed
controller
Inverter


w

ref
m
w
m
w
Electric
motor

14. Complete system

15. Clarke Transformation

16. Park transformation

17. Space Vector Modulation

18. MATLAB IMPLEMENTATION

19. CURRENT AND SPEED WAVEFORM

20. CURRENT AND SVPWM

21. References
• Zambada, Jorge (Nov 8, 2007). "Field-oriented control for motors". MachineDesign.com.
• Jump up^ Lewin, Chuck (April 10, 2006). "New Developments in Commutation and Motor
Control Techniques". DesignNews.com.
• DSP Manual (2007). "3-Phase AC Induction Vector Control Drive with Single Shunt Current
Sensing" (PDF). Freescale. p. 25, incl. esp. eq. 2–37. Retrieved May 16, 2012.
• Jump up Godbole, Kedar (Sep 23, 2006). "Field oriented control reduces motor size, cost and
power consumption in industrial applications". Texas Instruments.
• Jump up^ Bose, Bimal K. (June 2009). "The Past, Present, and Future of Power
Electronics". Industrial Electronics Magazine, IEEE 3 (2): 11.doi:10.1109/MIE.2009.932709.
• Murray, Aengus (Sep 27, 2007). "Transforming motion: Field-oriented control of ac motors".
EDN. Retrieved 11 May 2012.