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

2. 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

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

4. Basic Principles of IM s r Stator current produce stator flux
Stator flux induces rotor current  produces rotor flux
Interaction between stator and rotor fluxes produces torque
Space angle between stator and rotor fluxes varies with load, and speed

5. FOC of IM drive
Torque equation :
In d-q axis :

6. FOC of IM drive
In d-q axis :
Choose a frame such that:

7. FOC of IM drive
Choose a frame such that:

8. FOC of IM drive Choose a frame such that: qs
As seen by stator reference frame: ds

9. FOC of IM drive Choose a frame such that: qs Rotating reference frame:
qr
dr ds

10. 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:

11. FOC of IM drive - indirect
d component
q component

12. FOC of IM drive - indirect
d component
q component

13. FOC of IM drive - indirect
ia*
irsq*
isq*
ib* CC
VSI
2/3
ej
irsd*
isd* *
ic*
1/s
slip r + +
Rotating frame
Stationary frame

14. FOC of IM drive (ii) Direct FOC
Rotor flux estimated from motor’s terminal variables
Rotor flux can be estimated by:
Express in stationary frame

15. FOC of IM drive
(ii) Direct FOC d q

16. FOC of IM drive - direct ia* T* isq* TC ib* CC 2/3 ej VSI r* isd*
irsq*
isq* TC
ib* CC
VSI
2/3
ej
r*
irsd*
isd*
ic* FC r Te 
Rotating frame
Stationary frame