Field-Oriented Control of Induction Machine

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Field-Oriented Control of Induction Machine
Dr. Nik Rumzi Nik Idris Department of Energy
Conversion, Faculty of Electrical
Engineering, Universiti Teknologi Malaysia
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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 motors decoupling the torque
  and flux components

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Basic Principles DC machine
By keeping flux constant, torque can be
controlled by controlling armature current
Te k If Ia
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Basic Principles of IM
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
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FOC of IM drive

• Torque equation

In d-q axis
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FOC of IM drive
In d-q axis
Choose a frame such that
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FOC of IM drive
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FOC of IM drive
Choose a frame such that
As seen by stator reference frame
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FOC of IM drive
Choose a frame such that
qs
Rotating reference frame
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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
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FOC of IM drive - indirect
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FOC of IM drive - indirect
q component
d component
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FOC of IM drive - indirect
ia
T
i?rsq
isq
ib
CC VSI
2/3
ej??
i?rsd
isd
ic
?
1/s
?slip
?r


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FOC of IM drive
(ii) Direct FOC
Rotor flux estimated from motors terminal
variables
Rotor flux can be estimated by
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FOC of IM drive
(ii) Direct FOC
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FOC of IM drive - direct
ia
T
isq
i?rsq
TC
ib
CC VSI
2/3
ej??
?r
isd
i?rsd
ic
FC
?r
Te
??