User Manual

Table Of Contents
Field Oriented Control (FOC) mode Operation
Advanced Digital Motor Controller User Manual 139
The challenge in induction motors is that the rotor flux’s absolute position cannot be mea-
sured physically. It is determined mathematically using known speed, voltage and current,
and a model representation of the motors main parameters shown in the figure below.
Rs
Stator
Resistance
Lls
Stator
Leakage
Inductance
Rr
Rotor
Resistance
Llr
Rotor
Leakage
Inductance
Lm
Mutual
Inductance
FIGURE 9-7. Electrical representation of ACIM
These parameters include per phase rotor resistance ‘Rr’, rotor leakage inductance ‘Llr,
mutual inductance ‘Lm’ and rotor leakage inductance ‘Llr. Usually, motor manufacturer will
provide you an equivalent circuit of the induction motor that contains Rr, Rs, Lm, Llr, Lls
In FOC, therefore, rotor flux and motor torque can be individually controlled regardless
of load and speed. FOC offers better dynamic performance, accurate current control and
ensures maximum efficiency, unlike traditional scalar control methods such as Open Loop
VpH and Constant Slip Control.
Under FOC operation, AC induction motors can be run in either FOC torque mode or FOC
speed mode. FOC torque mode allows users to command a torque to a motor in terms of
Amps. While FOC speed will regulate the speed at the command/desired value.
Note that, with a bad tuning of FOC (flux and torque) PID, the motor Amps can be higher
than the Amps Limit. If that happened, try use lower bandwidth for FOC tuning (see in
Chapter FOC Gains Determination & Tuning).
Configuring FOC Torque Mode
To configure FOC mode, first set the controller in Open Loop (Volts per Hertz) mode as
described in one of the previous sections. Verify that the motor is spinning in the desired
direction and that encoder is working and is counting with the correct polarity. See Testing
the Encoder section above.
Once the encoder is verified to work and the motor spins in the open loop, follow these
steps. Using the Roborun PC utility:
Enter the motor parameters under the section “Motor Parameters” in RoboRun
configuration. Usually, motor manufacturer will provide you an equivalent circuit of the
induction motor that contains Rr, Rs, Lm, Llr, Lls.
Set the Flux Amps. In order to find the optimal flux amps, run the motor in Volts per
Hertz (VpH) mode with small/no load using the motor’s rated VpH ratio. Then watch the
flux amps in the PC utility. Enter this value in the configuration. This flux amps can be