User Manual

Brushless Motor Connections and Operation
118 Advanced Digital Motor Controller User Manual V2.0, July 8, 2019
Field Oriented Control (FOC)
In sinusoidal modes, using the rotor angle to determine the voltage to apply to each of
the 3 motor phase works well at low frequencies, and therefore at low rotation speed. At
higher speed, the effect of the winding inductance, back EMF and other effect from the
motor rotation, create a shifting current. The resulting magnetic field is then no longer op-
timally perpendicular to the rotor’s permanent magnets.
I = Iq
I
Iq
Id
FIGURE 8-15. Perpendicular and non-perpendicular fields
As can be seen in figure 8-10, when the magnetic field is at an angle other than exactly
perpendicular to the rotor’s magnets, the rotor is pulled by a force that can be decom-
posed in two forces:
Lateral force causing torque, and therefore rotation. This force results from the Quadra-
ture current Iq, which is also called Torque current
Parallel force that pulls the rotor outwards, creating no motion. This force results from the
Direct Current Id, which is also called Flux current
Field Oriented Control is a technique that measures the useful Torque current and wasted
Flux current component of the motor current. It then automatically adjust the power and
phase applied to each motor wire in order to eliminate the wasted Flux current
Id
PI Regulator
PI Regulator
Iq
Inverse
Park
SVPWM
Clarke
MOSFET
Bridges
Angle
Capture
Park
i
a
i
b
i
α
i
β
i
q
i
d
i
q
i
d
v
q
v
d
v
α
v
β
-
-
θ
Motor
Sensor
Desired Torque
Current
Desired Flux
Current
FIGURE 8-16. FOC operation