TMC4671 Datasheet • IC Version V1.00 | Document Revision V1.04 • 2018-Dec-11
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block and separate controller box wired with motor cable and encoder cable. The high integration of FOC,
together with velocity controller and position controller as a SoC, enables the FOC as a standard peripheral
component that transforms digital information into physical motion. Compact size together with high
performance and energy efficiency especially for battery powered mobile systems are enabling factors
when embedded goes autonomous.
3.4 How does FOC work?
Two force components act on the rotor of an electric motor. One component is just pulling in radial
direction (ID) where the other component is applying torque by pulling tangentially (IQ). The ideal FOC
performs a closed loop current control that results in a pure torque generating current IQ – without direct
current ID.
Figure 2: FOC optimizes torque by closed loop control while maximizing IQ and minimizing ID to 0
From top point of view, the FOC for 3-phase motors uses three phase currents of the stator interpreted as
a current vector (Iu; Iv; Iw) and calculates three voltages interpreted as a voltage vector (Uu; Uv; Uw) taking
the orientation of the rotor into account in a way that only a torque generating current IQ results.
From top point of view, the FOC for 2-phase motors uses two phase currents of the stator interpreted
as a current vector (Ix; Iy) and calculates two voltages interpreted as a voltage vector (Ux; Uy) taking the
orientation of the rotor into account in a way that only a torque generating current IQ results.
To do so, the knowledge of some static parameters (number of pole pairs of the motor, number of pulses
per revolution of an used encoder, orientation of encoder relative to magnetic axis of the rotor, count
direction of the encoder) is required together with some dynamic parameters (phase currents, orientation
of the rotor).
The adjustment of P parameter P and I parameters of two PI controllers for closed loop control of the
phase currents depends on electrical parameters of the motor (resistance, inductance, back EMF constant
of the motor that is also the torque constant of the motor, supply voltage).
3.5 What is Required for FOC?
The FOC needs to know the direction of the magnetic axis of the rotor of the motor in refrence to
the magnetic axis of the stator of the motor. The magnetic flux of the stator is calculated from the
currents through the phases of the motor. The magnetic flux of the rotor is fixed to the rotor and thereby
determined by an encoder device.
For the FOC, the user needs to measure the currents through the coils of the stator and the angle of the
rotor. The measured angle of the rotor needs to be adjusted to the magnetic axes.
The challenge of the FOC is the high number of degrees of freedom in all parameters.
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