Servosila-Device-Reference-0xA020192

not immediately obvious why it is so, but just know that it is so due to some
laws of physics: input voltage limits maximum reachable speed.
The permanent magnets of the rotor come with a magnetic field attached to
them, the one that interacts with coils and produces the Back-Emf voltage
(as well as torque). What "Field Weakening" technique does is that it drives
an additional electric current through the stator coils in such a way that it
creates a magnetic field in the coils that cancels out some of the magnetic
field attached to the permanent magnets of the rotor. In other words, the
coils are used as electromagnets to cancel out a portion of the permanent
magnets' field. The net effect is that the permanent magnets become
"weaker". Weaker magnets generate weaker Back-Emf voltage in coils. This
means that higher speeds can be reached before the "weaker" Back-Emf
voltage matches the voltage of a power supply and the motor stops
accelerating.
To summarize, by enabling the Field Weakening feature, the permanent
magnets of the motor are instantly made "weaker" as some of their magnetic
field is canceled out by an opposing magnetic field generated by the coils.
This reduces the torque of the motor, but increases the maximum reachable
speed. This transformation is made instantly by toggling this configuration
parameter, just like shifting a gear in a car.
A drawback of Field Weakening is its energy inefficiency due excessive heat
generated by the coils. What happens is that the additional electric current
driven through the coils to weaken the field of permanent magnets, is not
used for producing useful torque, but instead is heating the motor. This
wastes some of the energy on heating rather than torque.
If higher speeds are needed for a particular application, it is might be a
better design decision to either increase the voltage of power supply, or
swap the motor for one with a lower Back-Emf (Ke) constant. However,
using the "Field Weakening" technique is appropriate for many applications.
4 Feature: D-Q
Coupling
Compensation (Feed-
Forward)
0 or 1 "D-Q Coupling Compensation" is an advanced motor control technique that
facilitates smooth transitions between modes of operation of an electrical
drive.
For example, if an electric drive is running under Electronic Speed Control
(ESC), and then is given a command to switch to Electronics Torque Control
(ETC), such a transition might cause a sudden change in electric currents
flowing through the motor due to a difference in control laws. This change
might cause a ripple in torque, mechanically stress the drive, or produce an
audible jolt. The "D-Q Coupling Compensation" feature, when enabled,
facilitates a smooth transition between various modes of operation.
The reason the feature is not enabled by default is because the feature
requires that the speed of the motor is correctly measured by the controller.
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