Operation
46
Atlas
®
Digital Amplifier Complete Technical Reference
4
derived from the other two phases. When driving step motors, two current loops are used, one for the phase A coil,
and one for the phase B coil.
There are three overall methods of current control provided by Atlas, however not all methods are used with all motor
types. The first method is individual phase control. See
Section 4.5.2, “Individual Phase Control”
for a description.
Section 4.5.3, “Field Oriented Control”
for a description of the second method, FOC (Field Oriented Control).
Section 4.5.4, “Third Leg Floating Control”
for a description of the third approach, called ‘third leg floating.’ The
table below summarizes which current control modes are available with the three motor types supported by Atlas,
along with the default configuration for that motor type.
The large majority of applications will use FOC to drive Brushless DC or step motors. FOC usually provides the
highest top speeds and more energy efficient operation of the motor compared to individual phase control. Third leg
floating is an option that should generally only be considered for Hall-commutated motors. In that configuration, third
leg floating can sometimes provide a higher top speed than FOC. Finally, individual phase control is always used with
DC Brush motors, and may, under certain specialized conditions, provide improved performance for Brushless DC
motors over FOC.
To select which type of control method will be used, use the command
SetCurrentControlMode
. To read the value
set using this command, use
GetCurrentControlMode
.
4.5.1
Enabling and Disabling the Current Loop
If during normal operation the current loop is disabled, then the output from the commutation module will pass
directly to the power stage module, with no current control being performed. The most common use of this is to run
the amplifier in voltage mode, which may be useful under some conditions for calibration or testing.
To disable the motor output module the command
SetOperatingMode
is used. The value set using this command
can be read using
GetOperatingMode
.
A previously disabled current loop module may be re-enabled in a number of ways. If output was disabled using the
SetOperatingMode
command, then another
SetOperatingMode
command may be issued. If disabled as part of an
automatic safety event-related action (see
Section 4.8.9, “Current Foldback”
for more information), then the
command
RestoreOperatingMode
is used.
Current Control
Method
Brushless
DC
DC
Brush
Step
Motor
Individual Phase Control
(default)
Field Oriented Control
(default)
(default)
Third Leg Floating
Even when operated in the voltage mode, the user must still select the current control method. This is because
selection of this control method also affects aspects of the power stage, specifically the use of space vector PWM,
versus sinusoidal PWM, versus standard single-phase PWM generation.
The default condition of the current loop module is disabled, therefore to begin motor operations, the external
controller must send a
SetOperatingMode
command enabling the current loop module.
