Operation
Atlas
®
Digital Amplifier Complete Technical Reference
53
4
Figure 4-9:
Power Stage
Control Flow
In addition to the output bridge function, Atlas provides a current measurement function for use by the current loop
module as well as by the safety processing module. Two channels of phase current feedback are provided for brushless
DC and step motor current loops. For DC Brush motors feedback for one phase is provided.
Three selectable control methods are provided; independent phase, field oriented control, and third leg floating. The
choice of control method affects the power stage in the selection of the PWM generation technique. The table below
shows this.
To select the control method use the
SetCurrentControlMode
command. To read the value set using this command
use
GetCurrentControlMode
.
4.6.1
PWM Output Limiting
In some applications it may be desirable to limit the maximum allowed output of the power stage PWM generator. For
example if the bus voltage is 36 volts, and the desired voltage limit for a particular motor is 18 volts, a PWM limit of
50% is programmed.
Control Mode
PWM Output Method
Independent Phase
sinusoidal
Field Oriented Control
space vector modulation
Third Leg Floating
standard single-phase
Depending on the Atlas unit bus voltage and the effective inductance of the system being controlled, under some
circumstances lowering the maximum PWM duty cycle may not fully limit the effective voltage experienced by the
device. If this is the case for your system, you may consider increasing the Atlas unit PWM frequency, adding an
inductor to the motor circuit, or consulting a PMD representative for more information.
PWM
Control
PWM output
selection
Clock
A
B
C
D
• sinusoidal
• space vector
• single-phase
Phase A
Phase B
Voltage
command
from
current loop
or SPI
interface
Only
A bridge
shown
for clarity
to
coil
AH
pre-
driver
AL
pre-
driver
PWM
bridge
signal
generator
+HV
Mtr_Gnd
