Accelnet Plus Micro Modules User Guide
16-01687 Rev 03
Copley Controls
Page 114 of 139
C
OMMUTATION
M
ODES
The drives support three commutation modes to drive brush and brushless motors:
•
AC brushless sinusoidal: U-V-W PWM outputs are sinusoidal with 120 degrees of separation
•
DC brushless trapezoidal: U-V-W PWM outputs DC values at 60 degree increments
•
DC brush: U-V outputs are DC values from the maximum positive and negative ratings
In most applications, sinusoidal commutation is preferred over trapezoidal, because it reduces
torque ripple and offers the smoothest motion at any velocity or torque. In the sinusoidal
commutation mode, an encoder is required for brushless sinusoidal commutation. Halls are
sufficient for trapezoidal commutation. When driving a DC brush motor, the drive operates as
a traditional H-Bridge drive. All of the commutation modes are used to produce current in the
motor resulting in acceleration of a load.
F
EEDBACK
All of the
Accelnet Plus Micro Module
drives support digital quadrature encoders, analog
Sin/Cos encoders, and a variety of absolute encoder formats. They typically use Hall sensors
for the commutation of brushless motors when incremental encoders are used. Without Halls,
algorithmic phase initialization (aka ‘wake ‘n shake’) occurs when the drive is first enabled.
Absolute encoders can be auto-phased using CME and the results saved in the drives flash
memory, eliminating the need for Halls. Brush motors are self-commutating and do not
require feedback for torque production.
S
YNCHRONIZATION
Using EtherCAT, the distributed clock feature can be used to establish PWM switching
frequency synchronization among the network connected drives. Typically one drive acts as
the Sync 0 reference clock. The master then adjusts the Sync 0 frequency and phase in the
slaves to so that they are all in-sync.
Over CANopen, one drive produces a Sync message that carries a high-resolution time-stamp.
The other drives on the network receive the Sync message and adjust their internal clocks so
that all of the drives on the network have their PWM frequencies synchronized.
