User manual

Geo Brick Drive User Manual
Motor Setup 197
High Speed Motors
With Geo Brick Drives, motors conceived to operate at higher speeds (e.g. greater than 15,000 rpm)
require the implementation of commutation delay compensation Ixx56. This is also known as phase
advance. It only applies to motors commutated (synchronous or asynchronous) by PMAC.
Ixx56 permits the PMAC to compensate lags in the electrical circuits of the motor phases, and/or
for calculation delays in the commutation, therefore improving high-velocity performance.
The commutation delay compensation Ixx56 is best set up experimentally by running the motor at high
speeds, monitoring the current draw (e.g. using the current calculation PLC) and finding the setting which
minimizes the current draw of the motor without causing it to lose phase (typically triggering a fatal
following error or over current fault on the drive).
Example:
A DC brushless motor with a 2048 cts/rev encoder is desired to have a phase advance of 5 “electrical”
degrees at a speed of 30,000 rpm. The system is setup at a 4.5 KHz servo clock. The following equation
can be used to compute an empirical or a starting value for Ixx56:
#define ServoCycle 4500 ; Servo Clock [HZ]
#define Mtr4DesSpeed 30000 ; Max desired speed [rpm]
#define Mtr4EncSF 2048 ; Motor #4 Scale Factor [cts/rev]
#define Mtr4PhaAdv 5 ; Motor #4 Phase Advance Angle [electrical deg.]
I456=Mtr4PhaAdv*2048*60*ServoCycle/(360*Mtr4DesSpeed*Mtr4EncSF*96*32)
Note
This parameter is especially useful with motors commutated over a
Macro ring.