PowerTec 2000C Instruction Manual page 19

ABOUT POWER POWERTEC POWER POWER POWER
Page 1-12
pulses, the count is negative, and the motor current will be shut off
(the motor will coast along) until the accumulated count becomes
positive again.
A motor running at no load will accumulate only a few pulses
of position error, but a fully loaded motor will accumulate 2/3 of the
pulses necessary for current limit. Loads between no load and full
load will accumulate some number between 0 and the full load
value. The maximum number of error pulses which may accumulate
is about 100 (this is an adjustable "gain" function) at which time the
brushless drive will be in current limit. When the maximum number
of pulses are accumulated, the control is in current limit and further
reference pulses will be ignored until the motor turns far enough to
eliminate the excess pulses in the counter.
As long as the current limiting condition is avoided, the motor
can track the reference frequency pulse for pulse. IT IS IMPOR-
TANT TO NOTE THAT, SHORT OF CURRENT LIMIT, THIS
PULSE ACCUMULATION DOES NOT AFFECT SPEED. It only
affects the shaft position relative to the no load shaft position. Most
motors talk about speed regulation in terms of revolutions-per-
minute difference between set speed and actual speed. A Brushless
DC motor set to run at 1750 RPM (with a frequency reference), will
be running at 1750 RPM, period.
For motors operating at a steady speed and at a steady load, the
pulse accumulation will not change but will stay at the value neces-
sary to drive that load at that speed. If the load should change, the
pulse accumulation in the up/down counter will change to a value
necessary to drive the new load. If the speed changes, the pulse
accumulation will not change if the torque required by the load is
the same at the new speed as the torque required at the old speed.
This is a brief, very simplified introduction to the operation of
Brushless DC motors. It does not and cannot cover all the points
necessary for a full or complete understanding. There are books
available on the subject of Brushless DC motors.
POWERTEC manuals contain a great deal of information and
further understanding will come also with use of the motors and
controls.
POWERTEC Industrial Corporation manufactures Brushless
DC motors and controls for the industrial environment. Other
manufacturers produce Brushless DC motors for some specialized
applications, but only POWERTEC makes a full line of Brushless
DC motors and controls from fractional to 600 horsepower for use
on industrial power sources (230, 380, and 460VAC three phase) in
standard NEMA (National Electrical Manufacturers Association)
frame sizes at prices competitive with conventional DC and Adjust-
able Frequency AC, including vector.
Model 2000C/3000C Instruction Manual