Page 15
IronHorse GSD8 DC Drives User Manual – 1st Ed. Rev. A – 10/15/2019
Basic Operating Instructions
Control Algorithm Discussion
GSD8-240-5C
The GSD8-240-5C DC drive controls are based on a pulse-accumulation algorithm. The advantage of
this algorithm is that it allows the GSD8 drive to follow a master process with exceptional accuracy.
The GSD8 drive has three parameters which allow the user to adjust how tightly the GSD8 drive will
control the motor to achieve the target speed. These 3 parameters are as follows:
•
P Gain - Is the proportional gain for the control loop. In pulse-accumulation algorithms, there is no
error on which to calculate proportion output response; therefore, the GSD8 drive estimates error
based on several factors. Those familiar with PID tuning should be aware that the GSD8 drive’s
P Gain is different than that of typical velocity control PID algorithms. P Gain is a function of the
instantaneous error between the target (desired) speed and the present speed of the motor.
•
I Gain -This is the integral gain for the control loop. The I Gain is a function of accumulated error, a
measure of the difference between the target (desired) speed and the current speed of the motor.
•
Pulse Accumulation Limit - This parameter allows the user to limit the maximum number of pulses the
drive will accumulate prior to intentionally losing count and therefore long-term accuracy. See the
details for parameter 29 in the Parameter Description section.
All other GSD8 Drives
A true P-I-D speed control algorithm is employed in the GSD8-240-5C-D, GSD8-240-10 series, and
GSD8-10N4X series drives which allows precise and quick response to set speed or load changes.
Three parameters, 26, 27 and 28 (Proportional, Integral, Derivative, respectively) are adjustable as
shown in the parameter table on page 24. P-I-D can be tuned to get precise speed response and
regulation.
When adjusting P-I-D, begin by using the factory defaults: Proportional (parameter 26) to 150, Integral
(parameter 27) to 20 and Derivative (parameter 28) to 10. If further adjustment of P-I-D is needed,
follow the steps below.
•
To adjust Proportional (Parameter 26):
Run the motor from zero speed to the set speed. If the start up response of the motor is too slow,
increase “P” in increments of 20 until the desired start up response time is obtained. If the start up
response time is too fast, decrease “P” in increments of 10 until the desired response is reached. “P”
is used to adjust the start up response time only. The start up response time is approximately 0 to
60% of the set speed. “I” can be used if adjustment of the upper response time (60 to 100% of the set
speed) is needed.
•
To adjust Integral (Parameter 27):
Run the motor from zero speed to the set speed. If the upper response time (60 to 100% of the set
speed) has any hesitation or has too slow of a response, then increase “I” in increments of 5 until the
hesitation is eliminated and/or the desired upper response time is obtained. If the upper response
time is too fast or has too much overshoot, decrease “I” in increments of 3 until the overshoot is
eliminated and/or the desired upper response time is reached.
•
To adjust Derivative (Parameter 28):
“D” can be used to dampen the effect of “P”. By making “D” too large, the response time of the
control can be reduced, so keep “D” as small as possible on non-regenerative controls.
NOTE: The overall proportions of each P-I-D parameter seems to be more critical than the individual
values, i.e. values of 50-50-50 will achieve virtually the same results as 999-999-999.
Pulse-Accumulation Loop PI Tuning
Many applications do not require tuning of the P and I Gain parameters beyond the supplied factory
default settings. If more responsiveness is desired or if the motor oscillates an unacceptable amount
when changing speeds, it may be necessary to adjust the P and I gains to obtain optimal performance.
Increasing the P and/or I gains will cause the control to drive the motor more aggressively. Decreasing
the P and/or I gains will cause the control to perform more sluggishly. Properly tuning the P and I
gains encompasses more than independently adjusting the P and I. The ratio between the two is very
important as well. Although initial tuning can be a time-consuming task, here is a basic outline of how
to proceed:
