3BHS135824 ZAB E01Rev. D 59 (of 62)
13.2 Final Tuning of Speed Controller
The next step is to make the final tuning of the speed controller. The
idea is to get the drive performing as well as required by the driven
process. The main requirement is not to make the control as fast as
possible, but only fast enough to make the changes required by the
process, without conflicting with other control loops. Too fast speed
controller may cause unnecessary stress on the mechanical system
(gearbox, belts, etc.).
The tuning must be checked under different load conditions and over
the whole speed range. When carrying out tuning under actual load
conditions, the values obtained during pre-tuning normally need
readjustment.
Some methods to tune the speed controller are given next but methods
other than those presented in this chapter can also be used.
Speed steps of 2% of maximum speed or bigger are applied to see the
response behaviour of actual speed. See instructions for speed step
tests and for monitored signals in the previous section 13.1 Preliminary
Tinung of Speed Controller.
The integral time constant 24.08 TIS is reduced until overshoot is
observed in the response. The integral time constant is then adjusted
such that there is no overshoot or only a slight overshoot (depending on
the drive application). The function of the integral part is to remove as
quickly as possible the difference caused by the proportional control
between the reference and the actual value. If the drive is stable and
allows a high proportional gain, the integral time constant can be set
short and an overcompensated step response is obtained.
If the drive goes to the torque limit in a step, a further compensation of
the response should not be attempted.
See Figure 13-1 for different kind of step responses.
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