Corrected from:- Inverter Drives 8400 StateLine V13.00.00
- Inverter Drives 8400 HighLine V13.00.00
- Inverter Drives 8400 TopLine V13.00.00
Response of the new version:
The function restriction has ben resolved.
Which products are affected?
Inverter Drives 8400 StateLine, HighLine, and TopLine up to the firmware version 12.01.00.00
What happens?
The quantisation (smallest representable change) strongly increases with an increasing inertia and/or acceleration.
The torque setpoint LS_Motorinterface.nInputTorqueCtrl_a toggles around the expected mean value. It is presumably noticed that the drive emits audible control noises when accelerating/decelerating.
When does the problem occur?
The feedforward control torque is generated from the product of the moment of inertia x the acceleration (J x α). The quantisation is maximal in the case of very low accelerations and great moments of inertia.
Example: In the case of an acceleration time t_acc=2s, acceleration time for n_Set=0..100%, and an inertia of 200kgcm², the minimally representable change in the feedforward control torque is approx. 10% of C57. In the case of acceleration times in the range of t_acc=10s and 200kgcm², the quantisation is already approx. 36%.
The behaviour will typically occur in the case of applications with great moments of inertia with a moderate acceleration.
Diagnostics options?
The feedforward control component can be diagnosed best by recording the torque setpoint LS_Motorinterface.nInputTorqueCtrl_a.
Tip: With a very low gain in the speed controller, the impact of the feedforward control in the torque setpoint becomes more distinct.
Changing one of the two factors (J or α) has a direct effect on the quantisation of the signal.
Short-term measures/recommendations?
None. In applications with 8400 HighLine or TopLine, an acceleration feedforward control can be alternatively generated by differentiation of the setpoint speed with an L_DT1_1.
Evaluation:
With increasingly lower accelerations, the quantisation steps in the feedforward control increase. The torque feedforward control cannot be used for lower accelerations. The behaviour will typically be detected during commissioning.
