Image 6.10: Expanded speed controller layout
The layout for this control scheme is shown in the figure above. It expands the
standard speed control circuit in such a way that the deviation between the n_set
setpoint and the n_eps actual value is fed through the integral term. This ensures
that the speed control circuit will be accurate in its steady state in regard to the
speed. In order to be able to continue using calculated speed n_kal, which is less
noisy and more dynamic, this speed is used for feed-forward control purposes. To
this end, the deviation between n_set and n_kal is added to the output from the I
controller via a proportional term.
Before being fed into the circuit, speeds n_kal and n_eps can each be smoothed
with a filter (P 351[0] for n_eps and P 339[0] for n_kal). The expanded speed control
circuit can be started with P 350[0] (“4” => Kalman)
MOOG
ID No.: CB40859-001 Date: 11/2020
MSD Servo Drive - Device Help
95
6 Encoder
P 351[1] can be used to implement additional scaling for the speed control
proportional term for the feed-forward control.
Measurements have shown that, when using the expanded control circuit, motors
with a marked saliency can be operated in a sensorless manner even without a test
signal.
6.8.1.4 Commissioning
The first step in commissioning sensorless control is correctly determining the motor
data and control parameters and configuring them accordingly. At this point, it is
especially important to ensure that the inductance difference between the motor’s d
and q axes is set correctly. This can be done with P 480[0] - MOT_Lsq. If this
parameter is not available (older firmware), P 472[0] - MOT_LsigDiff can be used to
set the difference as a percentage.
In order to obtain an accurate number, the values for the d and q inductances
should:
l
Be obtained from the motor manufacturer’s data sheet or the motor data set
OR
l
Be requested from the motor manufacturer OR
l
Be measured by Moog with an “advanced motor identification” routine OR
l
Be determined as an approximation for most motors with the motor
identification routine
If none of these options is available, it is possible to start with a rough setting of Lq =
110% • Ld for a test with a servomotor. However, you must then be ready for limited
operation within a narrow speed range.
The inductance difference is important when it comes to sensorless control, as the
Kalman filter can determine the position based on the inductance difference in
