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Unidrive User Guide
97
Issue Number: 9 www.controltechniques.com
8.1.3 Servo motor control
Pr 0.46 {5.07} Motor rated current
Defines the maximum motor continuous current
The motor rated current parameter must be set to the maximum continuous current of the motor to ensure the current limits in the drive function at
the correct levels so that the motor is protected should an overload situation occur.
Pr 0.42 {5.11} Motor number of poles
Defines the number of motor poles
The motor number of poles parameter defines the number of electrical revolutions in one whole mechanical revolution of the motor.
Pr 0.40 {3.25} Autotune
The motor should be stationary and disconnected from any load
(including the gearbox) before commencing an autotune.
The test rotates the motor by less than a revolution. The exact distance
depends on the number of motor poles.
The autotune measures the offset between the feedback device zero
and the rotor zero. This is required so that the voltage applied is in phase
with the back EMF from the motor.
If the value entered is incorrect the drive will not control the motor
correctly.
The result can be:
1. loss of torque
2. excessive heating of the motor
3. in extreme cases the motor can run out of control to maximum speed
If the load cannot be removed and it is solely an inertia a high current
autotune can be enabled.
Set Pr
5.27
= 1 prior to enabling the autotune.
Pr 4.13 / 4.14 Current loop gains
The current loop gains control the response of the current loop to a change in current (torque) demand.
The default values give satisfactory performance for most applications however for optimal performance in dynamic applications the values may
require tuning for the specific motor.
Inappropriate values entered in these parameters can cause the control system to become unstable.
The current loop gains can be calculated from the motor resistance and inductance values by either:
1. Using the formula detailed below
2. The gain calculator wizard in Unisoft version 3.43 in the ’Tools’ menu
The proportional gain (Pr
4.13
) should be set to 1800 x
L
x 10
-3
x Pr
11.32
where:
L
= per phase motor leakage inductance (mH) (from the motor data sheet)
Pr
11.32
= Drive rated current
The integral gain (Pr
4.14
) should be set to 0.044 x Pr
4.13
x
where:
Pr
4.13
= current loop proportional gain calculated above
R
= per phase stator resistance (from the motor data sheet)
L
= per phase motor leakage inductance (mH) (from the motor data sheet)
For very small servo motors with high inductance the values calculated from the above formulae can be too high resulting excessive motor noise.
The values should be calculated and then reduced to a suitable level manually.
0
0
R
L 10
3
–
×
---------------------
NOTE
Summary of Contents for Unidrive 1 Series
Page 208: ......
