7 Additional settings
Measures
Current peaks and, thereby, harmonics can be reduced by way of suitable measures. The
primary measure would be to increase the clock frequency. However, the clock frequency
cannot be increased to an unlimited extent as it is accompanied by higher switching
losses of the IGBTs that are used.
Servo drives made by Metronix enable a variable adjustment of the clock frequency in the
current controller circuit. In most cases, the clock frequency can be configured by way of
the Metronix ServoCommander
®
parameterisation program. In order to minimise
switching losses, the clock frequency of the pulse width modulation can be reduced by
half compared to the frequency in the current controller circuit. However, this does not
have a positive effect on the current ripple.
Another measure (to reduce current peaks) is to increase the motor inductance by way of
chokes. The chokes reduce the current ripple and, thereby, the stress on the motor
caused by harmonics. In some cases, the use of ferrite cores is sufficient for a strong
reduction of the current ripple.
To avoid damage to the motor (winding damage), these current harmonics should be taken
into consideration right from the outset. The current harmonics are added to the base
current (maximum current and nominal current). This is why the motor specifications
concerning the maximum and rated current must include the value of these current
harmonics.
In addition, external measures (see above) for reducing the current ripple are usually rather
expensive and time-consuming.
If these current harmonics are taken into consideration during the rating of the drive and
the parameterisation of the servo drive (maximum and nominal current limits), the risk of
damage to the motor can be minimised right from the outset.
Product manual BL 4000-C
Page 163 of 298
