Carrier Frequency Derating and
Current Limitation
6
Carrier Frequency Setting
The carrier frequency selection has a direct influence on the motor noise. The higher the carrier frequency the lower is the motor noise. On the other hand the overload capability of the inverter is reduced with a higher carrier frequency. Both have to be considered when the setting is changed.
Related Parameters
Parameter
No.
C6-02
Name
Carrier frequency selection
Factory
Setting
3
Change during
Operation
No
V/f
Q
Control Methods
Open
Loop
Vector
Q
Closed
Loop
Vector
Q
Closed
Loop
Vector
(PM)
Q
Carrier Frequency Selection
The factory setting is 8 kHz for units from 3.7 to 22 kW and 5 kHz for units from 30 to 55 kW. Usually the value has not to be changed. However, if it necessary to change it, observe the following precautions:
•
•
If speed and torque oscillate at low speeds: Lower the carrier frequency.
If inverter noise affects peripheral devices: Lower the carrier frequency.
•
•
If leakage current from the Inverter too is large: Lower the carrier frequency.
If metallic noise from the motor is large: Increase the carrier frequency.
Carrier Frequency and Inverter Overload Capability
If the carrier frequency is increased the rated current is decreased and vice versa (refer to
page 9-6, Carrier
Frequency Derating
). The overload capability is always 150% of the derated inverter current for 30 sec. If this
over load limit is exceeded the inverter trips with an inverter overload fault (OL2).
Current limitation level at low speeds
The Varispeed L7 limits the output current at low frequencies. This current limitation does not change with the carrier frequency selection. The current limitation in the low frequency range is as follows.
150%
140%
130%
120%
110%
200V Class 15kW
400V Class 30kW
200V Class 3.7, 18, 30kW
400V Class 18, 22kW
200V Class 5.5kW
400V Class 3.7, 5.5, 7.5, 11, 55kW
200V Class11kW
200V Class 7.5, 22 , 37, 45, 55kW
400V Class 4.0, 15, 37, 45kW
0
Output
Frequency
1.5Hz
3Hz 4.5Hz
6Hz
Fig 6.1 Low frequency current limitation
IMPORTANT
• If the torque at low frequencies is too low, check whether the current runs into the limitation explained above. If so, check the motor data settings (E2-
) and the V/f pattern (E1-
).
• If the current still runs into the limit it might be necessary to install a one size bigger inverter.
• For selecting an inverter please consider the low frequency current limit as described above and select an inverter with an appropriate current margin.
6-
2
