KEB COMBIVERT F5, Reference Manual, Page: 210 / 349

210
LX - Special Function Parameters
This function is designed to protect the inverter from dangerous currents when
operating at very low output frequencies. Depending on the motor design, the
drive may be forced to provide high currents at output frequencies below 3 Hz.
This causes considerable thermal loading on the power transistors. To protect
itself, the drive will monitor the load current when operating at or below 3 Hz.
If the drive’s rated stall current limit is reached, the drive will display “Error Low
Speed Overload” and stop operation.(See section 2.10)
With LX07 turned off, the F5 will trigger the low speed overload error when the
stall current limit is reached. However, the F5 can also be set to automatically
lower the switching (carrier) frequency when the output current reaches the stall
current limit. By doing so, the stall current threshold is raised. This prevents the
Error Overload Low Speed from occurring; allowing the drive to keep running.
Alternatively, the temperature of the power transistors can be monitored by
the drive to control the stall current threshold. At lower temperatures, the stall
current limit is raised allowing more current t
o flow before triggering the error.
The drive can also adjust the stall current threshold using both Switching
Frequency Management and Heatsink Temperature Dependence.
Settings: NUM
Off 0
Switching Frequency Management 1
Heatsink Temperature Dependence 2
Switching Freq. Mgmt.+ Heatsink Temp. Dependence 3
Default = Switching Freq.+ Heatsink Temp. Dependence (3)
This parameter can be used to select what type of current check is performed.
If Phase Current Check is selected, the Magnetizing Current Check will also
be performed for induction motors.
In the event there is a problem getting a consistently positive phase current
check, the user will see ‘Error Low Motor Current’. It is possible to select
only a magnetizing current check but this setting should only be used on
construction mode as the code requires a check of all phases before automatic
operation.
The process is initiated at the beginning of a run with the drive enable and a
direction input. The phase current check completes in approximately 300ms.
Settings: NUM
Magnetizing Current Check 0
Phase Current Check 1
Default = Phase Current Check (1)
LX07
Carrier Frequency
Handling
LX08
Phase Current Check