Rockwell Automation 20B PowerFlex 70, PowerFlex 700 Reference Manual - Manual (Page 97)

Drive Overload
Rockwell Automation Publication PFLEX-RM001H-EN-P - June 2013 97
Thermal Manager Protection
The thermal manager protection assures that the thermal ratings of the power
module are not exceeded. The operation of the thermal manager can be thought
of as a function block with the inputs and outputs as shown below.
Figure 20 Thermal Manager Inputs/Outputs
The following is a generalization of the calculations done by the thermal
manager. The IGBT junction temperature T
J
is calculated based on the measured
drive temperature T
Drive
, and a temperature rise that is a function of operating
conditions. When the calculated junction temperature reaches a maximum limit
the drive will generate a fault. This fault can not be disabled. This maximum
junction temperature is stored in EE on the power board along with other
information to define the operation of the drive thermal overload function.
These values are not user adjustable. In addition to the maximum junction
temperature there are thresholds that select the point at which the PWM
frequency begins to fold back, and the point at which current limit begins to fold
back. As T
J
increases the thermal manager may reduce the PWM frequency. If T
J
continues to rise current limit may be reduced, and if T
J
continues to rise the
drive generates a fault. The calculation of the reduced PWM frequency and
current limit is implemented with an integral control.
PWM Frequency
PWM Frequency as selected by the user can be reduced by the thermal manager.
The resulting Active PWM Frequency may be displayed in a test point parameter.
The active PWM frequency will change in steps of 2 kHz. It will always be less
than or equal to the value selected by the user, and will not be less than the drives
minimum PWM frequency. When drive temperature reaches the level where
PWM frequency would be limited, the
Drv OL Lvl 1 Alarm is turned on. This
alarm will be annunciated even if the reduced PWM frequency is not enabled.
PWM Frequency
(2 - 12 kHz)
Output Frequency
(0-400 Hz)
Temperature Analog Input
(Volts)
DTO Select
(Off,PWM,ILmt,Both)
Current Limit
(0 - 200%)
EE Power Board Data
IGBT Temperature
(x deg C)
Drive Temperature
(x deg C)
DTO Fault
(On,Off)
Active PWM Frequency
(2 - 12 kHz)
Active Current Limit
(0 - 200%)
I_total
(Amps)
V_dc
(Volts)
ILmt Alarm
(On, Off)
KHz Alarm
(On, Off)
Drive
Thermal
Overload