Drive Overload 2-73
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 2.10 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 temperature device is inside the power
module T
Drive
is the same as T
Case
. On larger size drives the temperature
device will be mounted on the heat sink rather than inside the power
module, and the thermal model becomes more complex.
P
J
as defined in the second equation is the power dissipated in one
generalized IGBT.
R
J-Case
is the worst case thermal resistance from the junction to the case.
Boost[freq] is a term that increases the modeled temperature at low output
frequencies.
kHz * SwitchLosses is a term that increases losses at higher PWM carrier
frequencies.
T
J
= T
Case
+ P
J
R
J-Case
Boost{Freq]
P
J
= I
Peak
2
R
0
+ I
Peak
V
0
+ I
Peak
V
DC
kHz * SwitchLosses
Without a temperature device on each IGBT the calculation of T
J
must take
into account the worst case conditions for heat transfer. A model that adds
the heat dissipated in the rectifier is also under consideration. More detail
will be included in the design specification.
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
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