About behavior of thermal switch model

Yongjun

If IGBT in the attached psimsch file is simulated with a thermal model, the current appears to be on/off at level 0.
However, the voltage waveform cannot be switched at the 0 level and seems to be switched at the level of 0.7~8V. Ideal switches do not have this phenomenon, but the thermal model used in this circuit diagram file and other thermal models show similar voltage waveform characteristics.

Even if you don't input anything in the temperature pin, it works the same way, why?

Does the behavioral characteristics according to the purpose of using the Thermal model cause this situation?

IGBT_sw_char_test -.zip

Rhonda_20369

Hi, Yong Jun,

In your schematic, the ideal model has the parameters:

Saturation Voltage =0. 

Transistor resistance = 0.

Diode Forward Voltage = 0.

Diode Resistance = 0.

Therefore, when either the transistor or the diode is conducting, the voltage=0, as it should be.

 

When you use a thermal model, those parameters are defined by the curves in the thermal database. Those curves are from the graphs provided in the manufacturer's datasheets.

 - When the transistor is conducting, the curves in the graph "VCE(sat) vs. IC" defines the voltage at the transistor junction. 

 - When the diode is conducting, the curves in the graph "VF vs. IF" defines the voltage at the diode junction.

 

In the thermal model, the conduction losses of an IGBT are calculated from those curves. 

You may find the basic functionality of the thermal models in a short video tutorial in PSIM's "Help >> Video Tutorials >> Overview and Getting Started >> Introduction to Thermal Module".

 

Sincerely,
Rhonda