IGBT Thermal Modelling - Junction temperature exceeded error in PLECS blockset

Question

Hi.

I am quite new to thermal modelling with PLECS but started off with a simple model that behaves like a simple chopper with a 800V DC input and 20ohm resistor acting as a load. I am generating the PWM signal in the Simulink environment using a PWM generation block with a switching frequency of 15kHz and duty cycle 0.4.

The thermal model I am using for the IGBT is IKY50N120CH3 by Infineon. I found the PLECS thermal model on their website and decided to use it as an example.

However, when I try to run the model, I get an error stating that "The junction temperature (175.006) is greater than the upper limit specified in the thermal description (175)".

I'm confused why this is happening as my voltage (800V) is less than the device rated voltage (1200V) and my current in the circuit is also less than rated current. I do not know why the temperature goes beyond the maximum in this case. Is there anyway of externally keeping the junction temperature constant in PLECS?

I have attached the thermal description file I am using and a screenshot of my simple chopper along with the error message. Can someone please tell me what is causing this and how I fix it?

Answer 1

We would need your model to provide specific feedback on the cause of the Tj rating being exceeded. However, from the images, I can tell you that a thermal resistance of 1 K/W may be too high to allow the heat to sufficiently flow from the IGBT to the ambient environment. But to answer your question, you can remove the Rth and ensure that the heat sink has no thermal capacitance and then fix the heatsink to a specific temperature, e.g., 25C.

Comments

Although, this works for the example model I have specified here, it exceeds the temperature again when I try to use it in a different model.

I have shared my model with PLECS support to find out more. Thank you for your help!