When using PLECS 4.7.4 software to perform thermal simulation on the inverter, I found that the temperature of the device would continuously rise to infinity. However, I removed the relevant settings for thermal simulation and only performed electrical simulation, and the circuit was running normally. I would like to know how to handle this issue so that my thermal simulation can run normally.
You have correctly diagnosed the problem in that you have thermal runaway in your circuit. There are several factors that can contribute to this. Ensuring the electrical model is reasonable is a good first step. Without a model it is difficult to debug. Furthermore it could be a simulation error (e.g. incorrect entry of thermal impedance, your upper and lower H-Bridges are not on a common heatsinks) or a design issue (you are not using an appropriately rated device or require a bigger heatsink).
I can provide the following general guidance:
- Are your devices rated appropriately for your circuit based on the switch stress?
- Are the device thermal impedances reasonable given the datasheet?
- Is the “Thermal Chain” component in your model appropriate or is the thermal resistance too high?
- Where is the thermal model from? Did you develop it yourself or are you using a vendor supplied model? Do the conduction and switching loss values make sense given the data sheet specifications?
- Could there be a unit scaling issue (e.g. switching loss unit is Joules instead of mJ or uJ)?
- Is the thermal structure correct (i.e. upper and lower bridges are not on a common heatsink)?
- Is there an electrical transient at startup that could over-stress the devices beyond their safe operating area?
See this forum post as well for guidance.