I have a 3 phase system, with parallel switches in play. I have the same model with different FET thermal profile which runs without an issue but this one seems to be giving the error as mentioned in the title with nothing else changes apart from the thermal files.
i have gone over the thermal [properties side by side and cannot seem to understand what might be causing the issue
The issue is that your are experiencing thermal runaway. See this note in the PLECS Error Messages documentation, which highlights the same issue albeit which can manifest in different errors. I can see that some of your FETs hit a temperature of 1e14 degrees, upon which the error occurs.
The issue is in the MSC020SMB120DS model you have developed. Unfortunately that part doesn’t have a PLECS model and I’m not certain how you developed the associated model as the data sheet is missing several key parameters. However a very similar part does MSC020SMB120B4 have a PLECS model provided by Microchip. Perhaps compare the two devices and determine if that is a suitable replacement. Even so, a “good” thermal model can experience thermal runaway under extreme operating conditions.
Thanks for that bryan, I managed to use the thermal model for MSC020SMB120B4 directly as it is a discrete version of the die that I am using and will be suitable for my investigation. no thermal issues now.
i also dont seem to be getting any current flowing through the parallel IGBT for some reason. is there anything i am missing there as the electrical connections seem to be fine and the gate input seems to be showing signals going to both the FETs and IGBTs and intended
The electrical parameters in your model define how the currents are shared between the devices.
See this minimal example which produces the graph below. The MOSFET will carry all the current until the voltage drop across the FET exceeds the forward voltage of the IGBT after which the currents will be shared in proportion to their on resistances. In your model the effective MOSFET resistance is 6.67 mOhm and the IGBT forward voltage is 0.85 V, so the current sharing begins at 127.5 A. current_split.plecs (9.2 KB)
Also, note PLECS 5.0 and above there is a native “Number of parallel devices” parameter in the Thermal tab for MOSFETs, Diodes, and MOSFET with Diode components. This parameter is used to simulate the effect of connecting multiple identical devices in parallel while adding only one single switch element to the electrical system equations. See the PLECS Documentation and the documentation of these components for further information and a simple minimal example.
