I would like to investigate different modulation strategies for a 3-LVL-ANPC-SiC topology under different operating points in terms of overall efficiency and power dissipation (temperature) per switch.
To generate the switching points I use the carrier based PWM method (switching signals by comparing a sine reference voltage with 2 triangle comparative voltages). Same-side clamping, opposite-side clamping and full path clamping are used as modulation strategies.
The control of the switches and the generation of a three-phase sinusoidal current in the load works for the majority of the operating points under investigation. The occurrence of losses per switch is also in line with the values expected from theory.
In order to model the temperature-dependent R_DS_on of the Sic MOSFET, I set the Ron in Parameters to 0 and inserted a variable resistor, which uses a 2D look-up table to output a suitable Rds-on depending on the I_DS current and MOSFET junction temperature.
However, due to the variable resistor, I now get the following warning in every of the 18 switch models:
"Detected an algebraic loop comprising the following components:
As mentioned at the beginning, this is not a problem for the majority of operating points.
However, the warning above develops into the following error:
Could not solve the algebraic loop comprising the following components:
This leads to immediate termination of the simulation and occurs in particular at operating points with a very small power factor (=large phase shift) and always during the transient process in the very beginning.
Hence my question: is there a way to avoid the error or to change a setting so that the algebraic loop remains (warning) but can be solved?
I would really appreciate an answer. I have attached pictures to illustrate the problem.