Hello. I have a network with number of VSDs which I did modelled in Digsilent and getting an error of System Matrix Inversion Failed when I run a RMS/EMT study to check how the motor starts as well as how the speed is controlled. There is also a warning that says " No convergence. Maximum number of inner loop iteration for network model equations has reached". Is it Possible to run the RMS/EMT study when multiple VSDs are part of the network?
I have many induction motors as well as part of the network because the network represent the mining area. Any help regarding this would be much appreciated.
Thank you Srete. The slack bus is well defined and if I run the normal load flow or harmonic load flow I'm not getting any error. I have a concern as I'm analysing the harmonic and I cannot tell how the speed of the motor is being controlled by the VSD. Once I run the EMT for the VSD then I get this error.
If you have an official licence you can send and open Ticket on DIgSILENT Support and send the file. You will get answer in one day. BTW which version do you use? Srete
I'm currently using a thesis license 2019 version. I will discuss with DIgSILENT support team. Thank you.
Please share the answer you received from the DiGSILENT Support team experts!
Hello Srete, I did not receive an answer from them yet, once received I will be able to share. Thank you.
Thanks to Prof de Kock of NWU who explained to me that this error can be caused by numerical instability and also relate to integration step size which is either too large or too small.
This gave me an idea to search more about the step size. My first approach was to increase the integration step size of the electromechanical transients from 0.01 second to 0.1 but the error remained and number of warning was much more than before.
Secondly, I decreased the step size to 0.0001 second. I am currently not getting any error and the motor is starting perfectly normal and the VSD is controlling the speed as per speed control parameter that I set for the case study.
Thanks to Rosalia answer, I can solve my problem with same approach. Even if I run ComSimwith RMS, the setting is located in ComInc. Using Python API, the solution is:
oInit = app.GetFromStudyCase('ComInc') # initial condition calculation object
oInit.dtgrd = 0.05 # step size (in ms)
Sadly, this make the generated files too big (around 2GB)
Hello Muhammad, good to hear that with this approach you are able to solve some problems. I didn't notice that the size of the file changed.
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