I have made a DC motor circuit whose output is supposed to be controlled by the duty cycle of a PWM.The PWM sets the duty cycle of a transistor which sets the gain of the buck-converter.The program runs fine on Multisim until at around 40 ms where the program stops working and the armature current goes to some absurd value which obviously is not correct.What am I doing wrong?

 

I suggest running the simulation in a step-by-step mode to see what goes wrong..

 

I think its a bug.

 

You posted a zip file of a multi sim National Instruments file (ms14) which since I don't use anything NI since I retired I can't open or view. Unless someone else here is running multisim they can't view the file either.

Ron

 

THAT explains why I could not view the file.!!

 

You posted a zip file of a multi sim National Instruments file (ms14) which since I don't use anything NI since I retired I can't open or view. Unless someone else here is running multisim they can't view the file either.

Ron

Ok I thought many people were using Multisim here but I guess I should upload a schematic.

 

 

And the graph looks like this

and I dont know what it does the jump towards top at the end.

 

Look

 

Look
View attachment 366354

Could you seperate the 2 imags and enlarge them?What is wrong with my circuit?Is the polarity of I1 wrong?

 

Ok I thought many people were using Multisim here but I guess I should upload a schematic.

"Many People" is a very long way from "everybody", and certainly a whole lot of us do not have multi-sim, or even other simulators on our home systems.
AND, that most current posted circuit, with the transistor shunting the field coil supply of the motor, would not ever pass my design review.

 

Into this former lovely flower garden, in 2018, wandered cow.
And now all around is covered by numerous cow pats in few layers...