Need Help using buck-boost converter to power a simple motor armature circuit

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miskeenooo

Joined May 2, 2025
1
So I know this is probably a simple problem, or not even a problem at all, and as you can probably see I'm still starting to get familiar with these concepts, however, in my head this is not making sense. My problem is that after I configure my buck-boost converter probably to give me 30V from a 12V source properly on a 15 ohm load, I attach my motor armature circuit and that voltage starts acting weird on the output load, and at the armature resistor. I've also tried using a non-inverting buck-boost, but it gives me even less voltage current which is even harder to solve. I've alternatively tried to invert the voltage at the armature but to no avail, by inverting the terminals, which doesn't make sense since the current that goes through is positive. I am going to put pictures of what I'm describing under this:
Screenshot 2025-05-02 at 12.00.03 PM.png
This is the picture of the output of the converter (without simple motor armature attached) at 0.7 duty cycle.
Screenshot 2025-05-02 at 12.03.06 PM.png
This snapshot shows my specific error. V-out voltage shape makes a little sense in my head since it behaves like a third order system (I believe) and is fine I guess. The problem is I am not getting close to my boosted voltage, and it is still negative which will spin the motor the opposite way. This project is just me trying to see how I would design a simple working motor arm, I already mechanically designed it but I am still working on the electronic and control.
Screenshot 2025-05-02 at 12.21.24 PM.png
This is another snapshot of the non-inverting buck-boost. At this point I've tried everything and I'm starting to thing it might be a complete ideological or design flaw from my end.
 

MisterBill2

Joined Jan 23, 2018
27,311
I am guessing that the intention is to power a motor that requires a 30 volt supply with a switching boost regulator powered by a 12 volt source. I am guessing that the motor is represented as that 15 ohm load, meaning it requires two amps from the 30 volt boost regulator supply.
BUT the circuit shown presents a 15 ohm load in parallel with the motor equivalent circuit, (which does not seem to be correct.)

First, the design of switching regulators is complex, and second, the representation of the motor does not appear to be correct either, which will be a flaw causing problems with the evaluation.
 

schmitt trigger

Joined Jul 12, 2010
2,056
Your motor model is incorrect.
At zero RPM, the back EMF is also zero and slowly ramps up. Change the voltage source to reflect that fact.
Also the motor’s inductance is in series with the resistance.
EDIT; what I meant is that the 15 ohm resistance is superfluous
 
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