I don't have PSpice so I found

this online which only works if you enter the inductance and try increasing values for current until the result = 12.001 V and the value for current that obtains that result is the 1091A you cited.

In all honesty, math was never my strong suit. I learned basic electronics math including algebra but deriviatives is something I studied at DeVry but never mastered and frankly , don't remember.

I did find

this, which helps, but frankly I am having a hard time grasping how the math can explain the typical ringing waveform you see across an inductor. I can generate that waveform and observe it on my scope,

(which I have done and taken photos of : see attached) but as yet , I don't understand how the math explains or describes the ringing seen in the photo.

One of the things that I am trying to understand (again) is:

You can see according to this formula that the voltage is directly proportional to the derivative of the current. Since the derivative of a constant is equal to 0, if the current is a direct current (DC), the current across the inductor will be equal to 0. So if the current is a DC current, the current flowing through the capacitor will always be 0. This, again, is because the derivative of a constant is always equal to 0. A constant does not change. So if a user simply enters in a current such as 10A or 20A or 30A, the current will be 0, for all these values. This shows that no voltage can be across an inductor if it is connected to a DC power source. There is only voltage across an inducttor when it is connected to an AC source.

It seems to me the above statement does not take into account the case of turn on and turn off.Since the OP's motor is a DC motor , Reactance does not apply, and Cos(t) does not apply.

In the attached schematic, how should the diode or diodes be connected ?

@DLoyd,

Sorry about the price tag but this is an old photo taken before I removed the price tag.