Hi Faringdon,
I am not sure what you are trying there. It looks like an attempt to measure the peak value of the current pulses,
in the presence of a high DC offset, without introducing impedance to the circuit.
My comment would be that is usually this is not feasible with any known ferro magnetic cores.
If the core is driven into magnetic saturation ( tending to U_effective =1 ) due to the long term "average DC" in the primary, then the core ceases to have any effective function on the AC electrical side.
That is, the primary and secondary can be considered to be coupled by air. So the core can be removed without much effect.
Without going into integrals etc, using SI units you can use these on the simplistic DC analysis of core:
H = N*I /length_effective [A/m]
and similiar to the above:
phi = N*I/ ( Reluctance _Ferrite + Reluctance_airgap) [Wb]
B = u_effective * H. [T]
and similiar to the above:
B = phi/Core_Area
Ferrite toroids usually go into hard saturation at B > 0.3 to 0.4 Tesla.
references for above include DC choke design, C/T design with DC offset allowance, and my favorite ferrite reference book, Snelling (section 4.2.2 +more)
Other ways to measure, could be a sensing resistor, a high-side differential amplifier, , Hall effect device, and Rogowski coil.