Inductance saturation measurement L(I)

Question

Hi,

i would like to model saturable inductors / transformers in PLECS. For validation I would like to build a "measurement" circuit to evaluate the L(I) saturation curve of the implemented model against real world measurement data.

First I try to use prebuild block like Saturable Inductor as a simple example.

To measure the L(I) I use a step function voltage source supplying the inductor, current measurement through the inductor and voltage measurement accross is. To verify the resulting saturation behaviour L(I) do the math calculation u=L*di/dt --> L=u*dt/di and plot it in a XY Plot with x=i, y=u*dt/di.

As I found out, PLECS does not implement a time derivative block of a signal and hence I implemented C-Script proposed on the PLECS website to calculate the time derivative of i(t) --> di/dt.

At the end of the excercise there is no L(I)-curve visible in the XY Plot. Any ideas how to measure the L(I) in PLECS in a better way?

Of course the Saturable Inductor should be trivial and not such validation in an XY Plot should be needed, but then with the correct measurement setup in PLECS I would like to verify a more sophisticated saturable reluctance model in PLECS against real world measurements.

So if there are some experts out there how know how to model and validate saturable reluctance models in PLECS, I would appreciate some help. Thanks.

Answer 1

Using derivatives in measurement is generally subject to noise and can create poor results.  For example if the scope is blank, the result is likely not a number or infinite (NaN/Inf).  One can create a bandwidth limited derivative block using the transfer function s/(s/Kf+1). See this other forum response related to the PID block.  This somewhat works, per the attached model, but I would not recommend it for the above reasoning.  There also could be an integral based reformulation of your query, but I didn't implement such a change.

A better way would be to use the time constant of an RL circuit and look at the step response.  The time constant can be derived from the step response.  The inductor would be biased under different steady state operating conditions prior to the step.  Then you could use a PLECS Simulation script to iterate over a range of operating points, per the script in the attached model.