# How to use variable inductor?

684 views
I am working for inverter with RL load. I want to check the  system under differnt load variation. Is it possible to add variable inductor availabe in library. It requires two input, could you help in this regards?
asked Jul 13, 2022

+1 vote

The voltage across a variable inductor is determined by: v = L*di/dt + i*dL/dt.  This arises from application of the chain rule for d(L(t)*i(t))/dt.  Therefore you need two inputs into the variable inductor component to describe its behavior.  Those correspond to the two inputs of the variable inductor block.

The first input is the L(t) and the second input dL(t)/dt.  If you have a three phase inverter (without mutual coupling between the phases) then the input to the block should be [L1,L2,L3,dL1/dt,dL2/dt,dL3/dt].

That being said, do you have a particular application in mind or way  you want to model the variable inductor?

At first glance it sounds like you simply want to step through various fixed inductance operating points. Note that stepping through inductance values without defining dL/dt is unrealistic from a physical perspective.  Another way of thinking about this is conservation of energy, where the energy stored in an inductor is E=1/2*L*i^2.  Applying a step change in inductance is a step change in stored energy.  Where does that energy come from?  The dL/dt term ensures energy is conserved.
answered Jul 15, 2022 by (1,941 points)
selected Jul 18, 2022 by karthik
Thanks Bryan