How to model a variable RL branch?

Hi, I would like to implementing a current controlled variable RL branch using integrator. I have one using i(t) = integ( v(t) - i(t)*R ) / L, but this would develop an algebraic loop, which I want to avoid. Any ideas?

Answer 1

[Sebastian Castro]

This is the right approach, but as you said it does come with an algebraic loop. You can resolve this loop by adding in a Transfer Fcn block to act as a low-pass filter. In fact, several Simscape Power Systems blocks (e.g. PV Array) already do this under the hood.

The transfer function will typically take the form 1/(Ns+1) where N is associated with the time constant of the filter. You want to pick this value to be small enough that it doesn't filter out your system dynamics, but large enough that it doesn't slow down your simulation with high-frequency components.

Sebastian

[And Meng]

Hi Sebastian, I have added a transfer fcn with a time constant of (1e-6) after the divide sign. This return me an error message. I know that my fundamental frequency would be around 50 Hz, and not caring for other frequency components. Do you know what is causing this error?

An error occurred while running the simulation and the simulation was terminated
Derivative of state '1' in block 'xx/xxx/Subsystem/Integrator' at time 0.00495 is not finite. The simulation will be stopped. There may be a singularity in the solution.  If not, 
try reducing the step size (either by reducing the 
fixed step size or by tightening the error tolerances)