Hello, you could add a series-connected controllable voltage source whose value is determined by custom logic calculations (perhaps via a lookup table) that you define. But if you just want the value of Vf to change based on the system parameters and not dynamically during a simulation, I recommend that you assign a variable to the block parameter and use the initialization commands to define your variables and calculate what the value of Vf should be, rather than provide an actual numerical value each time. Let me know if that's not clear.
