Have a look at 
ConstantActuator and at 
PermeanceActuator for an explanation of both converter
models.
Simulation of the force-stroke characteristic of the PermeanceActuator with a constant current I=3A and a forced armature movement (similar to measurements in reality) shows the dependency of both force-generating permeances G_ma and G_mb as well as inductance L on armature position x. Simulate for 8 s and plot vs. armature position feedX.flange_b.s (same physical quantities together in a common diagram for comparison):
    feedX.flange_b.f            // force of permeance model (permeance of stator iron neglected in this model)
    comparisonWithFEA.y[1]      // force of FEA model with non-linear stator iron 1.0718
    comparisonWithFEA.y[2]      // force of FEA model with mu_rFe=const.=1000
    actuator.g_ma.G_m           // permeance G_ma
    actuator.g_mb.G_m           // permeance G_mb
    actuator.L                  // inductance of permeance model
    comparisonWithFEA.y[3]      // inductance of FEA model for comparison (mu_rFe=const.=1000).