Think of it as a rotating transformer, with the primary windings residing in a stationary casing (stator) and the secondary conductors attached to an inner shaft (rotor).
The modelling inaccuracy and parameter drift in motor control, such as the stator and rotor resistance shift with temperature, act as the disturbance in the control system.
Tesla's invention is, in essence, a rotating transformer. Its primary windings reside in a stationary steel casing (the stator) and and secondary conductors are attached to an inner shaft (the rotor).
