Due to the SS-PMG consisting of two electromagnetically separated generating units, it can be also modeled as two independent decoupled machines. A per-phase equivalent circuit is shown in Fig. 3. The rotor winding is short-circuited and is mechanically connected to the turbine, and the stator terminals are connected to the grid. A voltage is induced in the stator
windings at grid frequency in the steady state, and in the shortcircuited slip rotor, a voltage is induced at slip frequency. In this circuit, the slip rotor is referred to the grid frequency, and
the slip speed is taken as positive in the generator mode. The modeling of the generator is done in the d-q reference frame that is fixed to the PM rotor, for both the grid-frequency and
slip-frequency generator components.