1201 apart in space, shown in Fig. 4. This stator winding either
exports AC power (synchronous generator) or imports AC power
(synchronous motor) and the rotor always energized by the DC
supply. Depending upon their construction, the synchronous
machines are of two types salient pole and cylindrical pole. The
salient pole type is a slow speed machine, mainly employed in
HEES. The cylindrical pole type is a high-speed machine that used
in high-speed application [147].
The doubly fed induction machine consists of a stator with
three-phase AC winding, Rs, Ys and Bs, distributed 1201 apart in
space, shown in Fig. 5. This winding either exports AC power
(generation) or imports AC power (motoring). The rotor of doubly
fed induction machine is energized by AC supply, which contains
a three-phase distributed winding with the same number of poles
as the stator and displaced by angle θ. This winding is usually
star connected with the ends of the winding brought out to three
slip rings, enabling external circuits to rotor for control purpose
[147].