The difference between asynchronous generators and synchronous generators:
They can all be used in variable speed fans, provided that appropriate converters are selected.
Asynchronous generators can be further classified according to their rotor structure as follows:
(a) Squirrel-cage induction generator – The rotor is squirrel-cage. Due to its simple and reliable structure, low cost, and ease of grid connection, it is widely used in small and medium-sized generator sets;
(b) Wound-rotor doubly-fed asynchronous generator – The rotor is wound. The stator is directly connected to the power grid to transmit electrical energy, while the wound-rotor is also controlled by a frequency converter to transmit active or reactive power to the power grid.
Synchronous generators can be further classified according to the type of magnetic poles that generate the rotating magnetic field:
(a) Electrically excited synchronous generator - the rotor is a wire-wound salient pole type magnetic pole, and the magnetic field is generated by external DC current excitation.
(b) Permanent magnet synchronous generator - The rotor is made of permanent magnet poles made of ferrite material. It is usually a low-speed multi-pole type. It does not require external excitation, which simplifies the generator structure and thus has many advantages.
