Permanent Magnet Synchronous Generator

A permanent magnet synchronous generator, or PMG, is an electric generator whose magnetic excitation field comes from a permanent magnet mounted on the rotor rather than from an externally powered coil, so the stationary stator windings generate current as the magnet turns past them. Because the rotor and its magnetic field always turn at the same speed, the frequency of the electricity produced depends directly on rotation speed, and three sets of stator conductors spaced 120 degrees apart create a rotating magnetic field that stays locked in step with the spinning magnet. Needing no separate DC excitation supply or brushes lowers maintenance, though the air gap magnetic flux cannot be adjusted, which makes voltage regulation harder since output voltage rises and falls directly with shaft speed. This type of generator is credited as supplying the majority of the world commercial electrical energy, converting mechanical power from steam turbines, gas turbines, reciprocating engines and hydro turbines into grid electricity, and some wind turbine designs use it as well.