PMG technology has long been used in the small exciter motors for large synchronous generators, which are the mainstay of conventional power generation. Other PMG applications include their use in cable winding machines for the mining industry.
For PMG manufacturers, the wind industry's large high torque machines are a challenge. Global power industry giant ABB has been among the first to produce PMGs for the wind industry and a Canadian company, TM4, has developed a PMG design for an up to 750 kW wind turbine and is seeking a wind turbine partner to develop a 3 MW design. The Switch, a Finnish company, designs PMGs and converters for the wind industry and has clients who buy either or both for direct drive systems.
A few PMGs have been designed using the most common ferrite magnets, but most new PMG designs now employ a much more powerful rare-earth magnet with higher magnetic flux, the neodymium-iron-boron magnet. It is the supply from China of comparatively cheap magnets of this type that has stimulated their use. The principal expensive ingredient is the rare-earth element neodymium, found mainly in China and Mongolia.
The Chinese have developed their own industry to exploit their indigeous resource, with dramatic price cuts resulting, from typically EUR 160/kg in the mid 1990s to EUR 16/kg in 2006. According to the best traditions of supply and demand, the price has subsequently increased to a current value around EUR 30/kg. There has been some concern about a Chinese stranglehold on this market. Several companies, however, have expressed confidence that the rare earth materials are by no means really rare in world supply and that other supplies can readily be opened up if it proves necessary.
