The PMG is proposed as a wind turbine generator due to its property of self-excitation. The stator winding is connected to the load, and is insulated. The rotor is provided with a permanent magnet pole system, which is resistant to the effects of possible dirt ingress. However, the permanent magnets will attract ferromagnetic swarf. They also call for special care when assembling, to avoid damage and accidents to personnel. Maintenance is generally restricted to bearing lubrication only. A major problem is the necessity of maintaining the rotor temperature below the maximum operating temperature of the magnet, which may be limited by the Curie point of the magnetic material, and also by the thermal properties of the binding material in the case of powder metallurgy composites.
Large machines are reported (17 MW motors), but most research papers describing generators consider machines with ratings less than 10 kW. The synchronous nature of the operation causes problems of start, synchronisation, and voltage regulation.
Methods of control include full power frequency inverter, and cyclo-converter. Methods of improving voltage regulation include the application of full voltage, large capacitance capacitors.
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