Speed sensorless vector control of a redundant permanent magnet wind power generator

Permanent magnet motors are coming more and more popular in many low speed and high speed applications. The conventional motor drive, consisting of a standard speed induction motor with a gearbox, can be replaced of a very low speed or a very high speed permanent magnet motor having no gearbox. The advantages are, for example, the increased efficiency and the reliability, and the reduced weight, noise and costs of the whole drive system. Permanent magnet motors can be designed efficiently for very low speeds with a high pole number. This makes PM-machines very attractive for wind power generators, which are in high power (> 1 MW) wind mills typically rotating about 10 rpm - 20 rpm. One important aspect of motor drives is the reliability of the drive system. The reliability of the PM wind power generator can be increased by using multiple stator modules or stator segments independent of each other. These segments can be considered, for example, as independent stator parallel windings which are each fed by own frequency converter. If one of the frequency converters fails, the other ones can continue the operation while the failed unit is changed. This paper describes the speed sensorless vector control of a variable speed multi-module PM wind power generator. The theory and laboratory tests are shown for a 4x1 kW PM-generator. Finally, the actual wind power generator tested is a 16 rpm 3 MW. axial flux PM-generator consisting of 3 stator modules.