Active reduction of magnetic noise in asynchronous machine controlled by stator current harmonics

Asynchronous machine magnetic noise is essentially composed of spectrum lines of which the frequencies are directly tied to the rotation velocity of the rotor. In order to suppress some magnetic noise components, it is possible to inject into the stator, current harmonics of which the magnitudes and phases can be controlled and of which the frequencies are linked to the rotation speed. The prototypes realised in the laboratory extract the rotation frequency information from a mechanical coder. As the information about the speed is also contained in the stator currents, it is possible to use this property in order to lead to a magnetic noise active reduction independently of the constraints imposed by the mechanical link between shaft and coder. This active reduction method is outlined and the results on a 15 kW 4 pole machine are discussed.