The acoustic impact of rotor eccentricity in switched reluctance machines

The cost-efficient switched reluctance machine is highly appealing to the automotive industry. In this application acoustic noise is a crucial criterion, which is usually addressed during the design process. However, parasitic effects, such as rotor eccentricity, are normally not a design target but only a finding during the test of the prototype. This paper deduces a theory that mathematically describes the effect of static and rotating eccentricity. A 2D Fourier series in space and time was used to investigate the impact of an asymmetric force excitation. The theory was verified by means of a measured spectrogram of a small laboratory machine. Afterwards, the theory was applied to investigate the acoustic behavior of an automotive-size switched reluctance machine with rotor eccentricity. The theory proved effective and is ready-to-use to foresee potential acoustic problems already during the design of future switched reluctance machines.