Active reduction of audible noise exciting radial force-density waves in induction motors

This paper presents an approach to the active reduction of radial force-density waves. Additional flux-density waves are generated by the injection of additional and particular low-power current harmonics. With these flux-density waves a force-density countershaft to an acoustic annoying radial force density wave is generated. In this contribution a mathematical model to estimate the amplitude, frequency and phase shift of the required current harmonic is presented. The prediction of the phase-shift is strongly dependent on saturation effects and on the interaction of the additionally imposed and existing flux-density waves. Therefore, a finite element (FE) experiment set is proposed to increase the accuracy of the analytically predicted phase angle. The active injection of force-density countershafts is performed, analyzed and evaluated. The assessment is performed based on FE simulations. The authors found that the injection of force-density countershafts is applicable for force-density waves with any circumferential oscillation modes and frequency in general. However, the consideration of oscillation modes is limited to r = 0, ±2p, ±3p and ±4p in order to keep the additional losses in the machine within an acceptable limit. The proposed approach is robust concerning the accuracy of the phase shift of the additionally imposed current harmonic.