Influence of rotor current on noise excitation in electrically-excited synchronous machines

In this paper, the influence of rotor current on the noise excitation in electrically excited synchronous machines is analyzed. For this purpose, the air gap flux density is calculated throughout the machine operating range and used to calculate the radial and tangential pressures on one representative stator tooth. The rotor flux linkage interacts with the stator flux-linkage in d-axis, enabling influence on air gap flux density and pressure harmonic content and amplitude. Finally, a characteristic operating point of torque and rotational speed is chosen for which all possible current combinations are determined, and compared in their resulting noise-exciting pressures. Using different criteria, three optimal current combinations for the operating point are determined, and the resulting trade-off between machine efficiency and reduced noise excitation analyzed. It is shown that while reducing efficiency, the method may be used for avoiding machine resonances at select operating points.