Direct determination of currents spectra of synchronous machines at load perturbations

Paper presents an iterative algorithm for direct determination of current spectra at a steady state of synchronous motors when some perturbations occur in a mechanical load torque. In such cases electromagnetic and mechanic phenomena are strongly related, what is reflected by disturbances in the angular velocity and in all motor currents. Non-linear character of equations describing such performances leads to essential difficulties of finding the steady-state solutions directly. The algorithm is presented by a case study of a synchronous motor loaded by a torque with an alternating component. It is assumed that in steady-state, a synchronous motor runs synchronously but periodic perturbations in the angular velocity appear. For such performance the steady-state is found by the harmonic balance method. The paper shows how to formulate the algorithm and presents the properties of measurable motor currents. It is just a first step in the study of disturbances of stator currents due to same faults in a mechanical part of a drive with synchronous motors.