On the spatial propagation of transient magnetic fields in AC machines

AC motors have proliferated as the most important machine type used in variable speed drive systems. The dynamic analysis and description of revolving field machines is supported by well-established theories: Park´s transformation (1929), and the space vector theory by Kovacs and Racz (1959). Yet some inconsistencies with the theory of dynamic systems exist. First, the machine eigenvalues suggest the existence of two damped oscillators. Second, it appears unsatisfactory that the respective eigenfrequencies change with the velocity of the reference frame. This contradicts the common understanding according to which the eigenfrequency is an inherent system property. A clarification is reached using a novel approach for dynamic AC machine analysis. The approach is based on complex state variables. It permits relating a transient condition to the propagation processes in the space of distributed magnetic fields. The formal analysis constitutes an extension to the space vector theory and to the theory of dynamic systems