Interaction of induction machines fundamental wave design and asymmetries in the transient electrical behavior caused by saturation

In today´s AC machine drives the control is realized by considering the fundamental wave behavior of the machine only. However, the exploitation of the high frequency or transient properties of the machine can advantageously be used to obtain additional information on the state variables of the machine like flux or rotor position or detection of possible fault conditions. Especially for the estimation of the flux or rotor position in induction machines the practical performance of the resulting control is strongly influenced by the lamination design. Modern design tools for induction machines only consider the fundamental wave and only few effort has been made until now to investigate the interaction of the fundamental wave design and the transient electrical behavior. This work is focused on these interactions. A transient simulation of the machine based on a magnetic equivalent circuit model including lamination material hysteresis is applied to ascertain the connection between saturated areas in the lamination material and the signals obtained from the evaluation of the machines transient electrical step response. To verify this connection as well as to quantify the influence measurements were performed on different machines with specific lamination design each concentrated on dominant saturation in a different area like tooth or yoke in the stator as well as in the rotor. A comparison of the simulation and measurement results of the machines at varying flux and load levels is given and the reasons for the difference in the transient signals is discussed taking the fundamental wave as well as the transient field distribution into account. Based on these results a model of the interaction of fundamental wave saturation and the transient control signals is established where the asymmetries caused by saturation at the different areas of the lamination are each represented by individual phasors. Adding up the phasors of all areas leads to the resulting asymmetry of the machine and gives its dependence on the point of operation.