Identifying the Rotor Flux-Oriented dq-Axes of an Induction Machine within a Time-Stepping Finite Element Analysis

Abstract:
Drive controllers of three-phase AC machines usually make use of the dq-system for control variables. For fieldoriented controlled induction machines (IMs), aligning the d-axis with the rotor flux has proven to be a particularly practical definition. However, when it comes to the electromagnetic design process of an IM utilizing the time-stepping finite element analysis (FEA), the dq-system is not a suitable tool for the electrical input variables. This is because the flux-fixed dq-axes of the IM are unknown at the beginning of the simulation. Nevertheless, in order to facilitate communication between control engineers and electromagnetic design engineers, it is desirable to evaluate the simulation results in the dq reference frame. This paper describes a method to identify the circumferential position of the rotor flux and thus the d-axis, allowing the transformation of the stator currents into the dq-system. The presented method is validated against measurements.