Application of the Principles of Field-Oriented Control for the Measurement and Metrological Characterization of Soft-Magnetic Steel at Rotating Magnetization

Modeling the behavior of soft magnetic materials used in electrical machines relies on suitable measurements which are able to determine magnetic properties under conditions similar to those occurring in electrical machines. One example for such conditions is to generate a rotating magnetization and apply mechanical stress to the sample material during the measurement. The behavior of the magnetic circuit for such measurements is strongly influenced by the nonlinear magnetic properties of the sample and its shape. To overcome these difficulties, a control strategy is developed by applying the principles of field-oriented control known from electrical machines.
The dynamic interaction between excitation and measured voltage is analyzed and a transient simulation model is implemented. The basic control problem is formulated in field-oriented equations. Then, the influence of nonlinearities on the control problem is examined. Based on the results of this analysis, a field-oriented control strategy capable of sufficiently suppressing unwanted flux density harmonics is derived. A modified coordinate transformation between physical and field-oriented quantities is introduced. It is shown that the modified transformation principle can map any rotating flux density distribution with periodically changing amplitude to the circular case. Therefore, the control strategy can be used to generate a wide variety of flux density distributions without changing the basic control structure. The control strategy is applied to a rotational single sheet tester capable of generating two-dimensional mechanical stress inside the sample. The functionality of the developed control is validated. The influence of different mechanical stress combinations on the measurement results is shown.