An Improved Parameter-free Waveform Controller for Fast and Accurate Measurement of the Magnetic Properties of Grain-oriented Electrical Steels

To address nonlinearity-induced waveform distortion and slow convergence in the magnetic characterization of electrical steels, a parameter-free controller is proposed in this work, which enhances convergence speed while maintaining tracking accuracy and avoiding parameter dependence via adaptive compensation mechanisms. The controller consists of two primary components: the first incorporates polynomial fitting for rapid evaluation, which considerably reduces the number of iterations; the second employs a strategy that decouples frequency-domain and time-domain control. This strategy initially normalizes the waveform, then independently modulates its amplitude and shape, thus enabling rapid and precise waveform control. The controller has been successfully implemented in three one-dimensional (1-D) magnetic measurement systems. The results demonstrate that through assessment of the initial excitation in magnetic measurements of grain-oriented silicon steel, the initial waveform error is reduced to less than 3%, the harmonic content of the final waveform is controlled to approximately 0.2%, and the root mean square error of the waveform is maintained below 0.5%. Furthermore, magnetic property measurements were conducted over a frequency range from 2 Hz to 2000 Hz, with multiple loss values obtained at different frequencies for uncertainty analysis.