Fast Digital Feedback Algorithm for Efficient Control of Magnetic Flux Density Waveforms

An advanced digital feedback algorithm providing defined waveform shapes of magnetic flux density (as well as induced voltage) is demonstrated. The algorithm is based on the iterative process predicting the exciting field waveform to be used in order to achieve the desired waveform of the voltage induced in the secondary winding along with the use of advanced hardware configuration utilizing appropriate exciting power amplifier (AMP) acting as a voltage-to-current converter. An approach based on the inverse function computation [inverse function digital feedback (IFDF)] applied to the response of the sample under test (SUT) to the initial exciting field waveform was used to estimate the exciting field that should be applied to magnetize the sample. SUT is usually made of ferromagnetic/ferrimagnetic material, thus constituting basically a nonlinear hysteretic system. Due to the nonlinearity and hysteresis, the iterations have to be repeated more times until the differences between actual and ideal waveforms fit into the required limits based on the chosen criteria, such as form factor (FF), total harmonic distortion (THD), and sample Pearson’s correlation coefficient (
r_xy
). The effectiveness of the algorithm is subjected to testing on various magnetic materials in a wide range of frequencies and amplitudes of the exciting field/flux density in order to judge its robustness and stability as well as the number of iterations steps (or time) needed to obtain the satisfactory waveform shape.