The fourth order flux observer with in-loop filter for permanent magnet synchronous motor sensorless control

Abstract

Given the presence of various non-ideal conditions, such as detection errors, converter non-linearity, noise, and parameter mismatches, the flux model experiences the introduction of DC bias and high-frequency harmonics, which subsequently deteriorate the accuracy of flux estimation. To dispose these issues, an improved non-linear flux observer (FOIFFO) using a second-order generalised integrator as an in-loop filter is proposed for the sensorless control of permanent magnet synchronous motors. The observer demonstrates robust performance in eliminating DC bias and having a strong filtering ability for high-order harmonics even without amplitude and phase compensation to accurately estimate the rotational speed and rotor position. The performance of the method is analysed by transfer functions and bode plots, while the discretisation method of the FOIFFO is proposed. Finally, the new sensorless control strategy is verified by synthesising the experimental results.