Discrete-Time Frequency-Domain Disturbance Observer to Mitigate Harmonic Current in PMSM Drives and the Implementation With Reduced Delay

The disturbance observer (DOB) can be employed in electric drives to improve disturbance rejection. The
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-filter of classical frequency-domain DOBs to attenuate multiple harmonic disturbances is high order and faces issues, including discretization, numerical precision, and frequency adaption; thus, its realization in variable-speed drives would be challengeable. This article proposes a discrete-time multifrequency DOB (MFDOB) to address these issues. The
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-filter of the proposed design is constructed with an integrator and several parallel resonators in a closed-loop structure. It uses a single parameter per harmonic to control the disturbance rejection bandwidth and the performance is guaranteed under various fundamental frequencies. The impact of the computation delay on the MFDOB-based current control is studied, and the system with less computation delay exhibits a higher stability margin and a wider range of low sensitivity. To eliminate the computation delay, a real-time pulsewidth-modulation update scheme is also developed for the DOB-based two-degree-of-freedom controller. The proposed method is evaluated on a laboratory permanent magnet synchronous machine platform.