Robust H∞ Active Damping Filter With Preserved Resonant Peak for Resonant Harmonic Suppression

Filter-based active damping (AD) without additional sensors has been widely used in LCL-type grid-tied inverters. For the resonance problem of the LCL filter, the AD filter is devised through the application of the amplitude shaping and/or phase shaping according to the Nyquist stability criterion. Although many robust AD filters have been studied, there is no attention paid to whether the harmonic content near the resonant frequency meets the grid standards. Besides, the impact of the resonant peak introduced by the LCL filter on grid-tied inverters with an AD filter is unclear. Therefore, in order to explore the role of the LCL filter’s resonant peak, several AD filters are discussed in detail in this article, and the robust
$H_{\infty }$
AD filter with preserved resonant peak is proposed. The proposed filter is realized by selecting the suitable sensitivity weight function in
$H_{\infty }$
control. The design procedure, selection of weight functions, and stability robustness analysis of the AD filters are presented. Finally, the experimental results give the total harmonic content of the grid current and the harmonic content near the resonant peak to validate the effectiveness, robustness, and resonant peak effect of the proposed filter.