A Cascaded Integral Action Based Filter for Distorted Conditions

This article proposes a cascaded integral action-based filter by relying on the orthogonal output of a T/4 delay block. The proposed filter employs an integrator together with mechanisms involving feedback of the filtered signal and feedforward of its orthogonal input. Based on this approach, the proposed filter addresses the problem of initial state when applying a direct integral action to a sinusoidal voltage. More so, the proposed filter provides notch filtering characteristics at certain harmonic frequencies, thereby achieving improved harmonic rejection in comparison to existing second-order generalized integrator filter. Without frequency adaptivity, the proposed filter achieves fast response, and more importantly, provides excellent filtering of harmonic components at off-nominal frequencies of the supply voltage. Furthermore, dc-offset rejection in the proposed filter is considered together with its FLL implementation for frequency, phase angle, and amplitude estimations. Linearized model and stability evaluation of the proposed filter's FLL are presented while detailed analytical, simulation, and experimental validation of the proposed filter's performance for applications involving voltage parameter estimation for synchronization purposes and reference signal generation are provided. Results obtained demonstrate superiority of the proposed filter in terms of harmonic rejection and estimation speed when compared to existing filtering techniques.