A Novel Time-Delay Filter Implementation for Resilient Control of Active Power Filters

The increasing penetration of power electronics-based devices has led to reduced power quality in power grids, making effective solutions like active power filters (APFs) essential. To tackle this problem, this article proposes a novel time-delay filter aimed at improving the accuracy of reference current generation (RCG) and enhancing the overall compensation performance of APFs. The proposed filter is implemented as a dual cascaded second-order time-delay (DCSOTD) filter and exhibits exceptional harmonic rejection capabilities and stability properties. It inherently rejects the negative sequence component of an unbalanced and distorted load current, along with the $5^{th}$ negative and $7^{th}$ positive sequence harmonics. More so, the proposed DCSOTD filter offers two additional design degrees of freedom, enabling the selective rejection of any two harmonic components of the load current and their odd integer multiples. Its delay-independent stability feature makes it well-suited for APF applications that involve a wide range of frequency variations. Comparative performance analysis with DSOGI and DROGI-based RCGs underscores the superior performance of the proposed DCSOTD filter in enhancing power quality, particularly under unbalanced voltage and load conditions. Additionally, its stability is demonstrated in a more electric aircraft grid during a significant frequency variation from 400 Hz to 800 Hz.