An Enhanced FAH-PLL-Based SAPF Control Method Under Distorted Grid Conditions and Sensor Failures

Abstract

The widespread use of power electronics-based converters and non-linear loads in modern power systems has induced an increase in harmonic distortion and power quality issues. In particular, DC-offset errors arising in current and voltage measurement systems can negatively affect the performance of phase-locked loop (PLL)-based synchronization algorithms, causing the generation of erroneous reference currents in shunt active power filter (SAPF) systems and a reduction in harmonic suppression performance. Conventional dq-based SAPF control methods, however, exhibit limited performance under grid conditions characterized by harmonics, unbalanced loads, and sensor-induced DC-offset errors. In this work, an improved dq control method based on a frequency adaptive hybrid-phase-locked loop (FAH-PLL) is proposed for three-phase SAPF applications. In the proposed method, the grid frequency and phase angle are obtained via the FAH-PLL structure, while the fundamental current components in the dq-axis are separated using a frequency adaptive hybrid (FAH)-based filtering structure. The FAH-PLL combines a second-order generalized integrator (SOGI), an all-pass filter (APF), and a positive-sequence calculator (PSC). This structure provides accurate and stable synchronization under harmonic distortion, grid-voltage unbalance, sensor-induced DC-offset errors, and frequency variations. The performance of the suggested control method is tested under conditions involving nonlinear loads, unbalanced loads, sensor-induced DC-offset failures, and grid frequency variations. The results obtained demonstrate that the suggested FAH-PLL-based method effectively suppresses harmonic components, significantly improves power quality, and reduces total harmonic distortion (THD) values below the limits specified in the IEEE 519-2022 standard. The results confirm that the suggested method offers an effective, stable, and reliable solution for SAPF applications under disruptive grid conditions and measurement errors.