Detecting positive-sequence component in active power filter under distorted grid voltage

In distribution power system, an active power filter (APF) is installed at the point of common coupling (PCC) bus to eliminate harmonic currents injected by non-linear loads. The active power filter, therefore, needs to synchronize with the grid by employing a second-order-generalized-integrator frequency-locked loop (SOGI-FLL) to detect the positive-sequence voltage component. If the grid is highly distorted by harmonic currents, it degrades the accuracy of SOGI-FLL estimation and the APF cannot get correct grid voltage characteristics. This paper introduces a new grid synchronization structure based on the SOGI-FLL under distorted voltage condition. The proposed structure behaves as a high-order filter to completely remove harmonic components and inherits advantages from SOGI-FLL. The grid voltage magnitude and frequency, thus, are detected precisely under distorted grid. Simulation results are presented to verify the proposed system performances.