Two-Stages Sliding Fourier Transform

Two-Stages Sliding Fourier Transform for High-Performance Phase Angle and Frequency Tracking

Sliding Discrete Fourier Transform (SDFT) is computationally very efficient and it is able to provide excellent harmonic rejection when working at its nominal frequency. However, at the off-nominal frequency, both magnitude and phase angle contain errors due to spectral leakage. Moreover, its harmonic rejection ability is greatly impaired in this case. This algorithm presents a method to apply Sliding Fourier Transform under off-nominal frequency at a fixed sampling rate while maintaining its superior performance. This method involves the use of two stages Sliding Fourier Transforms (SFT). An SFT with fixed window width in the first stage is used to drive a variable window width SFT in the second stage.
The proposed technique (SFT-SFT) has been tested in real-time on dSPACE MicrolabBox using pre-generated voltage vectors to simulate the most inconvenient grid conditions. The testing scenarios proved its superior performance compared to the decoupled stationary reference frame PLL method.
The Simulink file provided here contains the implementation of the algorithm and the implementation of the decoupled stationary reference frame PLL for the sake of comparing their performance against the same inconvenient inputs