Fundamental-Frequency Positive/Negative-Sequence Detection Under Unbalanced and Distorted Grid Voltage Conditions

The correct value of the fundamental frequency positive/negative-sequence voltage vector and synchronous angle are essential for the normal operation of grid-connected applications. The paper proposed a method to detect this information under unbalanced and distorted grid voltage conditions. By the use of moving average filter (MAF), the harmonics were filtered with the fundamental and orthogonal components detected. After this, the fundamental frequency positive/negative-sequence voltage vector and synchronous angle were calculated. Uniting the MAF with DSOGI-FLL and improving it, the method based on enhanced MAF-DSOGI-FLL was reached which improved the frequency tracing speed efficiently. Simulation and experimental results prove that the proposed method not only can detect the fundamental frequency positive/negative-sequence voltage vector and synchronous angle quickly and accurately, but also can track the frequency mutation rapidly.