Three-phase Asymmetrical Harmonic Detection Circuit

In the past years, electrical harmonic pollution is getting more and more serious with the wide use of power electronic devices. And it is very harmful to the quality of power energy. Harmonics detection becomes an important branch of harmonic studies and a main basis of harmonic analysis.This dissertation pointed out some problems in existing harmonics detection used in three-phase unbalanced system by investigating and studying different kinds of harmonics detection methods. Many typical three-phase unbalanced circuits is described and analyzed in the dissertation. A new type of harmonic detection method was employed in three-phase unbalanced circuits, which combined symmetry component and rotation transform theory. Because it was very important to filter out DC component, a further investigation was given to the concept of lowest filter frequency used in AC components after rotation transform. The lowest filter frequencies were obtained for ordinary signals in power system. A clear explanation was put forward for the principle of selecting order and cut-off frequency in low-pass filter.In chapter 3, a harmonic detection method based on rotation transform theory was discussed and deduced theoretically. The method overcomes some defects existing in the methods based on instantaneous reactive power theory. It can detect both positive-sequence and negative-sequence components of arbitrary order harmonics through clockwise rotating coordinate and rotating anticlockwise transformation. In addition, the extraction of zero-sequence components in arbitrary order harmonics is gained through stiffly theoretical deduction. This method can be used not only in the detection of arbitrary order harmonics in 3-phase 3-wire unbalanced circuits, but also in 3-phase 4-wire system. Since the required signal length for this method is shorter, the detection method was excellent in real-time performance.In chapter 4, various typical unbalanced circuits were simulated and analyzed in MATLAB/Simulink environment. The figures and data gained from simulation proved that the detection method was correct and feasible. Furthermore, the effects caused by power wave...