A harmonic current detecting method for three-phase unbalanced systems

This paper proposes a novel harmonic detection method for three-phase unbalanced systems. The new method can be used to detect the positive, negative and zero sequence components of any term of harmonic currents respectively. The detection method for both balanced and unbalanced three-phase power systems are discussed in detail. In an unbalanced system with zero-sequence, the three-phase currents are transformed to the generalized dk-qk coordinate firstly, and then processed to low pass filter and inverse coordinate transformation in turn to obtain the positive sequence component. Only by changing the phase sequence from a-b-c to a-c-b, the negative component can be detected similarly. Meanwhile, the zero-sequence component is decomposed to p and q components then filtered by low pass filter respectively. Finally, the three components are summed up to obtain the detection result. The simulation and experimental results show that this method is valid for detecting any term of harmonic current with high precision nevertheless the distortion and unbalance of three-phase systems. It can also be used to detect the fundamental active and reactive power. (4 pages)