Stability analysis and concept extension of harmonic decoupling network for the three-phase grid synchronization systems

The harmonic decoupling network (HDN) structure has been widely used as prefilters in grid synchronization techniques, which can accurately extract the fundamental positive- and negative-sequence components and interested harmonics in unbalanced and distorted grid voltages. However, the stability of general HDN is seldom discussed. In this paper, the transfer function expression of general HDN is educed and its stability is proved by the root locus method. Also, it is found that HDN is a multiple-order complex vector filter (MOCVF) in essence. To extend the concept of HDN, the generalized MOCVF (GMOCVF) is proposed. Moreover, an optimized solution to the pole assignment of GMOCVF is presented. As a sequence, GMOCVF can be easily designed to achieve faster dynamic response or better harmonic attenuation compared with HDN under equivalent conditions. In the end, the effectiveness of GMOCVF and the performance comparison between HDN and GMOCVF are verified by the simulation and experimental results.