Three-Phase Grid Voltage Synchronization Using Composite Filters

For the application of three-phase grid-connected systems, the performance of grid voltage synchronization is crucial. Although some traditional grid voltage synchronization methods have good harmonic rejection capability and high precision, the transition detection time of the traditional grid voltage synchronization is not satisfied when considering the common grid faults such as symmetrical and asymmetrical voltage dips. In order to achieve the fast detection for voltage dips, this paper proposes a novel grid voltage synchronization method. It uses two low-order complex finite impulse response filters (FIR) to eliminate dominant low-order harmonics and separate the fundamental components respectively, and applies three second-order Kalman filters to estimate the fundamental frequency, positive-sequence and negative-sequence components respectively. Having the low-sampling rate and low-order structure, the proposed method has the high precision but faster detection response for voltage dips. And the experimental results show that the proposed grid voltage synchronization technique is easy to implement and has advantages regarding stability, rapidity, accuracy and the rejection of the harmonics.