Modeling and Simulation of Asymmetric Three-phase Grid Voltage Phase-locking Method Based on Improved Extended Kalman Filter

Under the asymmetric condition of the three-phase grid voltage, the traditional phase-locking method can not accurately and quickly lock the phase due to the existence of harmonics. To solve this problem, this paper proposes a three-phase grid voltage phase-locking method under asymmetric conditions. Based on the establishment of grid voltage fault model, the basic principle of the extended Kalman filter is given. In view of the problem that the signal cannot be quickly reacted to the abrupt signal during phase locking, the hysteresis comparator and the root mean square method are added to the extended Kalman filter. According to the two states of grid voltage balance sag and unbalanced sag, the simulation results and analysis of the extended Kalman filter and improved extended Kalman filter are given respectively. The results show that the improved algorithm can quickly and accurately realize the phase locking of the three-phase grid voltage under asymmetric conditions, and compensate the phase tracking error caused by various grid faults during the phase-locking process. It not only applies to ideal grid conditions, but also enables rapid detection of voltage signals under various asymmetric conditions such as voltage drop, three-phase unbalance and low-voltage harmonics, which can effectively compensate for the shortcomings of traditional methods.