Phase locking system for three-phase alternating current electric grid and method thereof

摘要

A phase locking system for a three-phase alternating current (AC) electric grid and a method thereof are disclosed. The method includes: receiving a three-phase voltage of the AC electric grid and converting the three-phase voltage to a two-phase voltage signal, each of which including a positive and a negative sequence components; obtaining a pure positive sequence component by subtracting the negative sequence component from the voltage signal of each phase and using αβ/dq coordinate transformation and low-pass filtering, and phase locking the pure positive sequence component; and obtaining an error signal by subtracting a disturbance variable and subsequently subtracting the positive sequence component from the voltage signal of each phase, wherein the disturbance variable includes the negative sequence component, and obtaining a signal including the negative sequence component by performing a α-β/d-q coordinate transformation on the error signal and adjusting the error signal through a regulator.

主权项

1. A phase locking system for a three-phase alternating current (AC) electric grid, comprising:
an input module, for receiving three-phase voltages of the three-phase AC electric grid and converting the three-phase voltages to two-way voltages Vgridα and Vgridβ, each of which comprising a positive sequence component and a negative sequence component; a first separation module, for obtaining a positive sequence component dpos at a d-axis and a positive sequence component qpos at a q-axis by performing a coordinate transformation from a α-β coordinate system to a d-q coordinate system on a first variable to be separated, and next outputting positive sequence components Vαpos and Vβpos corresponding to the voltage of each way by performing the coordinate transformation from the d-q coordinate system to the α-β coordinate system on the positive sequence component dpos at the d-axis; and a second separation module, for outputting negative sequence components Vαneg and Vβneg corresponding to the voltage of each way by performing the coordinate transformation from the α-β coordinate system to the d-q coordinate system and then the coordinate transformation from the d-q coordinate system to the α-β coordinate system on a second variable to be separated; wherein the first separation module and the second separation module are coupled as a closed loop feedback, the second separation module obtains the negative sequence component by adopting a closed loop compensation, and eliminates an error in the first separation module, making the first separation module separate out the positive sequence component for phase locking.