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The Study of the Digital Three-Phase Phase-Locked Loop in the Photovoltaic Grid System

In order to track the phase of the voltage of the grid quickly and accurately in the photovoltaic grid system, a digital three-phase phase locked loop optimization method that can be completed by FPGA, which can lock the in a short time and adjust the power system voltage phase to the synchronization with the grid voltage. This design consists of three-phase phase detector, comparator and bit phase locking circuit. The principle of synchronous rotating coordinate transformation and lookup table of RAM are used to adjust the phase error more and more fine-tune. The adjustment of the phase is controlled by the waveform output of driver without analog circuit, besides the ability of anti-jamming is improved by the full digital designation and the dynamic characteristics is better. The system is simulated with MATLAB/Simulink and the given results show that this method greatly shorten the time needed for adjusting the phase difference. Obviously the precision of the system has been improved and then the effectiveness of the proposed method was verified.