Modeling and Simulation of Phase-locked Loop for Grid Voltage Based on the Improved Synchronous Reference Frame

Aiming at the problem that the traditional phase-locked method can not accurately detect the phase and frequency of the grid voltage with the unbalanced three-phase power grid, the improved phase- locked loop of the synchronous coordinate system based on multivariable filter is proposed. By using the multivariable filter to extract the positive sequence components of the fundamental voltage, the disturbance of the negative-sequence voltage components to the detection result of the PLL can be avoided. At the same time, the feed forward frequency estimation module is added in the PLL structure, which can estimate the frequency of the input voltage signal and quickly eliminate the frequency error to make the phase locking time of PLL significantly be shorter. The low-pass filter is provided to filter out harmonics of the positive sequence components of the fundamental voltage. Furthermore, it is modeled and simulated. And the simulation shows that the proposed improved algorithm can accurately lock the voltage phase and detect the shift of the grid frequency with good accuracy and effectiveness.