Study On Phase-Locked Loop For Grid-Connected Converters

The phase-locked synchronization technology is a common question in the grid-connected converters, and also is a most basic question in the converter control system. The quality of the phase-locked loop affects directly the performance of the control loops in the connected converter. Under voltage unbalance and distortion, it is necessary to capture the phase of voltage positive-sequence fundamental component accurately. Moreover the signal frequency is N times than power net frequency and it is sampled in equal interval. The most effective way is usually using the phase-locked loop (PLL).In this article, the fundamental theory, the work status, the basic composition and mathematic phase model of PLL are discussed. Aiming at unbalanced and distorted voltage in power net, the phase detector algorithm based on d-q vector transformation is studied, which can eliminate fundamental negative-sequence voltage and harmonics. Obtained direct-current voltage component reflects phase error. Signal delay cancellation technology (DSC) is adopted to eliminate the negative-sequence. The parameter design method of PLL is obtained through establishing PLL transfer function.Based on the MATLAB simulation software, PLL dynamic simulation model is established. Parameters values are obtained and the algorithm is verified. The system based on digital signal processor (DSP) is developed. The hardware circuit and software system of experiment is achevied on TMS320LF2407EVM appraised panel. The experimental results show that the output signal can track the frequency and the phase of the power net voltage rapidly.