Abstract
Phase-locked loop (PLL) is a key technology in grid connected converters. It is also a most basic technique in the grid connected inverter control system. The performance of the phase locking synchronous circuit will directly influence the technical function and operation stability of the grid connected converter. The phase angle and the frequency of the grid voltage are the most basic information in the grid connected converter. Tracing this information accurately and rapidly is the guarantee of the stable operation of grid connected inverter control systems. Under the condition that voltage distortion and unbalance phenomenon becomes more and more serious, the task of grid connected converters synchronous is to correctly detect the grid voltage signal. Usually the most effective way is to use phase-locked-loop.