Enhanced Single Phase Locked Loop for Grid-Connected Converter in Distribution Network

Distributed generations are becoming increasingly attractive to consumers and such as in the future, the governing grid-connection standards are demanding due to the large number of alternative distributed energy resource (DER) and the multifunction converter, such as supplying reactive power, improving power quality. Now the grid-connected performances are much greater emphasized on the robust synchronous technique, which requires the phase, the amplitude, and the frequency of the utility grid for the operation of the grid connected power conditioning equipments. In such application, a more accurate and faster Phase Locked Loop is necessary, but the existing PLLs are lack of better performances. This paper presents an improved single PLL for the grid-connected converter based on instantaneous DQ theory and nonlinear control in distribution network; the advantage of PLL includes high accuracy, independent frequency, and faster response. The validity of PLL is verified by simulation and experiment.