A robust PLL for grid interactive voltage source converters

Phase locked loop (PLL) is an important part of the current-controlled grid-connected converter. Its job is to estimate the phase angle of the grid voltage. If the PLL is not robust, the grid-voltage distortion will lead to an error in the estimated phase leading to a degradable performance of the converter. In this paper, the effect of the PLL on the operation of a current-controlled voltage-source converter is examined. A PLL synthesis is proposed, to track the phase angle of the distorted grid voltage, and compared with a previously investigated PLL. The result found is that the proposed synthesis of the PLL is superior in case of grid voltage harmonics other than the 5^th and the 7^th orders. Moreover, the voltage amplitude oscillation has been reduced from 8% to 3%, with the proposed PLL, compared to 5% with the previously investigated PLL.