An Integral Method to Improve PLL Performance under Unbalanced Electric Grid Conditions

Abstract

Accurate phase information on three-phase grid voltage and currents which are supplied by PLL are needed in power system operation. Conventional three-phase synchronous reference frame-based phase locked loop is generally sufficient during balanced operation conditions. But unbalanced in input signal set causes a double-frequency ripple. The output signal is not ideal. There are lots of improved SRF-PLL methods, aiming at removing the double-frequency ripple such as DSC-PLL,MAF-PLL, but these methods may causes a certain time delay. DIF-PLL method is based on adding another signal, which has reverse polarity ripple. It may amplify the harmonic signal. In this paper, an INT-PLL method based on integral is proposed, which wont amplify the harmonics. The comparison of these methods and simulation results are given in this paper.