An Improved Phase Locked Loop Detection Method based on a Novel Dual Second-order Generalized Integrator under Unbalanced Grid Conditions

Aiming at the problems of grid frequency oscillation and phase distortion in the traditional synchronous reference frame phase-locked loop(SRF-PLL) method for detecting three-phase asymmetric power grid fault signals, an improved PLL method based on a novel dual second-order generalized integratoris proposed. The fundamental voltage component and its 90 degree phase shift component can be extracted by using the novel dual second-order generalized integrator (DSOGI), and then the two orthogonal voltage components are generated. Through the positive sequence calculator (pSC), the positive sequence voltage component is obtained and the disturbance influence caused by the negative sequence component can also be avoided. Meanwhile, in order to eliminate the AC component of the positive voltage component, the low pass filter (LPF) module is used before the positive sequence voltage component enters the phase locked loop (PLL) module. Through simulation and experimental verification, the proposed improved PLL detection method based on the novel DSOGI has proven to perform better than the traditional SRF-PLL both for rapidity and accuracy on detecting the frequency and phase of unbalanced power grid.