A modified SRF-PLL for phase and frequency measurement of single-phase systems

In this work, a single phase phase-locked-loop (PLL) that uses a low-pass notch filter is proposed. The new PLL was derived from the synchronous reference frame PLL (SRF-PLL) in which the dq axis components were generated using the αβ reference signals. The single-phase grid voltage was used as the α component, whereas the αβ component was derived by delaying the grid voltage by 90° in phase. The dynamics of the proposed PLL were compared to those of the SRF-PLL. The frequency measurement using the new PLL showed better performance over the SRF-PLL and a second-order generalized integrator (SOGI) PLL. The proposed PLL displayed better performance under both variable frequency and distorted grid voltage conditions. Experimental results were used to validate the dynamics obtained from the simulation results. The proposed method adds very little complexity to the conventional SRF-PLL.