Performance Comparison of PLL Techniques for Grid-Connected Inverters

Weak grids are characterised by low inertia, unbalanced voltage and background superimposed harmonics. Phase locked loops (PLLs) are one important key for the integration of power electronics converters with these weak grids. However, PLLs mainly rely on the grid voltage which are affected based on the characteristics of weak grid. This paper presents a performance evaluation of SRF, DDSRF and DSOGI-PLLs. The PLLs are simulated in Matlab environments under different case studies. The results shows that DSOGI-PLL and DDSRF-PLL give precise phase estimation when working under balanced and unbalanced grid voltage. During operation under background harmonics, DSOGI-PLL accurately estimates the voltage phase as compared to other PLLs. On the other hand, SRF performance is deteriorated under any change of grid voltage like unbalance and/or existing background harmonics.