Improving the Decoupled Double SRF PLL for grid connected power converters

One of the critical issues in control of grid connected power converters is synchronization with the utility voltage. Decoupled Double Synchronous Reference Frame Phase-Locked Loop (DDSRF-PLL) can detect positive and negative sequences of voltage under unbalanced conditions. However, its dynamic response is very sensitive to phase angle jumps in the voltage which results in large deviation in the estimated frequency. This paper investigates conventional DDSRF PLL and hybrid Decoupled Alfa Beta (DAB) PLL, and then proposes a new DDSRF PLL that outperforms two mentioned PLLs. The proposed PLL is a combination of DDSRF PLL and dual second-order generalized integrator (DSOGI) that estimates grid frequency with lesser overshoot than those of two other PLLs. The performance of the proposed PLL is verified by using time domain simulation studies in the DIgSILENT PowerFactory software environment.