Stability simulation and improvement of typical phase-locked loop of STATCOM with different equivalent grid R/L ratios

Abstract

Transient synchronization stability is the precondition for dynamic reactive power compensation of STATCOMs in the event of a grid fault, which might be so serious that their neighboring distributed power generators lose their synchronization stability. However, there are very limited research publication in this area. This paper focuses on STATCOM synchronization stability and its improvement. The proposed adaptive phase locked loop (PLL) is based on the estimated phase error rather than the estimated frequency error, which is an innovative approach not yet been seen in published papers. Moreover, the impacts of short-circuit ratio and the ratio of equivalent grid R to X are also investigated. Both steady-state analysis and time-domain simulation results are presented in this paper. The results show good consistency between steady-state analysis, simulation with a controlled current source model and with a detailed STATCOM model, and the differences are within reasonable range. Compared with the typical PLL, the proposed adaptive PLL demonstrates improved performance of transient synchronization stability.