Improved MSTOGI-PLL with enhanced control under non-ideal grid voltage conditions

Abstract

Integration structure of second- and third-order generalized integrator phase-locking loop (MSTOGI-PLL) has received attention for the processing ability of harmonics and DC bias contained in grid voltage. However, due to that MSTOGI-PLL is sensitive to interharmonics and subharmonics, once low order harmonics dominate, the narrow bandwidth will result in slow response. Hence, based on the analysis on input and output frequency characteristics of existing MSTOGI, a frequency gain structure within the MSTOGI structure is added to improve the suppression ability, either to low-frequency or high-frequency harmonics. Secondly, in order to accelerate response and reduce overshoot of the output frequency of the phase-locked loop (PLL), a nonlinear PI dynamic regulator based on a hyperbolic threshold function is constructed. Furthermore, from the perspectives of voltage phase and frequency tracking error indicators, by comparing with three other types of PLL structures in weak grid application, the effectiveness of the proposed method is verified through simulation cases. Finally, a physical hardware platform based on dSPACE1104 is built to extract the grid voltage from the three-phase voltage regulating transformer, the theoretical derivation and simulation results are verified. The phase deviation is controlled within 0.44 rad s-1, and frequency deviation is controlled within 0.07 Hz.