Improved EPLL performance using multiple sinusoidal signal integrators for grid-connected VSC system synchronisation

摘要

This paper presents a novel synchronisation technique, which is based on the structural modification of the conventional Enhanced Phase-Locked Loop (EPLL) by introducing Multiple Sinusoidal Signal Integrator (MSSI) modules. The proposed MSSI-EPLL proves to overcome the weakness of the EPLL by employing adaptive MSSI modules in both amplitude and frequency loops to effectively eliminate low order harmonics under distorted AC grid condition, without sacrificing the dynamic performance. The test bench setup also considers the application of a single-to-ground fault at the Point of Common Coupling (PCC) and a step change in AC system frequency. For these test scenarios, the EPLL suffers noticeable periodic ripples during the dynamic process due to phase and amplitude jumps, with slower response time and steady oscillations during frequency change. But, these drawbacks are significantly mitigated by the MSSI-EPLL, as proven mathematically and confirmed through simulation studies.