A second-order generalized integrator phase-locked loop with a cascaded structure incorporating a low-pass filter

Renewable energy sources (RESs) have achieved widespread global adoption owing to their favourable environmental impacts, together with their inherent sustainability, cost-effectiveness, and controllability. A phase-locked Loop (PLL) is one of the most widely used synchronisation techniques owing to its speed and robustness. This study was developed to address the problem that the traditional second-order generalised integrator-based PLL(SOGI-PLL) fails to achieve correct phase locking under non-ideal grid conditions in single-phase grid synchronization, using a cascaded structure that combines the traditional SOGI with a SOGI incorporating a LPF(SOGI-LPF) .Then, the transfer functions of the improved method and the traditional methods were analysed using Bode diagrams and root locus techniques. The improved PLL was tested on the RTDS/RCP hardware-in-the-loop experimental platform. Moreover, to compare its performance with that of the SOGI and SOGI-LPF methods in terms of indicators such as settling time, and phase error, several scenarios were developed. As a result, the improved PLL demonstrates the fastest dynamic response and, completely rejects four operating conditions—single-phase voltage sag, phase jump, low-order harmonics, and DC offset in the grid. Furthermore, compared with the first two PLLs, the transient phase-locking error of the improved PLL is reduced by up to 80 %.