Performance analysis of fractional‐order modified SRF PLL under grid abnormalities

Abstract

This article proposes two different structures of fractional‐order modified synchronous reference frame phase‐locked loop (MSRF PLL) and discusses their performance under different grid abnormalities. Phase‐locked loop (PLL) is a type of closed‐loop feedback control system that ensures phase and frequency coherence between its input and output signals. The basic synchronous reference frame phase‐locked loop (SRF‐PLL) is a conventional synchronization technique that is frequently employed in grid‐connected systems for power electronic converters. The SRF‐PLL offers rapid and precise phase/frequency detection under ideal grid environments. However, its performance is severely hampered under unbalanced and distorted grid environments. This paper discusses two new configurations of fractional‐order (FO) modified SRF (MSRF), one with fractional order only in additional low‐pass filter of first order (FO‐LP) and another fractional order in both first‐order low‐pass filter and PI (FO‐LPFO‐PI) of MSRF. These controllers are assembled using FOs “a” and “b” with limits as 0 < a < 2 and 0 < b < 2. The performance analysis of proposed FO MSRFs is done under grid abnormalities like voltage sag and swell, polluted grid supply, frequency change, phase change, and variables for dc offset. The outcomes of simulation are acquired using FO modeling and control (FOMCON) toolbox for MATLAB/SIMULINK, and the experimental results are validated with simulation results. A fair comparison among the MSRF‐PLL, FO‐LP MSRF‐PLL, and FO‐LPFO‐PI MSRF‐PLL is also depicted during grid abnormalities.