Investigation on Grid Synchronization Techniques of Grid tied Solar PV System using Pre Filter based Phase Locked Loop

Abstract

In the current scenario, the integration of solar photovoltaic (PV) system with variable power production into power grids requires a power converter with robust control techniques. In order to formulate the control strategy meticulously, fast and accurate detection of grid phase angle is necessary. Hence, the frequency and phase angle of the grid voltages are vital components to guarantee the synchronization of the grid connected converter. Additionally, a phase locked loop (PLL) based control algorithm is needed to generate the accurate reference current for the grid-connected converter. PLL is mandatory to track the frequency, and phase angle and filter out the harmonics, interharmonics, and DC offset during distorted grid conditions. This thesis proposes a modified sliding Goertzel discrete Fourier transform (SGDFT) based PLL and an adaptive band-pass filter (ABPF) based PLL to extract the fundamental component during distorted grid conditions. The modified SGDFT based PLL is designed using three degrees of freedom (DOF) of second-order fraction delay using the Lagrange interpolation method to alleviate the integer and noninteger frequency components and strong against several distorted grid conditions, namely, voltage sag, high-frequency harmonics, interharmonics, and DC offset. Furthermore, the proposed PLL precisely extracts the fundamental frequency and phase angle with the faster transient response and attains superior system stability. The detailed mathematical modeling of recommended PLL is analyzed with existing PLLs, such as harmonic, interharmonic, and DC offset PLL (HIHDO PLL), hybrid prefiltering stage PLL (HPFS PLL), and SGDFT-based PLL.