A robust modified notch filter based SOGI-PLL approach to control multilevel inverter under distorted grid

Abstract

This paper introduces a novel approach to enhance the control algorithm for a single-phase shunt active power filter(SAPF) by integrating a new technique into a 5-level cascaded multilevel inverter (MLI) with Photo Voltaic (PV) array integration. Due to the integration of non-linear loads in the grid, such as computers, variable speed drives, and other solid-state equipment, non-sinusoidal currents are drawn, introducing harmonics that distort the voltage and current waveforms. It is essential to mitigate these harmonics, and integrating Shunt Active Power Filters (SAPFs) gives the grid the ability to inject active power. In order to improve power quality and achieve active and reactive power balance, this integration requires an imperative control method. This work extracts the fundamental component of the load current and efficiently handles grid distortions such as DC offset, phase shift, and harmonics using a phase lock loop (PLL) based on a Modified Notch Filter Second Order Generalised Integrator (MNFSOGI). Using MATLAB/Simulink software modelling, experimental validation utilising the OPAL-RT real-time data simulator verifies the proposed system's operation. The control algorithm, which has been painstakingly designed and verified, allows feed-forward current estimate from the PV array, synchronization template obtained from the grid voltage signal, and estimation of both fundamental and non-linear load currents. The performance of the MNFSOGI-PLL is additionally compared with that of the conventional E-PLL, MAF-PLL and DSOGI-PLL techniques. By attaining power balance in multilevel inverters under distorted grid conditions, this research substantially contributes to improving power quality. According to simulation and experimental results, the Total Harmonic Distortion (THD) of the grid current is found to be 1.50% in normal grid and 3.96% in distorted grid which is less than 5%, by IEEE-1547 standards. Moreover, the limitations of the presented multilevel inverter system are highlighted by the disadvantages of traditional 2-level inverters, which include increased harmonics, restricted voltage levels, and poorer power quality.

Keywords

• Power quality
• Shunt active power filter
• Multilevel inverter
• Adaptive control