Design of the LLC Filter for AC Grid-Based Converter

This paper emphasizes reducing harmonic distortion in the electrical current delivered by photovoltaic (PV) inverters to the power grid. It highlights the issue of significant harmonic components present in the output voltage of inverters, which is attributed to pulse width modulation (PWM) switching techniques. This necessitates the deployment of LCL filters as a strategic approach to limit current harmonics effectively. Additionally, it explores the relatively under-investigated area of the double-frequency unipolar PWM switching strategy, which is noted for its potential benefits, including diminished harmonic distortion and enhanced operational efficiency, despite the challenges it presents, such as the risk of common-mode leakage current in systems without transformers. It also discusses the design of LCL filters, setting the stage for the possible adoption of the double-frequency PWM technique in transformer-less single-phase PV inverters connected to the grid. Through theoretical analysis and simulation studies using MATLAB/SIMULINK, a comprehensive and understandable guide for designing LCL filters.