Comparative Performance Analysis of LCL, LLCL, L(LCL)₂ and L(LCL)₃ Filter Topologies for High-power Grid-connected Solar PV Inverters

Abstract

Advanced passive filter topologies are increasingly required in modern high-power grid-connected solar PV systems to ensure compliance with stringent harmonic and power quality standards. Conventional LCL-based filters often face limitations in multi-frequency harmonic attenuation, stability under weak grid conditions, and scalability for high-voltage applications. This paper presents a rigorous comparative analysis of four passive filter topologies, LCL, LLCL, L(LCL)₂, and the novel L(LCL)₃, for harmonic mitigation in high-power grid-connected solar PV inverter systems. Evaluation metrics encompass Total Harmonic Distortion (THD), attenuation at the switching frequency and its harmonics, Power Spectral Density (PSD) characteristics, filter losses, efficiency, component count, physical size, material cost, stability margin, and weak grid suitability. Results from MATLAB/Simulink simulation of a 100 MVA, 33 kV reference system demonstrate that the L(LCL)₃ filter achieves the best harmonic performance: grid-side THD of 1.3% (vs. 4.2% for LCL), switching-frequency attenuation of −90 dB (vs. −60 dB for LCL), and PSD reduction of 3,000:1 at the second harmonic. Filter efficiency is comparable across all topologies (99.51–99.53%), with total losses ranging from 445.8 kW (LLCL, minimum) to 468.6 kW (LCL, maximum). The L(LCL)₃ filter exhibits excellent stability characteristics (stability margin: Excellent; Q = 2.55) and the highest suitability for weak grid conditions, making it the preferred choice for Nigeria's power grid environment. Material cost is approximately 65% higher than the LCL baseline, offset by superior performance and lifetime operational benefits.