Stability Analysis of Three-Phase Stand-Alone Inverters with LCL Filter

The LCL filter is widely used in distributed generation systems. This filter provides a good harmonic attenuation and has smaller physical size when compared with the L filter. One drawback of this filter is its inherent resonance that may lead the system to instability or degrade the performance of the system. The stability of the system is analyzed in the literature just for the grid-tied inverter, but the resonance also damage the power quality when the inverter is in the stand-alone mode of operation. This paper aims to analyze the stability of the inverter operation in stand-alone mode with LCL output filter. The control is done using PI controller in the voltage loop and P controller in the damping loop. The analysis is carried out based in root contour and Bode diagrams. Simulation results ensure the theoretical analysis.