Passivity-Based Stability Design of LCL-Filtered Converters: An Overview

The stability of LCL-type grid-connected converters in distributed power generation systems (DPGS) have been numerously investigated. It is well known that resonance of high-order filters may cause system oscillations and grid current distortion. This phenomenon is more critical when the DPGS contains capacitive loads and cables. Thus, it needs to consider the interaction effect between the equivalent grid impedance and the converter impedance, for which have been addressed by many innovative passivity methods. This paper reviews contributions and classifies of the existing passivity methods with different current controls as single-loop and multi-loop. Based on the concept of passivity, all passivity methods can guarantee the stability of the system by reshaping the output impedance. Several promising methods for different grid impedances are reviewed and evaluated. Finally, suggestions for implementing passivity and future trends are presented.