Comprehensive Analysis of Virtual Impedance-Based Active Damping for LCL Resonance in Grid-Connected Inverters

摘要

LCL filters have been widely applied as the interface between voltage source inverters (VSIs) and power grid. However, inherent LCL resonance complicates the design of current control or even threatens system stability. Extensive approaches have been proposed to deal with the resonance, among which the active damping (AD) methods realized by the feedback of filter state variables are proved to be effective and robust. In this paper, a comprehensive analysis of such AD by utilizing its virtual circuit property is presented. It is found that different filter state variables can be selected to achieve the effective damping functions by emulating proper virtual impedances (VIs). Meanwhile, the connection of the VI with the LCL network is not restricted by the selected state variable but mainly dependent on the applied AD controller, which, in result, enables a thorough investigation of such VI-based AD methods. Consequently, all possible forms of the AD controller to realize different connection types by utilizing different state variables are derived. The optimal selection of the AD controller together with the specific state variable is further analyzed, where the obtained results can be used to guide the design of such AD in practice. Finally, the correctness of the theoretical analyses are verified by the experimental results.