I. Introduction
The application of renewable energy resources such as wind turbines and photovoltaic units has significantly grown in the past decade. The interface between these renewable energy resources and the utility grid is handled by inverters. In order to satisfy the power quality standards specified by IEEE Standard 1547, the output current of an inverter needs to be filtered using passive filters such as L, LC, and LCL filters which eliminate the switching frequency harmonics [1]–[7]. Compared to an L filter, LC and LCL filters are cheaper, less costly, smaller in size, and more effective in terms of attenuation. But these high-order filters generate undesired resonances, which make the controller design problem more challenging to sufficiently damp them [8]–[10]. Adding additional resistance to the output filter, which is considered as a “passive damping” approach, increases the system loss and hence decreases efficiency [11]. The alternative approach is called “active damping”, which attenuates the undesired resonances by using a control feedback loop [8], [12], [13].