A Non-Iterative Design Method for Output LCL Filter with RC Damping in Grid-Connected Inverters

Abstract

<p><em>LCL</em> filters with passive damping are widely used for grid-connected inverter (GCI) applications. This work proposes a novel non-iterative component selection procedure for the <em>LCL</em> filter with passive <em>RC</em> damping. While the primary goal of the filter is to effectively attenuate the switching frequency components of the inverter, there are several other desirable constraints that make the selection procedure challenging. In this work, eight such desirable constraints are identified from the existing literature and the proposed method meets all the identified constraints. Besides being non-iterative, the novelty of the work primarily lies in the selection of the damping resistor <em>R</em>_<em>d</em> and the ratio <em>n</em> in which the total shunt capacitor is split. The primary intent of <em>R</em>_<em>d</em> being to damp the resonance, a methodical approach that ensures a high impact of the resistance at the resonance frequency is proposed. The proposed approach also ascertains a minimum possible quality factor. The selection of the ratio <em>n</em> is leveraged as an additional degree of freedom. An analytical method to find the range for <em>n</em> that offers a critically flat resonance peak is proposed. A critically flat resonance peak is important for control stability. The final value of <em>n</em> is chosen from the available range to meet all the constraints. </p>