| MS Seminar

Name of the Speaker: Mr. Bishal Mondal (EE16D406)
Guide: Dr. Arun Karuppaswamy
Venue: ESB-244 (Seminar Hall)
Date/Time: 30th January 2024 (Tuesday), 2:30 PM
Title: Analysis, design and control of grid-connected inverter with output LCL filter

Abstract

Grid-connected inverters (GCIs) have a wide range of useful applications. A few examples of GCIs are active front-end converter (AFEC), static synchronous compensator (STATCOM), shunt active filter (SAF), and GCI for distributed generation applications (DGAs). The research work spans various analysis, design, and control aspects of GCIs. An improved phase-locked loop (PLL), converter-side inductor ripple analysis, a new design approach for the LCL filter, and current controller design are the broad research aspects of this work. In seminar talk I, the proposed improvements in PLL were presented. In this talk, the proposed design method for the LCL filter will be discussed.

LCL filters with passive damping are widely used for GCI applications. This work proposes a novel non-iterative component selection procedure for the LCL filter with passive RC 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.

The proposed approach has several novel contributions. Firstly, the proposed design approach is non-iterative. It is observed that the existing design method usually considers the damping resistor (Rd) after selecting the other LCL filter components. This leads to iterations since Rd alters the attenuation at the switching frequency. In this work, a grid-side inductance factor is used that includes the effect of Rd at an early design stage, thereby avoiding iterations. Secondly, a methodical approach to the selection of Rd is proposed which ensures a high impact of resistance at the resonance frequency and it also offers a minimum quality factor for the filter. Thirdly, the literature indicates that a critically flat resonance peak is important for control stability. The additional degree of freedom to split the total shunt capacitance into two non-identical values is used to achieve a critically flat resonance peak. A capacitor split factor "n" is used for this purpose. An analytical method is proposed to find the range of "n" that ensures a critically flat resonance peak. A value of "n" is chosen from the available range to meet the other desirable constraints -- the damping resistor loss, voltage drop across the total series inductance, and the resonant frequency range. The work also explores the impact of grid inductance variation on the filter performance. This is accomplished through an analysis of the filter's damping characteristics and the stability of its current controller across a range of grid inductances.