Analysis of Inverter Output Current Ripple and Design of Inverter-Side Output Filter Inductor for Grid-Connected Applications

Abstract

Incisive selection of the $\bm {LCL}$ filter parameters for a grid-connected inverter (GCI) is crucial to meet the grid interconnection standards with a reduced hardware footprint. Various design methods are available in the literature for selecting the $\bm {LCL}$ filter parameters. While the grid-side inductor of the $\bm {LCL}$ filter can utilize an iron core and follow the standard grid frequency inductor design, the inverter-side inductor design needs attention since it has significant switching frequency harmonics. This paper presents an extensive discussion on the design of the inverter-side inductor for GCIs. The inverter-side inductor ($\bm {L}_{\bm {i}}$) is calculated based on the allowable inverter peak-peak ripple current to reduce the losses due to the ripple component. The value or size of $\bm {L}_{\bm {i}}$ depends on the inverter configuration, switching technique, and the application. The initial sections of the paper present a comprehensive analysis, comparing the value and hence the size of $\bm {L}_{\bm {i}}$ for different wiring configurations and applications. Closed-form expressions are developed for $\bm {L}_{\bm {i}}$ and are used in selecting the minimum value of $\bm {L}_{\bm {i}}$. The suitability of an amorphous core for the inverter-side inductor is discussed. The amorphous-core inductor designs in literature can lead to a wide variation of inductance with current and have been analyzed to cause differential and common mode noise. To address this, a novel amorphous-core inductor design is proposed in the later sections of this work. The proposed approach ensures a minimal variation in the inductance over the operating current range. Experimental results are provided to support the various theoretical assertions.