Performance assessment of L-2LC-L filter (double LC trap)-based grid-connected three-phase voltage source inverter

Abstract

Inverter-Based Distributed Generation (IBDG) units are typically coupled to the grid via three-phase Voltage Source Converters (VSCs). The IBDGs may pollute utility with the injected harmonic currents. In order to meet the standards' requirements, the necessity of grid-integration through passive filters supports a reduction of harmonic currents. This paper presents a performance assessment for the harmonic reduction introduced on the grid-side inductor when using LLCL filter with a single LC-trap, and LLCL filter with a dual LC-trap, named here L-2LC-L filter. Moreover, it can be deduced theoretically, that the higher the number of the LC parallel branches, the lower the grid-side inductor. When connected between the VSC and the grid, these types of filters may introduce resonance. Therefore, a passive or active damping technique may be applied to suppress the resonance. This paper presents also through simulation, analysis, and experiment, an active damping approach for LCL filter as well as for a filter with single trap (LLCL) and for a filter with dual LC trap (L-2LC-L) with grid-interfaced three-phase VSC.