LCL filter design and inductor current ripple analysis for a three-level NPC grid interface converter

Abstract

The harmonic filter for a three-level neutral-point-clamped (NPC) grid interface converter is designed in this paper with good filtering performance and small component size. LCL topology is selected because of the attenuation and size tradeoff. The design of the inverter-side inductor L 1 is emphasized due to its cost. A detailed inductor current ripple analysis is given based on the space vector modulation. The analysis derives the inductor volt-second and the maximum current ripple equation in line cycle. It also reveals the switching cycle current ripple distribution over a line cycle, with the consideration of power factor. The total system loss is calculated with different ripple current. Inductor L 1 is determined by the loss and size tradeoff. Also the capacitor- and grid-side inductor L 2 is designed based on attenuation requirement. Different damping circuits for LCL filter are compared and investigated in detail. The filter design is verified by both simulation and 200-kVA three-level NPC converter hardware.