Leakage-Ground Currents Compensation in a Transformerless HB-NPC Topology Using a DC-Link-Tied LC Filter for Photovoltaic Applications

Abstract

In this article, a solution to mitigate the leakage-ground currents (LGCs) in a grid-tied H-bridge neutral-point-clamped inverter is presented. This solution consists in splitting the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter capacitor and connecting each capacitor to a dc-link terminal. The proposal is referred to as the dc-link-tied <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> output filter. Out of this hardware modification, it is not necessary to increase the number of switches nor design a new modulation scheme. Furthermore, a formal analysis is provided based on the common-mode (CM) model describing the role of this particular connection of the output <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter on the minimization of the LGC. In addition, a closed-loop control strategy has been implemented to allow testing the prototype connected to the electrical grid. The mitigation of the LGCs has been evaluated under this condition as well. To validate the proposed circuit modification, numerical simulations and experimental tests have been performed in a 1-kW laboratory prototype of the H-bridge neutral-point-clamped inverter with the dc-link-tied <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter solution.