Three-Phase Transformerless PV Inverter With Reconfigurable LCL Filter and Reactive Power Capability

Constructing LCL filter with only three inductors is made possible by a topology called the reconfigurable filter in three-phase converters, in which the filter is reconfigured six times during the ac line cycle. While the existing reconfigurable filter reduces the magnetic components by half, it cannot be installed as an add-on filter to existing converters due to requiring a dc link connection. In this article, a novel reconfigurable LCL filter applied in photovoltaic transformerless inverters is proposed, which not only inherits the merits of the existing reconfigurable filter but also eliminates the need for a dc link connection, enabling easy installation in existing converters. In addition, the proposed reconfigurable filter effectively clamps the common-mode voltage to neutral at high frequencies, resulting in the reduction of leakage current. Therefore, the proposed topology offers several advantages with one solution, including injecting high-quality grid current, magnetic component reduction, leakage current reduction, compatibility with add-on installations, and reactive power support. Comprehensive equivalent circuits, modeling, and analysis are provided to study the operation modes, leakage current capability, and loss breakdown of the proposed topology. The proposed topology is verified and compared with the existing reconfigurable filter by a 1-kW experimental prototype. All the experimental results agree with the theoretical concepts.