An Efficient High-Power-Density Integrated Trap-LCL Filter for Inverters

To improve power density of voltage-source converters, passive filters or combination of passive components known as trap filters are normally used, which are designed to block or bypass switching current harmonics to meet grid requirements. Recently, researchers have investigated the magnetic integration of trap filters into LCL structure, reducing the filter required inductance. This article proposes a novel method of integrating the trap and converter-side inductances without any electrical connections. As a result, the trap inductance does not carry the line frequency current, reducing the conduction loss. This also enables the use of modern core materials with small sizes and low core loss, resulting in further power density improvements. This method offers an additional degree-of-freedom to locate the filter resonant poles in designated frequencies and avoid triggering any harmonics. Based on this approach, it is also possible to use multiple traps coupled on a single core. The circuit models and frequency response of this filter are derived, and the design procedure is demonstrated. A comprehensive comparison with LCL filters and other integration methods is performed using FEM simulations and experimental results for a 500 W/110 V and a 5 kW/240 V inverter. The proposed filter provides the most efficient and smallest size among all the scenarios that comply with IEEE519-2020 standard.