This paper presents a design technique of magnetic integrated LLCL filters for grid-tied inverters. With the proposed design technique, the LLCL filter's resonant frequency can be higher than the Nyquist frequency. Furthermore, the proposed concept was only reported for the LCL filter in the previous research works. In addition, the modulation process will produce dominant switching harmonics for unipolar PWM H-bridge inverters at the double switching frequency. Thus, putting the resonant frequency beyond the Nyquist frequency will increase the stability zone. The proposed design methods maximize the filter inductors' utilization and resist the grid impedance variations under weak grid conditions, depending on the improved stability zone. Comparative simulation and HIL experimental results are presented to confirm the effectiveness of the proposed magnetic integrated LLCL filter design. The HIL experimental results and the simulation results agree well with each other.

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Modulating the traction converters produces current harmonics at the switching frequencies and their multiples. These harmonics should be minimized to meet the network specifications. The LC‐trapped filters, tuned to these frequencies, can easily meet this requirement, but the existing applicable trap filters have not been studied with the traditional traction system topologies. Thus, this paper presents a trapped LCL filter with an LC resonator on the converter side, called a fully integrated T‐LCL filter, for the traction power supply system. The model and analysis reported in this research demonstrate that the presented filter has several advantages, which can be summarized by: reducing the size by winding many coils through magnetic integration, attenuating the switching frequency and its multiple harmonics that reduce the current total harmonic distortion, assuring durability against the filter parameters differences, and preserving system stability under transient conditions. The proposed filter can become a promising trap filter based on these advantages. Simulation models of an ac/dc single‐phase traction rectifier with the proposed filter were created and tested in MATLAB/Simulink, verifying its superiority. Finally, the filter is validated by performing hardware‐in‐the‐loop experiments.

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