An LTCL Filter for Three-Phase Grid-Connected Converters

This paper presents a new high-order filter for three-phase grid-connected voltage source converters (VSCs) named the inductor-trap-capacitor-inductor (LTCL) filter, in which multiple LC trap filters are inserted in parallel with the branch of the capacitor in the traditional LCL filter to compose multiple series resonant circuits at the selected frequencies. Particularly, the LTCL filter can attenuate the harmonic currents around the multiples of switching frequencies and guarantee -60 dB/decade attenuation in the high-frequency band, leading to a decrease of the total inductance and volume. Furthermore, within half of the switching frequency range, an LTCL -filter-based grid-connected VSC has almost the same frequency-response characteristic as that with the traditional LCL filter. That is to say, the LTCL filter does not bring any extra control difficulties. The basic parameter selection criteria and the parameter design procedure of the LTCL filter are introduced. Moreover, the sensitivity analysis of the LTCL filter is analyzed and discussed in detail. The comparative analysis and discussion considering the LCL filter, the LLCL filter, the multituned traps filter, and the proposed LTCL filter, have been presented and evaluated through the experiments on a 65-kW three-phase grid-connected VSC prototype.