Neutral current harmonic analysis and inhibition for two-stage four-leg matrix converter

There is an increasing interest in two-stage four-leg matrix converter (3×4TSMC) which provides a neutral connection for potential imbalanced loads. However, the fourth leg will worsen its operation performance unexpectedly, even if connected to the balanced loads. By means of analysis and calculation, it is found that the input filter capacitor voltage fluctuation will transfer to the output in the process of modulation, generating input frequency related harmonic in neutral current and distorting output voltage waveforms. To suppress this low-frequency harmonic, an improved time-varying repetitive control (TRC) scheme, which uses linear interpolation other than changing sampling period to obtain satisfactory harmonic rejection in frequency conversion system, is proposed. Its specific hardware implementation is presented on the heels. The correctness of harmonic analysis and validity of the control method are verified by experiments.